EP3079204B1 - Two-dimensionally electronically-steerable artificial impedance surface antenna - Google Patents
Two-dimensionally electronically-steerable artificial impedance surface antenna Download PDFInfo
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- EP3079204B1 EP3079204B1 EP16157596.4A EP16157596A EP3079204B1 EP 3079204 B1 EP3079204 B1 EP 3079204B1 EP 16157596 A EP16157596 A EP 16157596A EP 3079204 B1 EP3079204 B1 EP 3079204B1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/20—Non-resonant leaky-waveguide or transmission-line antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/28—Non-resonant leaky-waveguide or transmission-line antennas; Equivalent structures causing radiation along the transmission path of a guided wave comprising elements constituting electric discontinuities and spaced in direction of wave propagation, e.g. dielectric elements or conductive elements forming artificial dielectric
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/006—Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces
- H01Q15/0066—Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces said selective devices being reconfigurable, tunable or controllable, e.g. using switches
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
- H01Q21/061—Two dimensional planar arrays
- H01Q21/068—Two dimensional planar arrays using parallel coplanar travelling wave or leaky wave aerial units
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/24—Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
- H01Q3/44—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element
- H01Q3/443—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the electric or magnetic characteristics of reflecting, refracting, or diffracting devices associated with the radiating element varying the phase velocity along a leaky transmission line
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/0006—Particular feeding systems
- H01Q21/0012—Radial guide fed arrays
Definitions
- the present disclosure relates generally to antennas and, in particular, to electronically-steerable antennas. Still more particularly, the present disclosure relates to an electronically-steerable artificial impedance antenna capable of being steered in two dimensions.
- steering an antenna may include directing the primary gain lobe, or main lobe, of the radiation pattern of the antenna in a particular direction.
- Electronically steering an antenna means steering the antenna using electronic, rather than mechanical, means. Steering an antenna with respect to two dimensions may be referred to as two-dimensional steering.
- phased array antennas typically provide two-dimensional steering.
- phased array antennas have electronic configurations that are more complex and/or more costly than desired. Consequently, having some other type of antenna that can be electronically steered in two dimensions and that is low-cost relative to a phased array antenna may be desirable.
- An artificial impedance surface antenna may be less expensive than phased array antennas.
- An artificial impedance surface antenna may be implemented by launching a surface wave across an artificial impedance surface (AIS) having an impedance that is spatially modulated across the artificial impedance surface according to a function that matches the phase fronts between the surface wave on the artificial impedance surface and the desired far-field radiation pattern.
- the basic principle of an artificial impedance surface antenna operation is to use the grid momentum of the modulated artificial impedance surface to match the wave vectors of an excited surface wave front to a desired plane wave.
- Some low-cost artificial impedance surface antennas may only be capable of being electronically steered in one dimension.
- mechanical steering may be used to steer a one-dimensional artificial impedance surface antenna in a second dimension.
- mechanical steering may be undesirable in certain applications.
- a two-dimensional electronically-steerable artificial impedance surface antenna has been described in prior art.
- this type of antenna is more expensive and electronically complex than desired.
- electronically steering this type of antenna in two dimensions may require a complex network of voltage control for a two-dimensional array of impedance elements. This network is used to create an arbitrary impedance pattern that can produce beam steering in any direction.
- a two-dimensional artificial impedance surface antenna may be implemented as a grid of metallic patches on a dielectric substrate. Each metallic path may be referred to as an impedance element.
- the surface wave impedance of the artificial impedance surface may be locally controlled at each position on the artificial impedance surface by applying a variable voltage to voltage-variable varactors connected between each of the patches.
- a varactor is a semiconductor element diode that has a capacitance dependent on the voltage applied to this diode.
- the surface wave impedance of the artificial impedance surface can be tuned with capacitive loads inserted between the patches.
- Each patch is electrically connected to neighboring patches on all four sides with voltage-variable varactor capacitors.
- the voltage is applied to the varactors through electrical vias connected to each patch.
- An electrical via may be an electrical connection that goes through the plane of one or more adjacent layers in an electronic circuit.
- One portion of the patches may be electrically connected to the ground plane with vias that run from the center of each patch down through the dielectric substrate.
- the rest of the patches may be electrically connected to voltage sources that run through the dielectric substrate, and through holes in the ground plane to the voltage sources.
- Computer control allows any desired impedance pattern to be applied to the artificial impedance surface within the limits of the varactor tunability and the limitations of the surface wave properties of the artificial impedance surface.
- One of the limitations of this method is that the vias can severely reduce the operational bandwidth of the artificial impedance surface because the vias also impart an inductance to the artificial impedance surface that shifts the surface wave bandgap to a lower frequency.
- the varactors are tuned to higher capacitance, the artificial impedance surface inductance is increased, which may further reduce the surface wave bandgap frequency.
- the net result of the surface wave bandgap is that it does not allow the artificial impedance surface to be used above the bandgap frequency. Further, the surface wave bandgap also limits the range of surface wave impedance to that which the artificial impedance surface can be tuned.
- an artificial impedance surface antenna that can be electronically steered in two dimensions and that is less expensive and less complex than some currently available two-dimensional artificial impedance surface antennas, such as the one described above, may be desirable in certain applications. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.
- Surface scattering antennas provide adjustable radiation fields by adjustably coupling scattering elements along a wave-propagating structure.
- the scattering elements are patch elements.
- the scattering elements are made adjustable by disposing an electrically adjustable material, such as a liquid crystal, in proximity to the scattering elements. Methods and systems provide control and adjustment of surface scattering antennas for various applications.
- EP2822096 according to its abstract: An apparatus (100) comprising a plurality of radiating elements (122,123) and a plurality of surface wave feeds (130). Each radiating element in the plurality of radiating elements comprises a number of surface wave channels (125) in which each of the number of surface wave channels is configured to constrain a path of a surface wave. A surface wave feed in the plurality of surface wave feeds is configured to couple a surface wave channel in the number of surface wave channels of a radiating element in the plurality of radiating elements to a transmission line (156) configured to carry a radio frequency signal.
- an apparatus according to clam 1 is provided.
- an antenna system comprises a plurality of radiating elements and a plurality of surface wave feeds.
- Each of the plurality of radiating elements comprises a number of surface wave channels in which each of the number of surface wave channels is configured to constrain a path of a surface wave.
- Each of the number of surface wave channels comprises a plurality of impedance elements located on a surface of a dielectric substrate and a plurality of switch elements located on the surface of the dielectric substrate.
- Each of the plurality of switch elements has only two states.
- the plurality of surface wave feeds is configured to couple the number of surface wave channels of each of the plurality of radiating elements to a number of transmission lines.
- Antenna system 100 may include antenna 102, voltage controller 104, phase shifter 106, and radio frequency module 108.
- Antenna 102 takes the form of artificial impedance surface antenna (AISA) 110 in this illustrative example.
- AISA artificial impedance surface antenna
- Antenna 102 is configured to transmit and/or receive radiation pattern 112.
- Radiation pattern 112 is a plot of the gain of antenna 102 as a function of direction.
- the gain of antenna 102 may be considered a performance parameter for antenna 102. In some cases, "gain" is considered the peak value of gain.
- Antenna 102 is configured to electronically control radiation pattern 112.
- radiation pattern 112 may be the strength of the radio waves transmitted from antenna 102 as a function of direction.
- Radiation pattern 112 may be referred to as a transmitting pattern when antenna 102 is used for transmitting.
- the gain of antenna 102, when transmitting, may describe how well antenna 102 converts electrical power into electromagnetic radiation, such as radio waves, and transmits the electromagnetic radiation in a specified direction.
- radiation pattern 112 may be the sensitivity of antenna 102 to radio waves as a function of direction. Radiation pattern 112 may be referred to as a receiving pattern when antenna 102 is used for receiving.
- the gain of antenna 102 when used for receiving, may describe how well antenna 102 converts electromagnetic radiation, such as radio waves, arriving from a specified direction into electrical power.
- the transmitting pattern and receiving pattern of antenna 102 may be identical. Consequently, the transmitting pattern and receiving pattern of antenna 102 may be simply referred to as radiation pattern 112.
- Radiation pattern 112 may include main lobe 116 and one or more side lobes.
- Main lobe 116 may be the lobe at the direction in which antenna 102 is being directed.
- main lobe 116 is located at the direction in which antenna 102 transmits the strongest radio waves to form a radio frequency beam.
- main lobe 116 may also be referred to as the primary gain lobe of radiation pattern 112.
- antenna 102 is used for receiving, main lobe 116 is located at the direction in which antenna 102 is most sensitive to incoming radio waves.
- antenna 102 is configured to electronically steer main lobe 116 of radiation pattern 112 in desired direction 114.
- Main lobe 116 of radiation pattern 112 may be electronically steered by controlling phi steering angle 118 and theta steering angle 120 at which main lobe 116 is directed.
- Phi steering angle 118 and theta steering angle 120 are spherical coordinates.
- phi steering angle 118 is the angle of main lobe 116 in the X-Y plane relative to the X-axis.
- theta steering angle 120 is the angle of main lobe 116 relative to a Z-axis that is orthogonal to the X-Y plane.
- Antenna 102 may operate in the X-Y plane by having array of radiating elements 122 that lie in the X-Y plane.
- an "array" of items may include one or more items arranged in rows and/or columns.
- array of radiating elements 122 may be a single radiating element or a plurality of radiating elements.
- each radiating element in array of radiating elements 122 may take the form of an artificial impedance surface, surface wave waveguide structure.
- Radiating element 123 may be an example of one radiating element in array of radiating elements 122. Radiating element 123 may be configured to emit radiation that contributes to radiation pattern 112.
- radiating element 123 is implemented using dielectric substrate 124.
- Dielectric substrate 124 may be implemented as a layer of dielectric material.
- a dielectric material is an electrical insulator that can be polarized by an applied electric field.
- Radiating element 123 may include one or more surface wave channels that are formed on dielectric substrate 124.
- radiating element 123 may include surface wave channel 125.
- Surface wave channel 125 is configured to constrain the path of surface waves propagated along dielectric substrate 124, and surface wave channel 125 in particular.
- array of radiating elements 122 may be positioned substantially parallel to the X-axis and arranged and spaced along the Y-axis. Further, when more than one surface wave channel is formed on a dielectric substrate, these surface wave channels may be formed substantially parallel to the X-axis and arranged and spaced along the Y-axis.
- impedance elements and tunable elements located on a dielectric substrate may be used to form each surface wave channel of a radiating element in array of radiating elements 122.
- surface wave channel 125 may be comprised of plurality of impedance elements 126 and plurality of tunable elements 128 located on the surface of dielectric substrate 124. Together, plurality of impedance elements 126, plurality of tunable elements 128, and dielectric substrate 124 form an artificial impedance surface from which radiation is generated.
- An impedance element in plurality of impedance elements 126 may be implemented in a number of different ways.
- an impedance element may be implemented as a resonating element.
- an impedance element may be implemented as an element comprised of a conductive material.
- the conductive material may be, for example, without limitation, a metallic material.
- an impedance element may be implemented as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate, or some other type of conductive element.
- an impedance element may be implemented as a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element.
- a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element.
- a metamaterial may be an artificial material engineered to have properties that may not be found in nature.
- a metamaterial may be an assembly of multiple individual elements formed from conventional microscopic materials. These conventional materials may include, for example, without limitation, metal, a metal alloy, a plastic material, and other types of materials. However, these conventional materials may be arranged in repeating patterns.
- the properties of a metamaterial may be based, not on the composition of the metamaterial, but on the exactingly-designed structure of the metamaterial. In particular, the precise shape, geometry, size, orientation, arrangement, or combination thereof may be exactly designed to produce a metamaterial with specific properties that may not be found or readily found in nature.
- Each one of plurality of tunable elements 128 may be an element that can be controlled, or tuned, to change an angle of the one or more surface waves being propagated along radiating element 123.
- each of plurality of tunable elements 128 may be an element having a capacitance that can be varied based on the voltage applied to the tunable element.
- plurality of impedance elements 126 takes the form of plurality of metallic strips 132 and plurality of tunable elements 128 takes the form of plurality of varactors 134.
- Each of plurality of varactors 134 may be a semiconductor element diode that has a capacitance dependent on the voltage applied to the semiconductor element diode.
- plurality of metallic strips 132 may be arranged in a row that extends along the X-axis.
- plurality of metallic strips 132 may be periodically distributed on dielectric substrate 124 along the X-axis.
- Plurality of varactors 134 may be electrically connected to plurality of metallic strips 132 on the surface of dielectric substrate 124.
- at least one varactor in plurality of varactors 134 may be positioned between each adjacent pair of metallic strips in plurality of metallic strips 132.
- plurality of varactors 134 may be aligned such that all of the varactor connections on each metallic strip have the same polarity.
- Dielectric substrate 124, plurality of impedance elements 126, and plurality of tunable elements 128 may be configured with respect to selected design configuration 136 for surface wave channel 125, and radiating element 123 in particular.
- each radiating element in array of radiating elements 122 may have a same or different selected design configuration.
- selected design configuration 136 may include a number of design parameters such as, but not limited to, impedance element width 138, impedance element spacing 140, tunable element spacing 142, and substrate thickness 144.
- Impedance element width 138 may be the width of an impedance element in plurality of impedance elements 126. Impedance element width 138 may be selected to be the same or different for each of plurality of impedance elements 126, depending on the implementation.
- Impedance element spacing 140 may be the spacing of plurality of impedance elements 126 with respect to the X-axis.
- Tunable element spacing 142 may be the spacing of plurality of tunable elements 128 with respect to the X-axis.
- substrate thickness 144 may be the thickness of dielectric substrate 124 on which a particular waveguide is implemented.
- the values for the different parameters in selected design configuration 136 may be selected based on, for example, without limitation, the radiation frequency at which antenna 102 is configured to operate. Other considerations include, for example, the desired impedance modulations for antenna 102.
- Voltages may be applied to plurality of tunable elements 128 by applying voltages to plurality of impedance elements 126 because plurality of impedance elements 126 may be electrically connected to plurality of tunable elements 128.
- the voltages applied to plurality of impedance elements 126, and thereby plurality of tunable elements 128, may change the capacitance of plurality of tunable elements 128.
- Changing the capacitance of plurality of tunable elements 128 may, in turn, change the surface impedance of antenna 102.
- Changing the surface impedance of antenna 102 changes radiation pattern 112 produced.
- the capacitances of plurality of tunable elements 128 may be varied. Varying the capacitances of plurality of tunable elements 128 may vary, or modulate, the capacitive coupling and impedance between plurality of impedance elements 126. Varying, or modulating, the capacitive coupling and impedance between plurality of impedance elements 126 may change theta steering angle 120.
- Voltage controller 104 may include number of voltage sources 146, number of grounds 148, number of voltage lines 150, and/or some other type of component. In some cases, voltage controller 104 may be referred to as a voltage control network. As used herein, a "number of" items may include one or more items. For example, number of voltage sources 146 may include one or more voltage sources; number of grounds 148 may include one or more grounds; and number of voltage lines 150 may include one or more voltage lines.
- a voltage source in number of voltage sources 146 may take the form of, for example, without limitation, a digital to analog converter (DAC), a variable voltage source, or some other type of voltage source.
- Number of grounds 148 may be used to ground at least a portion of plurality of impedance elements 126.
- Number of voltage lines 150 may be used to transmit voltage from number of voltage sources 146 and/or number of grounds 148 to plurality of impedance elements 126. In some cases, each of number of voltage lines 150 may be referred to as a via. In one illustrative example, number of voltage lines 150 may take the form of a number of metallic vias.
- each of plurality of impedance elements 126 may receive voltage from one of number of voltage sources 146.
- a portion of plurality of impedance elements 126 may receive voltage from number of voltage sources 146 through a corresponding portion of number of voltage lines 150, while another portion of plurality of impedance elements 126 may be electrically connected to number of grounds 148 through a corresponding portion of number of voltage lines 150.
- controller 151 may be used to control number of voltage sources 146. Controller 151 may be considered part of or separate from antenna system 100, depending on the implementation. Controller 151 may be implemented using a microprocessor, an integrated circuit, a computer, a central processing unit, a plurality of computers in communication with each other, or some other type of computer or processor.
- Surface waves 152 propagated along array of radiating elements 122 may be coupled to number of transmission lines 156 by plurality of surface wave feeds 130 located on dielectric substrate 124.
- a surface wave feed in plurality of surface wave feeds 130 may be any device that is capable of converting a surface wave into a radio frequency signal and/or a radio frequency signal into a surface wave.
- a surface wave feed in plurality of surface wave feeds 130 is located at the end of each waveguide in array of radiating elements 122 on dielectric substrate 124.
- the one or more surface waves propagating along radiating element 123 may be received at a corresponding surface wave feed in plurality of surface wave feeds 130 and converted into a corresponding radio frequency signal 154.
- Radio frequency signal 154 may be sent to radio frequency module 108 over one or more of number of transmission lines 156. Radio frequency module 108 may then function as a receiver and process radio frequency signal 154 accordingly.
- radio frequency module 108 may function as a transmitter, a receiver, or a combination of the two.
- radio frequency module 108 may be referred to as transmit/receive module 158.
- radio frequency module 108 when configured for transmitting, may be referred to as a radio frequency source.
- radio frequency signal 154 may pass through phase shifter 106 prior to being sent to radio frequency module 108.
- Phase shifter 106 may include any number of phase shifters, power dividers, transmission lines, and/or other components configured to shift the phase of radio frequency signal 154. In some cases, phase shifter 106 may be referred to as a phase-shifting network.
- radio frequency signal 154 may be sent from radio frequency module 108 to antenna 102 over number of transmission lines 156.
- radio frequency signal 154 may be received at one of plurality of surface wave feeds 130 and converted into one or more surface waves that are then propagated along a corresponding waveguide in array of radiating elements 122.
- the relative phase difference between plurality of surface wave feeds 130 may be changed to change phi steering angle 118 of radiation pattern 112 that is transmitted or received.
- the relative phase difference between plurality of surface wave feeds 130 may be controlled.
- antenna 102 may be electronically steered in two dimensions.
- radiating element 123 may be configured to emit linearly polarized radiation or circularly polarized radiation.
- the plurality of metallic strips used for each surface wave channel on radiating element 123 may be angled in the same direction relative to the X-axis along which the plurality of metallic strips are distributed. Typically, only a single surface wave channel is needed for each radiating element 123.
- surface wave channel 125 may be a first surface wave channel and second surface wave channel 145 may be also present in radiating element 123.
- Surface wave channel 125 and second surface wave channel 145 may be about 90 degrees out of phase from each other. The interaction between the radiation from these two coupled surface wave channels makes it possible to create circularly polarized radiation.
- Plurality of impedance elements 126 that form surface wave channel 125 may be a first plurality of impedance elements that radiate with a polarization at an angle to the polarization of the surface wave electric field.
- a second plurality of impedance elements that form second surface wave channel 145 may radiate with a polarization at an angle offset about 90 degrees as compared to surface wave channel 125.
- each impedance element in the first plurality of impedance elements of surface wave channel 125 may have a tensor impedance with a principal angle that is angled at a first angle relative to an X-axis of radiating element 123.
- each impedance element in the second plurality of impedance elements of second surface wave channel 145 may have a tensor impedance that is angled at a second angle relative to the X-axis of the corresponding radiating element. The difference between the first angle and the second angle may be about 90 degrees.
- the capacitance between the first plurality of impedance elements may be controlled using plurality of tunable elements 128, which may be a first plurality of tunable elements.
- the capacitance between the second plurality of impedance elements may be controlled using a second plurality of tunable elements.
- plurality of metallic strips 132 on surface wave channel 125 may be angled at about positive 45 degrees with respect to the X-axis along which plurality of metallic strips 132 is distributed.
- the plurality of metallic strips used for second surface wave channel 145 may be angled at about negative 45 degrees with respect to the X-axis along which the plurality of metallic strips is distributed. This variation in tilt angle produces radiation of different linear polarizations, that when combined with a 90 degree phase shift, may produce circularly polarized radiation.
- antenna system 100 in Figure 1 is not meant to imply physical or architectural limitations to the manner in which an example may be implemented.
- Other components in addition to or in place of the ones illustrated may be used. Some components may be optional.
- the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative example.
- phase shifter 106 may not be included in antenna system 100.
- number of transmission lines 156 may be used to couple plurality of surface wave feeds 130 to a number of power dividers and/or other types of components, and these different components to radio frequency module 108.
- number of transmission lines 156 may directly couple plurality of surface wave feeds 130 to radio frequency module 108.
- a tunable element in plurality of tunable elements 128 may be implemented as a pocket of variable material embedded in dielectric substrate 124.
- a "variable material” may be any material having a permittivity that may be varied. The permittivity of the variable material may be varied to change, for example, the capacitance between two impedance elements between which the variable material is located.
- the variable material may be a voltage-variable material or any electrically variable material, such as, for example, without limitation, a liquid crystal material or barium strontium titanate (BST).
- a tunable element in plurality of tunable elements 128 may be part of a corresponding impedance element in plurality of impedance elements 126.
- a resonant structure having a tunable element may be used.
- the resonant structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled resonator, or some other type of resonant structure.
- FIG. 2 an illustration of an antenna system is depicted in accordance with an example.
- Antenna system 200 may be an example of one implementation for antenna system 100 in Figure 1 .
- antenna system 200 includes tunable artificial impedance surface antenna (AISA) 201, which may be an example of one implementation for artificial impedance surface antenna 110 in Figure 1 .
- antenna system 200 may also include voltage controller 202 and phase shifter 203.
- Voltage controller 202 and phase shifter 203 may be examples of implementations for voltage controller 104 and phase shifter 106, respectively, in Figure 1 .
- tunable artificial impedance surface antenna 201 is a relatively low cost antenna capable of being electronically steered in both theta, ⁇ , and phi, ⁇ , directions.
- theta direction may be a direction perpendicular to the Z axis that is perpendicular to the X-Y plane, while the phi direction may be a direction parallel to the X-Y plane.
- tunable artificial impedance surface antenna 201 includes dielectric substrate 206, metallic strips 207, varactors 209, and radio frequency (RF) surface wave feeds 208.
- Metallic strips 207 may be a periodic array of metallic strips 207 that are located on one surface of dielectric substrate 206.
- Varactors 209 may be located between metallic strips 207.
- Dielectric substrate 206 may or may not have a ground plane (not shown in this view) on a surface of dielectric substrate 206 opposite to the surface on which metallic strips 207 are located.
- Steering of the main lobe of tunable artificial impedance surface antenna 201 in the theta direction is controlled by varying, or modulating, the surface wave impedance of tunable artificial impedance surface antenna 201.
- the impedance of tunable artificial impedance surface antenna 201 may be varied, or modulated, by controlling the voltages applied to metallic strips 207 located on the surface of dielectric substrate 206.
- varactors 209 present between metallic strips 207, the voltage applied to varactors 209 may be controlled using metallic strips 207.
- Each of varactors 209 is a type of diode that has a capacitance that varies as a function of the voltage applied across the terminals of the diode.
- the voltages applied to metallic strips 207 may change the capacitance of varactors 209 between metallic strips 207, which may, in turn, change the impedance of tunable artificial impedance surface antenna 201.
- the capacitances of varactors 209 may be varied. Varying the capacitances of varactors 209 may vary or modulate the capacitive coupling and impedance between metallic strips 207 to steer the beam produced by antenna system 200 in the theta direction.
- radio frequency surface wave feeds 208 may be a two-dimensional array of radio frequency surface wave feeds. Steering of the main lobe of tunable artificial impedance surface antenna 201 in the phi direction is controlled by changing the relative phase difference between radio frequency surface wave feeds 208.
- Voltage controller 202 is used to apply direct current (DC) voltages to metallic strips 207 on the structure of tunable artificial impedance surface antenna 201. Voltage controller 202 may be controlled based on commands received through control bus 205. In this manner, control bus 205 provides control for voltage controller 202. Further, control bus 204 may provide control for phase shifter 203. Each of control bus 204 and control bus 205 may be a bus from a microprocessor, a central processing unit (CPU), one or more computers, or some other type of computer or processor.
- CPU central processing unit
- the polarities of varactors 209 may be aligned such that all varactor connections to any one of metallic strips 207 may be connected with the same polarity.
- One terminal on a varactor may be referred to as an anode, and the other terminal may be referred to as a cathode.
- some of metallic strips 207 are only connected to anodes of varactors 209, while other of metallic strips 207 are only connected to cathodes of varactors 209.
- adjacent metallic strips 207 may alternate with respect to which ones are connected to the anodes of varactors 209 and which ones are connected to the cathodes of varactors 209.
- the spacing of metallic strips 207 in one dimension of tunable artificial impedance surface antenna 201 may be a fraction of the radio frequency surface wave wavelength of the radio frequency waves that propagate across tunable artificial impedance surface antenna 201 from radio frequency surface wave feeds 208.
- the spacing of metallic strips 207 may be at most 2/5 of the radio frequency surface wave wavelength of the radio frequency waves.
- the fraction may be only about 2/10 of the radio frequency surface wave wavelength of the radio frequency waves.
- the spacing between varactors 209 connected to metallic strips 207 in a second dimension of tunable artificial impedance surface antenna 201 which may be in a Y direction, may be about the same as the spacing between metallic strips 207.
- Radio frequency surface wave feeds 208 may form a phased array corporate feed structure, or may take the form of conformal surface wave feeds, which are integrated into tunable artificial impedance surface antenna 201.
- the surface wave feeds may be integrated into tunable artificial impedance surface antenna 201, for example, using microstrips.
- the spacing between radio frequency surface wave feeds 208 in the Y direction may be based on selected rules that indicate that the spacing be no farther apart than the free-space wavelength for the highest frequency signal to be transmitted or received.
- the thickness of dielectric substrate 206 may be determined by the permittivity of dielectric substrate 206 and the frequency of radiation to be transmitted or received. The higher the permittivity, the thinner dielectric substrate 206 may be.
- the capacitance values of varactors 209 may be determined by the range needed for the desired impedance modulations for tunable artificial impedance surface antenna 201 in order to obtain the various angles of radiation. Further, the particular substrate used for dielectric substrate 206 may be selected based on the operating frequency, or radio frequency, of tunable artificial impedance surface antenna 201.
- dielectric substrate 206 when tunable artificial impedance surface antenna 201 is operating at about 20 gigahertz, dielectric substrate 206 may be implemented using, without limitation, a substrate, available from Rogers Corporation, having a thickness of about 50 millimeters (mm). In this example, dielectric substrate 206 may have a relative permittivity equal to about 12.2. Metallic strips 207 may be spaced about two millimeters to about three millimeters apart on dielectric substrate 206. Further, radio frequency surface wave feeds 208 may be spaced about 2.5 centimeters apart and varactors 209 may be spaced about two millimeters to about three millimeters apart in this example. Varactors 209 may vary in capacitance from about 0.2 picofarads (pF) to about 2.0 picofarads. Of course, other specifications may be used for tunable artificial impedance surface antenna 201 for different radiation frequencies.
- pF picofarads
- phase shifter 203 may be a one-dimensional phase shifter in this illustrative example. Phase shifter 203 may be implemented using any type of currently available phase shifter, including those used in phased array antennas.
- phase shifter 203 includes radio frequency transmission lines 211 connected to transmit/receive module 210, power dividers 212, and phase shifters 213. Phase shifters 213 are controlled by voltage control lines 216 connected to digital to analog converter (DAC) 214. Digital to analog converter 214 receives digital control signals from control bus 204 to control the steering in the phi direction.
- DAC digital to analog converter
- the main lobe of tunable artificial impedance surface antenna 201 may be steered in the phi direction by using phase shifter 203 to impose a phase shift between each of radio frequency surface wave feeds 208. If radio frequency surface wave feeds 208 are spaced uniformly, then the phase shift between adjacent radio frequency surface wave feeds 208 may be substantially constant.
- the variation of the surface wave impedance, Z sw may be modulated sinusoidally.
- the beam is steered in the theta direction by tuning the voltages applied to varactors 209 such that X , M, and p result in the desired theta steering angle, ⁇ .
- the dependence of the surface wave impedance on the varactor capacitance is calculated using transcendental equations resulting from the transverse resonance method or by using full-wave numerical simulations.
- Voltages may be applied to varactors 209 by grounding alternate metallic strips 207 to ground 220 via voltage control lines 218 and applying tunable voltages via voltage control lines 219 to the rest of metallic strips 207.
- the voltage applied to each of voltage control lines 219 may be a function of the desired theta steering angle and may be different for each of voltage control lines 219.
- the voltages may be applied from digital-to-analog converter (DAC) 217 that receives digital controls from control bus 205 from a controller for steering in the theta direction.
- the controller may be a microprocessor, central processing unit (CPU) or any computer, processor or controller.
- grounding half of metallic strips 207 is that only half as many voltage control lines 219 are required as there are metallic strips 207. However, in some cases, the spatial resolution of the voltage control and hence, the impedance modulation, may be limited to twice the spacing between metallic strips 207.
- FIG. 3 an illustration of a side view of a portion of tunable artificial impedance surface antenna 201 from Figure 2 is depicted in accordance with an example.
- dielectric substrate 206 has ground plane 300.
- Antenna system 400 may be an example of one implementation for antenna system 100 in Figure 1 .
- Antenna system 400 includes tunable artificial impedance surface antenna (AISA) 401, which may be an example of one implementation for artificial impedance surface antenna 110 in Figure 1 .
- AISA artificial impedance surface antenna
- Antenna system 400 and tunable artificial impedance surface antenna 401 may be implemented in a manner similar to antenna system 200 and tunable artificial impedance surface antenna 201, respectively, from Figure 2 .
- antenna system 400 includes tunable artificial impedance surface antenna 401, voltage controller 402, and phase shifter 403.
- Tunable artificial impedance surface antenna 401 includes dielectric substrate 406, metallic strips 407, varactors 409, and radio frequency surface wave feeds 408. Further, antenna system 400 may include transmit/receive module 410.
- voltage controller 402 may be implemented in a manner different from the manner in which voltage controller 202 is implemented in Figure 2 .
- voltage controller 402 may include voltage lines 411 that allow voltage to be applied from digital to analog converter 412 to each of metallic strips 407. Alternating metallic strips 407 are not grounded as in Figure 2 .
- Digital to analog converter 412 may receive digital controls from control bus 205 in Figure 2 from, for example, controller 414, for steering in the theta direction.
- Controller 414 may be implemented using a microprocessor, a central processing unit, or some other type of computer or processor. Steering in the phi direction may be performed using phase shifter 403 in a manner similar to the manner in which phase shifter 203 is used in Figure 2 .
- voltage lines 411 applying voltage to all of metallic strips 407, twice as many control voltages are required compared to antenna system 200 in Figure 2 .
- the spatial resolution of the impedance modulation of tunable artificial impedance surface antenna 401 is doubled.
- the voltage applied to each of voltage lines 411 is a function of the desired theta steering angle, and may be different for each of voltage lines 411.
- Antenna system 500 may be an example of one implementation for antenna system 100 in Figure 1 .
- Antenna system 500 includes tunable artificial impedance surface antenna (AISA) 501, which may be an example of one implementation for artificial impedance surface antenna 110 in Figure 1 .
- AISA artificial impedance surface antenna
- Antenna system 500 and tunable artificial impedance surface antenna 501 may be implemented in a manner similar to antenna system 200 and tunable artificial impedance surface antenna 201, respectively, from Figure 2 . Further, antenna system 500 and tunable artificial impedance surface antenna 501 may be implemented in a manner similar to antenna system 400 and tunable artificial impedance surface antenna 401, respectively, from Figure 4 .
- antenna system 500 includes tunable artificial impedance surface antenna 501, voltage controller 502, and phase shifter 503.
- Tunable artificial impedance surface antenna 501 includes dielectric substrate 506, metallic strips 507, varactors 509, and radio frequency surface wave feeds 508. Further, antenna system 500 may include transmit/receive module 510.
- voltage controller 502 may be implemented in a manner different from the manner in which voltage controller 202 is implemented in Figure 2 and in a manner different from the manner in which voltage controller 402 is implemented in Figure 4 .
- the digital to analog converters of Figure 2 and Figure 4 have been replaced by variable voltage source 512.
- the radiation angle of the beam produced by tunable artificial impedance surface antenna 501 varies between a minimum theta steering angle and a maximum theta steering angle. This range for the theta steering angle may be determined by the details of the design configuration of tunable artificial impedance surface antenna 501.
- the voltage is applied to metallic strips 507 through voltage control lines 514 and voltage control lines 516.
- Voltage control lines 516 may provide a ground for metallic strips 507, while voltage control lines 514 may provide metallic strips 507 with a variable voltage.
- metallic strips 507 are alternately connected to voltage control lines 514 or voltage control lines 516. In other words, alternating metallic strips 507 are grounded.
- Metallic strips 507 may have centers that are equally spaced in the X dimension, with the widths of metallic strips 507 periodically varying with a period ( p ) 518.
- the number of metallic strips 507 in period 518 may be any number.
- metallic strips 507 may be between 10 and 20 metallic strips per period 518.
- the width variation per period 518 may be configured to produce surface wave impedance with a periodic modulation in the X-direction with period 518, such as, for example, the sinusoidal variation of equation (3) described above.
- the surface wave impedance at each point on tunable artificial impedance surface antenna 501 is determined by the width of each of metallic strips 507 and the voltage applied to varactors 509.
- the capacitance of varactors 509 may vary with the varying applied voltage. When the voltage is about 0 volts, the capacitance of a varactor may be at a maximum value of C max . The capacitance decreases as the voltage is increased until the capacitance reaches a minimum value of C min .
- the impedance modulation parameters, X and M as described in equation 2 above, may also vary from minimum values of X min and M min , respectively, to maximum values of X max and M max , respectively.
- dielectric substrate 601 may be used to implement dielectric substrate 206 from Figure 2 , dielectric substrate 406 from Figure 4 , and/or dielectric substrate 506 from Figure 5 .
- Dielectric substrate 601 may have an electrical permittivity that is varied with the application of an electric field.
- Metallic strips 602 are shown located on one surface of dielectric substrate 601. As depicted, no varactors are used in this illustrative example. When a voltage is applied to metallic strips 602, an electric field is produced between adjacent metallic strips 602 and also between metallic strips 602 and ground plane 603. The electric field changes the permittivity of dielectric substrate 601, which results in a change in the capacitance between adjacent metallic strips 602. The capacitance between adjacent metallic strips 602 determines the surface wave impedance of the tunable artificial impedance surface antenna that uses dielectric substrate 601.
- FIG. 7 an illustration of dielectric substrate 601 from Figure 6 having embedded pockets of material is depicted in accordance with an illustrative example.
- dielectric substrate 601 may take the form of inert substrate 700.
- a voltage differential may be applied to adjacent metallic strips 602, which may create an electric field between metallic strips 602 and produce a permittivity change in pockets of variable material 702 located between metallic strips 602.
- Pockets of variable material 702 may be an example of one manner in which plurality of tunable elements 128 in Figure 1 may be implemented.
- the variable material in pockets of variable material 702 may be any electrically variable material, such as, for example, without limitation, a liquid crystal material or barium strontium titanate (BST).
- variable material 702 is embedded in pockets within dielectric substrate 601 between metallic strips 602.
- antenna system 800 may be an example of one implementation for antenna system 100 in Figure 1 .
- Antenna system 800 includes antenna 802, voltage controller 803, phase shifter 804, and radio frequency module 806.
- Antenna 802, voltage controller 803, phase shifter 804, and radio frequency module 806 may be examples of implementations for antenna 102, voltage controller 104, phase shifter 106, and radio frequency module 108, respectively, in Figure 1 .
- Antenna 802 is supplied voltage by voltage controller 803.
- Voltage controller 803 includes digital to analog converter (DAC) 808 and voltage lines 811.
- Digital to analog converter 808 may be an example of one implementation for a voltage source in number of voltage sources 146 in Figure 1 .
- Voltage lines 811 may be an example of one implementation for number of voltage lines 150 in Figure 1 .
- Controller 810 may be used to control the voltage signals sent from digital to analog converter 808 to antenna 802.
- Controller 810 may be an example of one implementation for controller 151 in Figure 1 . In this illustrative example, controller 810 may be considered part of antenna system 800.
- antenna 802 may include radiating structure 812 formed by array of radiating elements 813.
- Array of radiating elements 813 may be an example of one implementation for array of radiating elements 122 in Figure 1 .
- each radiating element in array of radiating elements 813 may be implemented as an artificial impedance surface, surface wave waveguide.
- Array of radiating elements 813 may include radiating elements 814, 815, 816, 818, 820, 822, 824, and 826. Each of these radiating elements may be implemented using a dielectric substrate. Further, each of these dielectric substrates may have a plurality of metallic strips, a plurality of varactors, and a surface wave feed located on the surface of the dielectric substrate that forms a surface wave channel for the corresponding radiating element.
- radiating element 814 may be formed by dielectric substrate 827.
- Plurality of metallic strips 828 and plurality of varactors 830 may be located on the surface of dielectric substrate 827 to form surface wave channel 831.
- surface wave feed 832 may be located on the surface of dielectric substrate 827.
- Plurality of metallic strips 828 and plurality of varactors 830 may be examples of implementations for plurality of metallic strips 132 and plurality of varactors 134, respectively, in Figure 1 .
- surface wave feed 832 feeds a surface wave into surface wave channel 831 of radiating element 814.
- Surface wave channel 831 confines the surface wave to propagate linearly along a confined path across plurality of metallic strips 828.
- surface wave channel 831 creates a region of high surface wave index surrounded by a region of lower surface wave index to confine the surface wave to the set path.
- the surface wave index is the ratio between the speed of light and the propagation speed of the surface wave.
- the regions of high surface wave index are created by plurality of metallic strips 828 and plurality of varactors 830, while the regions of low surface wave index are created by the bare surface of dielectric substrate 827.
- the widths of the regions of high surface wave index may be 50 percent to about 100 percent times the length of the surface wave wavelength.
- Each of plurality of metallic strips 828 located on dielectric substrate 827 may have the same width. Further, these metallic strips may be equally spaced along dielectric substrate 827. Additionally, plurality of varactors 830 may also be equally spaced along dielectric substrate 827. In other words, plurality of metallic strips 828 and plurality of varactors 830 may be periodically distributed on dielectric substrate 827. Further, plurality of varactors 830 may be aligned such that all of the varactors connections of plurality of metallic strips 828 have the same polarity.
- the thickness of dielectric substrate 827 may be determined by its permittivity and the frequency of radiation to be transmitted or received. The higher the permittivity, the thinner dielectric substrate 827 may be.
- the capacitance values of plurality of varactors 830 may be determined by the range needed for the desired impedance modulations for the various angles of radiation.
- the main lobe of the radiation pattern produced by antenna 802 may be electronically steered in the theta direction by applying voltages to the various varactors in array of radiating elements 813. Voltage may be applied to these varactors such that antenna 802 has a surface wave impedance that varies sinusoidally with a distance, x, away from the surface wave feeds on the different dielectric substrates.
- Voltage from digital to analog converter 808 may be applied to the metallic strips on array of radiating elements 813 through voltage lines 811.
- surface waves propagated across array of radiating elements 813 may be coupled to phase shifter 804 by the surface wave feeds on array of radiating elements 813.
- Phase shifter 804 includes plurality of phase-shifting devices 834.
- a radio frequency module, a phase shifter, and a plurality of surface wave feeds may be present on the opposite side of antenna 802 relative to radio frequency module 806. This configuration may be used in order to facilitate steering in the negative theta direction.
- antenna system 900 may be an example of one implementation for antenna system 100 in Figure 1 .
- Antenna system 900 includes antenna 902, voltage controller 903, phase shifter 904, and radio frequency module 906.
- Voltage controller 903 is configured to supply voltage to antenna 902.
- Voltage controller 903 includes variable voltage source 908.
- Voltage lines 911 apply voltage to antenna 902, while voltage lines 913 provide ground for antenna 902.
- Antenna 902 may include array of radiating elements 915 that may include radiating elements 912, 914, 916, 918, 920, 922, 924, and 926. Each of these radiating elements may be implemented using a dielectric substrate. A surface wave channel may be formed on each radiating element by a plurality of metallic strips, a plurality of varactors, and the dielectric substrate.
- radiating element 912 may be formed using dielectric substrate 927.
- First plurality of metallic strips 928, second plurality of metallic strips 930, and plurality of varactors 932 located on the surface of dielectric substrate 927 may form surface wave channel 931.
- Surface wave feed 933 is also located on the surface of dielectric substrate 927 and couples a surface wave propagated along surface wave channel 931 to phase shifter 904.
- Each of first plurality of metallic strips 928 located on array of radiating elements 915 may have the same width. Further, each of second plurality of metallic strips 930 located on array of radiating elements 915 may have the same width.
- the width of the metallic strips in both first plurality of metallic strips 928 and second plurality of metallic strips 930 varies periodically along dielectric substrate 927 with period, p , 934. This period may be determined by the size of the metallic strips, the radiation frequency, the theta steering angle, and the properties and thickness of dielectric substrate 927.
- any number of metallic strips may be included within a period. Further, any number of different widths may be included within a period.
- Voltage from variable voltage source 908 may be applied to first plurality of metallic strips 928 through voltage lines 911.
- Second plurality of metallic strips 930 may be grounded through voltage lines 913.
- phase shifter 904 includes plurality of phase-shifting devices 936.
- Radio frequency module 906 may be configured to function as a transmitter, a receiver, or a combination of the two.
- FIG. 10 an illustration of antenna system 900 from Figure 9 with a different voltage controller is depicted in accordance with an example.
- voltage controller 903 from Figure 9 has been replaced with voltage controller 1000.
- Voltage controller 1000 includes ground 1002, digital to analog converter 1004, voltage lines 1006, and voltage lines 1008.
- Voltage lines 1006 allow second plurality of metallic strips 930 to be grounded to ground 1002.
- Voltage lines 1008 supply voltage from digital to analog converter 1004 to first plurality of metallic strips 928.
- Controller 1010 is used to control digital to analog converter 1004. In this illustrative example, different voltages are sent to each radiating element in array of radiating elements 915.
- phase shifter 904 is not included in this configuration for antenna system 900.
- Transmission lines 1012 directly couple radio frequency module 906 to the surface wave feeds on array of radiating elements 915.
- the radiation pattern created by antenna 902 is steered in the theta direction by controlling the voltages applied to the different varactors in array of radiating elements 915.
- the radiation pattern created by antenna 902 is steered in the phi direction by the slight variations in surface wave index between neighboring radiating elements. This variation results in phase shifts between the surface waves propagated along these radiating elements, which results in steering in the phi direction.
- phase shifter 904 from Figure 9 has been replaced with phase shifter 1100.
- Phase shifter 1100 may be used to control the phi steering angle for antenna system 900.
- Phase shifter 1100 includes waveguides 1102, 1104, 1106, 1108, 1110, 1112, 1114, and 1116.
- Each of these waveguides is a surface wave waveguide formed by a plurality of metallic strips and a plurality of varactors located on a dielectric substrate. Voltages may be applied to at least a portion of the metallic strips on the different dielectric substrates to control the phase of the surface waves being propagated along these waveguides to steer the radiation towards the phi steering angle.
- the phase of the surface waves may be controlled such that the phase shift of the surface waves at the end of the adjacent waveguides is ⁇ .
- the phase of the surface waves at the end of each of the waveguides is varied by controlling the propagation speed of the surface waves.
- the propagation speed of the surface waves may be controlled by controlling the voltage applied to the varactors on the dielectric substrates.
- Voltage controller 1118 may be used to apply voltages to at least a portion of the metallic strips of the dielectric substrates, and thereby, at least a portion of the varactors on the dielectric substrates.
- Voltage controller 1118 includes digital to analog converter 1120, voltage lines 1122, and ground 1121. Voltages may be applied to at least a portion of the metallic strips on the dielectric substrates from digital to analog converter 1120 by voltage lines 1122. Another portion of the metallic strips may be grounded to ground 1121.
- Controller 1123 may be used to control digital to analog converter 1120.
- Each waveguide may be controlled with a different voltage from voltage controller 1118 in order to create a phase difference at the surface wave feeds on the waveguides.
- the radio frequency signals may be sent between the surface wave feeds and radio frequency module 906 over transmission lines 1124.
- antenna system 1200 is an example of one implementation of antenna system 100 in Figure 1 .
- antenna system 1200 includes radiating element 1201 and radio frequency assembly 1202.
- Radiating element 1201 is an example of one implementation for radiating element 123 in Figure 1 . Further, radiating element 1201 is an example of an implementation for array of radiating elements 122 in Figure 1 comprising only a single radiating element. Only a portion of radiating element 1201 is shown in this illustrative example. In this example, the radiation pattern produced by antenna system 1200 may only be electronically scanned in the X-Z plane.
- radio frequency assembly 1202 includes radio frequency module 1203, phase shifting device 1204, transmission line 1206, transmission line 1208, surface wave feed 1210, and surface wave feed 1211.
- Radio frequency module 1203 may be configured to function as a transmitter, a receiver, or a combination of the two.
- Phase shifting device 1204 takes the form of a hybrid power splitter in this example.
- the hybrid power splitter is configured for use in varying the phase difference between the radio frequency signal traveling along transmission line 1206 and the radio frequency signal traveling along transmission line 1208.
- the hybrid power splitter may be used to vary the phase difference between these two transmission lines between about 0 degrees and about 90 degrees.
- radio frequency module 1203 and phase shifting device 1204 may be implemented in some other manner.
- radio frequency module 1203 may be configured to enable dual polarization with phase shifting device 1204 taking the form of a four port variable phase power splitter.
- Radiating element 1201 is implemented using dielectric substrate 1205.
- Surface wave channel 1212 and surface wave channel 1213 are formed on dielectric substrate 1205.
- Surface wave feed 1210 couples transmission line 1206 to surface wave channel 1212.
- Surface wave feed 1211 couples transmission line 1208 to surface wave channel 1213.
- Surface wave channel 1212 and surface wave channel 1213 may be examples of implementations for surface wave channel 125 and second surface wave channel 145 in Figure 1 .
- surface wave channel 1212 is formed by plurality of metallic strips 1214 and plurality of varactors 1215.
- plurality of metallic strips 1214 are periodically arranged at an angle of about positive 45 degrees relative to X-axis 1216.
- X-axis 1216 is the longitudinal axis along radiating element 1201.
- Plurality of varactors 1215 are electrically connected to plurality of metallic strips 1214.
- Voltage lines 1218 are used to apply voltages to plurality of varactors 1215.
- Pins 1220 may be used to connect voltage lines 1218 to one or more voltage sources and/or one or more grounds.
- surface wave channel 1213 is formed by plurality of metallic strips 1224 and plurality of varactors 1226. As depicted, plurality of metallic strips 1224 are periodically arranged at an angle of about negative 45 degrees relative to X-axis 1216. Voltage lines 1228 are used to apply voltages to plurality of varactors 1226. Pins 1230 are used to connect voltage lines 1228 to one or more voltage sources and/or one or more grounds.
- the radiation pattern formed by radiating element 1201 may be scanned in the X-Z plane by changing the voltages applied to plurality of varactors 1215 such that the surface wave impedance modulation pattern results in the desired radiation angle.
- Surface wave channel 1212 and surface wave channel 1213 are configured such that the radiation from these two surface wave channels may be orthogonal to each other. The net radiation from the combination of these two surface wave channels is circularly polarized.
- phase shifting device 1204 When fed by phase shifting device 1204 in the form of a 0°-90° hybrid splitter, surface wave channel 1212 and surface wave channel 1213 are fixed into receiving or transmitting circularly-polarized radiation with either right-hand polarization or left-hand polarization.
- phase shifting device 1204 may be implemented in some other manner such that the radiation may be switched between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP).
- the radiation from surface wave channel 1212 and surface wave channel 1213 is polarized because of the angles at which plurality of metallic strips 1214 and plurality of metallic strips 1224, respectively, are tilted relative to X-axis 1216.
- Plurality of metallic strips 1214 and plurality of metallic strips 1224 are tensor impedance elements having a major principal axis that is perpendicular to the long edges of the metallic strips and a minor axis that is along the edges.
- the radiation is driven by the surface wave currents according to the following equation: E rad ⁇ ⁇ k ⁇ ⁇ J sw ⁇ k ⁇ e ⁇ i k ⁇ r ′ dx e i k ⁇ r , and is therefore polarized in the direction across the gaps between the metallic strips.
- E rad is the electric field of the radiation.
- FIG. 13 an illustration of antenna system 1200 from Figure 12 having two radio frequency assemblies is depicted in accordance with an example.
- radio frequency assembly 1202 is located at end 1300 of radiating element 1201, while radio frequency assembly 1301 is located at end 1303 of radiating element 1201.
- Radio frequency assembly 1301 includes radio frequency module 1302, phase shifting device 1304, transmission line 1306, transmission line 1308, surface wave feed 1310, and surface wave feed 1312.
- Surface wave feed 1310 feeds into surface wave channel 1212. Further, surface wave feed 1312 feeds into surface wave channel 1213.
- Radio frequency assembly 1301 or radio frequency assembly 1202 may function as a sink for any surface wave energy that is not radiated away. In this manner, surface waves may be prevented from reflecting off at the end of radiating element 1201, which would lead to undesired distortion of the radiation pattern.
- the radiation pattern may be more effectively tuned over a larger angular range.
- radio frequency assembly 1202 may be used to feed the radio frequency signal to radiating element 1201.
- radio frequency assembly 1301 may be used to feed the radio frequency signal to radiating element 1201. In this manner, as the radio frequency beam formed by the radiation pattern is scanned in an angle, beams directed with angles of positive theta and negative theta may be mirror images of each other.
- antenna system 1400 is another example of one implementation for antenna system 100 in Figure 1 .
- Antenna system 1400 includes antenna 1401, phase shifter 1402, and radio frequency module 1404.
- Antenna system 1400 may also include a voltage controller (not shown in this example).
- Antenna 1401 includes array of radiating elements 1406 and plurality of surface wave feeds 1407.
- Array of radiating elements 1406 includes radiating elements 1408, 1410, 1412, 1414, 1416, 1418, 1420, and 1422. Each of these radiating elements may be implemented in a manner similar to radiating element 1201 in Figure 12 .
- Phase shifter 1402 includes plurality of phase-shifting devices 1424.
- Transmission lines 1426 connect plurality of surface wave feeds 1407 to plurality of phase-shifting devices 1424 and connect plurality of phase-shifting devices 1424 to radio frequency module 1404.
- Radio frequency module 1404 may be configured to function as a transmitter, a receiver, or a combination of the two.
- Plurality of phase-shifting devices 1424 are variable phase shifters in this example.
- plurality of phase-shifting devices 1424 may be tuned such that the net phase shift at each one of plurality of surface wave feeds 1407 differs from the phase at a neighboring surface wave feed by a constant, ⁇ . As this constant is varied, the radiation pattern formed may be scanned in the Y-Z plane.
- FIG. 2-14 may be illustrative examples of how components shown in block form in Figure 1 can be implemented as physical structures. Additionally, some of the components in Figures 2-14 may be combined with components in Figure 1 , used with components in Figure 1 , or a combination of the two.
- an antenna such as artificial impedance surface antenna 110 in Figure 1 .
- the gain of an artificial impedance surface antenna may be improved by improving the accuracy with which the artificial impedance surface antenna is electronically steered to reduce fall off in gain.
- the illustrative examples recognize and take into account that a substantially, radially symmetric arrangement of surface wave channels may allow more accurate electronic steering of the artificial impedance surface antenna. Further, with this type of arrangement, the impedance elements used to form the surface wave channels may be spaced apart greater than half a wavelength. Still further, this type of arrangement may be used to produce radiation of any polarization.
- FIG. 15 an illustration of a different configuration for artificial impedance surface antenna 110 in antenna system 100 from Figure 1 is depicted in the form of a block diagram in accordance with an example.
- Antenna system 100 from Figure 1 is depicted with artificial impedance surface antenna 110 having radial configuration 1500.
- artificial impedance surface antenna 110 When artificial impedance surface antenna 110 has radial configuration 1500, artificial impedance surface antenna 110 includes dielectric substrate 1501, plurality of radiating spokes 1502, and number of surface wave feeds 1504.
- Dielectric substrate 1501 may be implemented in a manner similar to dielectric substrate 124 in Figure 1 . However, with radial configuration 1500, dielectric substrate 1501 may be the only dielectric substrate used. Dielectric substrate 1501 may be comprised of any number of layers of dielectric material.
- dielectric substrate 1501 may be comprised of a material with tunable electrical properties.
- dielectric substrate 1501 may be comprised of a liquid crystal material.
- dielectric substrate 1501 has circular shape 1506 with center point 1508. In other words, dielectric substrate 1501 may be substantially symmetric about center point 1508. In other illustrative examples, dielectric substrate 1501 may have some other shape. For example, without limitation, dielectric substrate 1501 may have an oval shape, a square shape, a hexagonal shape, an octagonal shape, or some other type of shape. However, when dielectric substrate 1501 is not substantially symmetric about center point 1508, the radiation pattern 112 produced may not have the same gain at different steering angles.
- plurality of radiating spokes 1502 may be implemented using dielectric substrate 1501.
- plurality of radiating spokes 1502 may be formed on dielectric substrate 1501.
- Plurality of radiating spokes 1502 may be arranged radially with respect to center point 1508 of dielectric substrate 1501.
- being arranged radially with respect to center point 1508 means that each of plurality of radiating spokes 1502 may extend from center point 1508 towards an outer circumference of dielectric substrate 1501.
- Each of plurality of radiating spokes 1502 may be arranged substantially perpendicular to a center axis through center point 1508 of dielectric substrate 1501. Further, each of plurality of radiating spokes 1502 may be arranged in a manner such that each radiating spoke is substantially symmetric about center point 1508.
- Each of plurality of radiating spokes 1502 may be implemented in a manner similar to radiating element 123 from Figure 1 .
- Radiating spoke 1510 may be an example of one implementation for each radiating spoke in plurality of radiating spokes 1502.
- Radiating spoke 1510 is configured to form surface wave channel 1512. In this manner, plurality of radiating spokes 1502 may form a plurality of surface wave channels.
- Surface wave channel 1512 is configured to constrain a path of a surface wave.
- radiating spoke 1510 may include plurality of impedance elements 1514 and plurality of tunable elements 1516.
- Plurality of impedance elements 1514 and plurality of tunable elements 1516 may be implemented in a manner similar to plurality of impedance elements 126 and plurality of tunable elements 128, respectively, from Figure 1 .
- plurality of impedance elements 1514 and plurality of tunable elements 1516 may be located on surface 1513 of dielectric substrate 1501.
- plurality of impedance elements 1514 and plurality of tunable elements 1516 may be located on surface 1513 of corresponding portion 1515 of dielectric substrate 1501.
- Plurality of impedance elements 1514, plurality of tunable elements 1516, and corresponding portion 1515 of dielectric substrate 1501 may form an artificial impedance surface from which radiation may be generated.
- corresponding portion 1515 of dielectric substrate 1501 may be considered part of radiating spoke 1510.
- dielectric substrate 1501 may be considered separate from plurality of radiating spokes 1502.
- An impedance element in plurality of impedance elements 1514 may be implemented in a number of different ways.
- an impedance element may be implemented as a resonating element.
- an impedance element may be implemented as an element comprised of a conductive material.
- the conductive material may be, for example, without limitation, a metallic material.
- an impedance element may be implemented as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate, or some other type of conductive element.
- an impedance element may be implemented as a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element.
- a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element.
- Each one of plurality of tunable elements 1516 may be an element that can be controlled, or tuned, to change an angle of radiation pattern 112 produced by radiating spoke 1510.
- each of plurality of tunable elements 1516 may be an element having a capacitance that can be varied based on the voltage applied to the tunable element.
- plurality of impedance elements 1514 takes the form of plurality of metallic strips 1518 and plurality of tunable elements 1516 takes the form of plurality of varactors 1520.
- Each of plurality of varactors 1520 may be a semiconductor element diode that has a capacitance dependent on the voltage applied to the semiconductor element diode.
- Plurality of metallic strips 1518 may be arranged in a row on corresponding portion 1515 of dielectric substrate 1501 substantially parallel to a plane that is substantially perpendicular to a center axis through center point 1508 of dielectric substrate 1501.
- plurality of metallic strips 1518 may be periodically distributed on corresponding portion 1515 of dielectric substrate 1501 along an axis that is substantially perpendicular to and that passes through the center axis through dielectric substrate 1501.
- plurality of metallic strips 1518 may be printed onto dielectric substrate 1501.
- plurality of metallic strips 1518 may be printed onto dielectric substrate 1501 using any number of three-dimensional printing techniques, additive deposition techniques, inkjet deposition techniques, or other types of printing techniques.
- Plurality of varactors 1520 may be electrically connected to plurality of metallic strips 1518 on surface 1513 of corresponding portion 1515 of dielectric substrate 1501.
- at least one varactor in plurality of varactors 1520 may be positioned between each adjacent pair of metallic strips in plurality of metallic strips 1518. Further, plurality of varactors 1520 may be aligned such that all of the varactor connections on each metallic strip have the same polarity.
- Voltages may be applied to plurality of tunable elements 1516 by applying voltages to plurality of impedance elements 1514.
- varying the voltages applied to plurality of impedance elements 1514 varies the capacitance of plurality of tunable elements 1516.
- Varying the capacitances of plurality of tunable elements 1516 may vary, or modulate, the capacitive coupling and impedance between plurality of impedance elements 1514.
- Corresponding portion 1515 of dielectric substrate 1501, plurality of impedance elements 1514, and plurality of tunable elements 1516 may be configured with respect to selected design configuration 1522 for surface wave channel 1512 formed by radiating spoke 1510.
- each radiating spoke in plurality of radiating spokes 1502 may have a same or different selected design configuration.
- selected design configuration 1522 for radiating spoke 1510 may include a number of design parameters such as, but not limited to, impedance element width 1524, impedance element spacing 1526, tunable element spacing 1528, and substrate thickness 1530.
- Impedance element width 1524 may be the width of an impedance element in plurality of impedance elements 1514. Impedance element width 1524 may be selected to be the same or different for each of plurality of impedance elements 1514, depending on the implementation.
- Impedance element spacing 1526 may be the spacing of plurality of impedance elements 1514 along surface 1513 of corresponding portion 1515 of dielectric substrate 1501.
- Tunable element spacing 1528 may be the spacing of plurality of tunable elements 1516 along surface 1513 of corresponding portion 1515 of dielectric substrate 1501.
- substrate thickness 1530 may be the thickness of corresponding portion 1515 of dielectric substrate 1501.
- an entirety of dielectric substrate 1501 may have a substantially same thickness.
- the different portions of dielectric substrate 1501 corresponding to the different radiating spokes in plurality of radiating spokes 1502 may have different thicknesses.
- the values for the different parameters in selected design configuration 1522 may be selected based on, for example, without limitation, the radiation frequency at which artificial impedance surface antenna 110 is configured to operate. Other considerations include, for example, the desired impedance modulations for artificial impedance surface antenna 110.
- the surface waves propagated along each of plurality of radiating spokes 1502 may be coupled to number of transmission lines 156 by number of surface wave feeds 1504 located on dielectric substrate 1501.
- Each of number of surface wave feeds 1504 couples at least one corresponding radiating spoke in plurality of radiating spokes 1502 to a transmission line that carries a radio frequency signal, such as one of number of transmission lines 156.
- a surface wave feed in number of surface wave feeds 1504 may be any device that is capable of converting a surface wave into a radio frequency signal, a radio frequency signal into a surface wave, or both.
- a surface wave feed in number of surface wave feeds 1504 may be located substantially at center point 1508 of dielectric substrate 1501.
- number of surface wave feeds 1504 takes the form of a single surface wave feed positioned at center point 1508 of dielectric substrate 1501.
- This single surface wave feed which may be referred to as a central feed, may couple each of plurality of radiating spokes 1502 to number of transmission lines 156.
- number of transmission lines 156 may take the form of a coaxial cable.
- number of surface wave feeds 1504 may take the form of a plurality of surface wave feeds located at or near center point 1508 and configured to couple plurality of radiating spokes 1502 to number of transmission lines 156.
- number of transmission lines 156 may take the form of a single transmission line or a plurality of transmission lines.
- electromagnetic radiation received at artificial impedance surface antenna 110 may be propagated as surface waves along plurality of radiating spokes 1502. These surface waves are received by number of surface wave feeds 1504 and converted into number of radio frequency signals 1532. Number of radio frequency signals 1532 may be sent to radio frequency module 108 over one or more of number of transmission lines 156. Radio frequency module 108 may then process number of radio frequency signals 1532 accordingly.
- number of radio frequency signals 1532 may be sent from radio frequency module 108 to artificial impedance surface antenna 110 over number of transmission lines 156.
- number of radio frequency signals 1532 may be received at number of surface wave feeds 1504 and converted into surface waves that are propagated along plurality of radiating spokes 1502.
- Radiation pattern 112 of artificial impedance surface antenna 110 may be electronically steered in both a theta direction and a phi direction. Radiation pattern 112 may be formed by number of radiation sub-patterns 1533. Number of radiation sub-patterns 1533 may be produced by a corresponding portion of plurality of radiating spokes 1502. This corresponding portion may be one or more of plurality of radiating spokes 1502. In some cases, number of radiation sub-patterns 1533 may be produced by all of plurality of radiating spokes 1502.
- number of radiation sub-patterns 1533 may be produced by a corresponding number of radiating spokes in plurality of radiating spokes 1502. Each of number of radiation sub-patterns 1533 is the radiation pattern produced by a particular radiating spoke. Number of radiating sub-patterns 1533 forms radiation pattern 112. For example, when number of radiating sub-patterns 1533 includes multiple radiating sub-patterns corresponding to multiple radiating spokes, the combination and overlapping of these multiple radiation sub-patterns forms radiation pattern 112.
- each of plurality of radiating spokes 1502 may be independently controlled such that each of number of radiation sub-patterns 1533 may be electronically steered.
- radiating spoke 1510 may have radiation sub-pattern 1534.
- Radiation sub-pattern 1534 may be controlled independently of the other radiation sub-patterns formed by the other radiating spokes in plurality of radiating spokes 1502.
- voltage controller 104 may be used to control the voltages applied to plurality of tunable elements 1516 to control both the theta and phi steering angles of a main lobe of radiation sub-pattern 1534.
- voltage controller 104 may be configured to control the voltages applied to the plurality of tunable elements in each of plurality of radiating spoke 1502 to control both the theta and phi steering angles of a main lobe of the radiation sub-pattern formed by each of plurality of radiating spokes 1502.
- each of number of radiation sub-patterns 1533 may be directed in a particular theta direction and a broad phi direction.
- a particular radiation sub-pattern may be directed at a theta steering angle of about 45 degrees and may fan out over a broad range of phi angles.
- each radiation sub-pattern may form, for example, a fan beam.
- Radiation pattern 112 may be formed such that a beam of radiation is produced.
- the beam may take the form of, for example, a pencil beam that is directed at a particular phi steering angle 118 and a particular theta steering angle 120.
- artificial impedance surface antenna 110 may be electronically steered in two dimensions.
- artificial impedance surface antenna 110 may be configured to emit linearly polarized radiation or circularly polarized radiation.
- artificial impedance surface antenna 110 may be used to produce radiation pattern 112 that is linearly polarized or circularly polarized.
- radiation pattern 112 may be switched between being linearly polarized and circularly polarized by adjusting the voltages applied to plurality of tunable elements 1516 and without needing to change a physical configuration of artificial impedance surface antenna 110.
- the impedance sub-patterns produced by the surface wave channels formed by plurality of radiating spokes 1502 may be modulated to produce overall radiation pattern 112 that is linearly polarized.
- ⁇ 0 is the theta angle of the main lobe of the radiation pattern
- ⁇ 0 is the phi angle of the main lobe of the radiation pattern
- ⁇ swc is the polar angle of the line that extends along a center of the surface wave channel
- r is the radial distance along the surface wave channels
- X and M are the mean impedance and the amplitude, respectively,
- the impedance sub-patterns of the surface wave channels formed by plurality of radiating spokes 1502 may be modulated to produce overall radiation pattern 112 that is circularly polarized.
- the impedance sub-patterns may be given by other types of equations involving periodic functions.
- the sine function of sin( ⁇ ⁇ ⁇ ) in Equation (19) the sine function of sin( ⁇ ⁇ ⁇ 0 ) in Equation (15), and the cosine function of cos( k 0 r ( n 0 -cos( ⁇ swc - ⁇ 0 )sin( ⁇ 0 )) in Equation (13) may each be replaced by some other type of periodic function.
- artificial impedance surface antenna 110 may be used to produce radiation of any polarization without requiring a change in the physical configuration of artificial impedance surface antenna 110.
- Artificial impedance surface antenna 110 may be used to produce linearly polarized or circularly polarized radiation just by changing the voltages applied to the tunable elements of plurality of radiating spokes 1502.
- artificial impedance surface antenna 110 may propagate surface waves towards or away from center point 1508 of dielectric substrate 1501.
- artificial impedance surface antenna 110 may include absorption material 1536 when the surface waves are propagated away from center point 1508.
- Absorption material 1536 may be located at and around an edge of dielectric substrate 1501.
- Absorption material 1536 is configured to absorb excess energy from the surface waves propagated radially outward away from center point 1508 through plurality of radiating spokes 1502.
- dielectric substrate 1501 may be grounded using grounding element 1538.
- grounding element 1538 may be located at an impedance surface of dielectric substrate 1501.
- antenna system 100 in Figure 1 is not meant to imply physical or architectural limitations to the manner in which an illustrative example may be implemented.
- Other components in addition to or in place of the ones illustrated may be used. Some components may be optional.
- the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative example.
- a tunable element in plurality of tunable elements 1516 may be implemented as a pocket of variable material embedded in dielectric substrate 1501.
- a tunable element in plurality of tunable elements 1516 may be part of a corresponding impedance element in plurality of impedance elements 1514.
- a resonant structure having a tunable element may be used.
- the resonant structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled resonator, or some other type of resonant structure.
- center point 1508 may be the center point about which plurality of radiating spokes 1502 are arranged but may not be the geometric center of dielectric substrate 1501.
- center point 1508 may be offset from the geometric center of dielectric substrate 1501.
- each of plurality of radiating spokes 1502 may have two independently controllable portions configured to form a surface wave channel.
- radiating spoke 1510 may have a first portion that extends in one direction away from center point 1508 and a second portion that extends in the substantially opposite direction away from center point 1508. These two portions may have a same or different design configuration, depending on the implementation. Further, these two portions may be individually referred to as radiating spokes or radiating sub-spokes in some cases.
- Figure 16 an illustration of an artificial impedance surface antenna is depicted in accordance with an example.
- artificial impedance surface antenna 1600 may be an example of one implementation for artificial impedance surface antenna 110 having radial configuration 1500 in Figure 15 .
- Artificial impedance surface antenna 1600 has radial configuration 1601, which may be an example of one implementation for radial configuration 1500 in Figure 15 .
- artificial impedance surface antenna 1600 includes dielectric substrate 1602, central surface wave feed 1604, and plurality of radiating spokes 1606.
- Dielectric substrate 1602, central surface wave feed 1604, and plurality of radiating spokes 1606 may be examples of implementations for dielectric substrate 1501, number of surface wave feeds 1504, and plurality of radiating spokes 1502, respectively, in Figure 15 .
- dielectric substrate 1602 has a circular shape with center point 1605.
- Plurality of radiating spokes 1606 are arranged radially with respect to center point 1605 such that artificial impedance surface antenna 1600 is substantially radially symmetric.
- Radiating spoke 1608, radiating spoke 1610, radiating spoke 1612, and radiating spoke 1614 may be examples of some of plurality of radiating spokes 1606.
- Plurality of radiating spokes 1606 are formed by impedance elements 1616 that have been printed on dielectric substrate 1602. Impedance elements 1616 take the form of metallic strips in this illustrative example.
- Plurality of radiating spokes 1606 may also include tunable elements (not shown in this view) located between impedance elements 1616.
- Central surface wave feed 1604 may couple plurality of radiating spokes 1606 to a transmission line (not shown in this view).
- the transmission line may be configured to carry a radio frequency to, from, or both to and from central surface wave feed 1604.
- Artificial impedance surface antenna 1600 may be electronically steered with a desired level of accuracy in a theta direction and a phi direction.
- Each of plurality of radiating spokes 1606 may be individually electronically steered in a particular theta direction and a broad phi direction to produce a fan beam.
- radiating spoke 1608, radiating spoke 1612, and radiating spoke 1614 may be electronically steered to produce fan beam 1618, fan beam 1620, and fan beam 1622, respectively.
- the radiation patterns corresponding to fan beam 1618, fan beam 1620, and fan beam 1622 may overlap such that pencil beam 1624 is produced.
- Pencil beam 1624 may be directed at a particular theta steering angle and a particular phi steering angle.
- absorption material 1626 is located at and around an outer edge of dielectric substrate 1602.
- Absorption material 1626 may be an example of one implementation for absorption material 1536 in Figure 15 .
- Absorption material 1626 is configured to absorb excess energy resulting from surface waves propagating away from center point 1605.
- Figure 17 an illustration of a cross-sectional side view of artificial impedance surface antenna 1600 from Figure 16 is depicted in accordance with an illustrative example.
- a cross-sectional side view of artificial impedance surface antenna 1600 from Figure 16 is depicted taken with respect to cross-section lines 17-17 in Figure 17 .
- grounding element 1700 may be seen along the surface of dielectric substrate 1602.
- Grounding element 1700 is an example of one implementation for grounding element 1538 in Figure 15 .
- Transmission line 1702 is also shown in this view.
- Transmission line 1702 may carry a radio frequency to, from, or both to and from central surface wave feed 1604.
- transmission line 1702 takes the form of a coaxial cable.
- surface waves may propagate in the direction of arrow 1704, substantially parallel to dielectric substrate 1602 and substantially perpendicular to center axis 1706 through center point 1605 of dielectric substrate 1602.
- Plurality of radiating spokes 1606 may be arranged such that plurality of radiating spokes 1606 are substantially symmetric about center axis 1706.
- FIG. 18 an illustration of an impedance pattern for artificial impedance surface antenna 1600 from Figures 16-17 is depicted in accordance with an example.
- impedance pattern 1800 may be produced when artificial impedance surface antenna 1600 is linearly polarized and configured to produce a radiation pattern having a main lobe directed at a theta steering angle of about 45 degrees and a phi steering angle of about 0 degrees.
- Impedance pattern 1800 is shown with respect to first axis 1802 and second axis 1804.
- First axis 1802 and second axis 1804 may represent the two axes that form the plane substantially parallel to dielectric substrate 1602 in Figure 16 .
- Impedance pattern 1800 is comprised of impedance sub-patterns 1806 formed by plurality of radiating spokes 1606 in Figures 16 .
- Scale 1808 provides the correlation between the impedance sub-patterns 1806 and impedance values.
- the impedance values may be in units of j-Ohms in which j is equal to ⁇ 1 .
- artificial impedance surface antenna 1900 may be another example of one implementation for artificial impedance surface antenna 110 having radial configuration 1500 in Figure 15 .
- Artificial impedance surface antenna 1900 has radial configuration 1901, which may be an example of one implementation for radial configuration 1500 in Figure 15 .
- artificial impedance surface antenna 1900 includes dielectric substrate 1902, radiating spokes 1904, and central surface wave feed 1906. Only a portion of the total plurality of radiating spokes that form artificial impedance surface antenna 1900 are shown in this view.
- Radiating spoke 1907 is an example of one of radiating spokes 1904. Only a portion of radiating spoke 1907 is shown. Radiating spoke 1907 is located on corresponding portion 1908 of dielectric substrate 1902. Radiating spoke 1907 includes plurality of metallic strips 1909 and plurality of varactors 1910. Plurality of metallic strips 1909 and plurality of varactors 1910 may be an example of one implementation for plurality of metallic strips 1518 and plurality of varactors 1520, respectively, in Figure 15 .
- voltages may be applied to plurality of metallic strips 1909, and thereby plurality of varactors 1910, through conductive lines 1912, which terminate at terminals 1914.
- Terminals 1914 may be connected to electrical vias (not shown in this view) that pass through the thickness of dielectric substrate 1902 and through a grounding element (not shown in this view) to connectors that connect to control hardware, such as a voltage controller.
- FIG. 20 an illustration of a cross-sectional side view of artificial impedance surface antenna 1900 from Figure 19 is depicted in accordance with an example.
- FIG. 19 a cross-sectional side view of artificial impedance surface antenna 1900 from Figure 19 is depicted taken with respect to cross-section lines 20-20 in Figure 19 .
- Voltage controller 2002 may vary the voltages applied to the metallic strips of plurality of radiating spokes 1904 in Figure 19 .
- the illustrative embodiments recognize and take into account that different types of configurations for artificial impedance surface antenna 110 in Figure 1 may improve the efficiency and thereby, overall performance, of artificial impedance surface antenna 110.
- the illustrative embodiments recognize and take into account that in some cases, it may be desirable to provide a square-wave-type profile of surface impedance across each surface wave channel formed on each radiating element of artificial impedance surface antenna 110 in Figure 1 .
- switch elements that have only two possible states as compared to varactors that can be tuned to have any of various capacitance states across a range of capacitance values may enable achieving a square-wave-type profile of surface impedance for a surface wave channel.
- These switch elements may take the form of, for example, without limitation, PIN diodes.
- FIG. 21 an illustration of artificial impedance surface antenna 110 from Figure 1 is depicted in the form of a block diagram in accordance with an illustrative embodiment.
- at least one surface wave channel on at least one radiating element in artificial impedance surface antenna 110 in Figure 21 is implemented differently than as described in Figure 1 .
- surface wave channel 125 from Figure 1 does not include plurality of tunable elements 128 from Figure 1 .
- surface wave channel 125 includes plurality of switch elements 2100 instead of plurality of tunable elements 128 from Figure 1 .
- Each of plurality of switch elements 2100 has only two states 2102.
- Two states 2102 may include first state 2104 and second state 2106.
- first state 2104 may be referred to as an on state and second state 2106 may be referred to as an off state.
- plurality of switch elements 2100 takes the form of plurality of PIN diodes 2108.
- a switch element in plurality of switch elements 2100 is selected from one of a semiconductor switch, a microelectromechanical systems (MEMS) switch, a high frequency diode, a Schottky diode, and a phase-change material switch.
- MEMS microelectromechanical systems
- Switch element 2101 may be an example of one of plurality of switch elements 2100.
- Switch element 2101 is placed within the gap between first impedance element 2113 of plurality of impedance elements 126 and second impedance element 2115 of plurality of impedance elements 126. Further, switch element 2101 electrically connects first impedance element 2113 to second impedance element 2115. The capacitance of switch element 2101 and the capacitance of the gap between first impedance element 2113 and second impedance element 2115 contribute to the total capacitance between first impedance element 2113 and second impedance element 2115. In some cases, the capacitance of the gap between first impedance element 2113 and second impedance element 2115 may be negligible.
- first state 2104 may take the form of inductance state 2105 and second state 2106 may take the form of capacitance state 2107.
- Switch element 2101 may be placed in inductance state 2105 by applying a first level of voltage to switch element 2101.
- Switch element 2101 may be placed in capacitance state 2107 by applying a second level of voltage to switch element 2101.
- switch element 2101 is in inductance state 2105 or in capacitance state 2107 may be determined by the reactance of switch element 2101.
- the resistance may also be referred to as surface resistance and the reactance may also be referred to as surface reactance.
- the reactance is positive, the reactance is described as inductive and switch element 2101 may be considered in inductance state 2105.
- the reactance is negative, the reactance is described as capacitive and switch element 2101 may be considered in capacitance state 2107.
- the reactance is substantially zero, the surface impedance may be considered substantially purely resistive.
- switch element 2101 may have substantially zero capacitance but may have parasitic inductance. In other words, the capacitance of switch element 2101 may be zero or negligible when switch element 2101 is in inductance state 2105. In this manner, in inductance state 2105, switch element 2101 may be modeled as a series resistor-inductor circuit. In capacitance state 2107, switch element 2101 may have some selected non-zero capacitance value. In this manner, in capacitance state 2107, switch element 2101 may be modeled as a parallel resistor-capacitor circuit.
- each of plurality of switch elements 2100 may have only one of two states 2102 at any given point in time
- the voltages applied to plurality of switch elements 2100 may be used to create surface impedance profile 2114 for surface wave channel 125.
- one of two levels of voltage may be applied to each of plurality of switch elements 2100 to create surface impedance profile 2114.
- Surface impedance profile 2114 may be created such that only a selected high surface impedance, a selected low surface impedance, or some combination of the two is formed.
- the voltages applied to plurality of switch elements 2100 may be controlled such that surface impedance profile 2114 takes the form of square-wave modulation 2110 of high surface impedance and low surface impedance.
- Square-wave modulation 2110 may be a square-wave-type modulation.
- the state of each of plurality of switch elements 2100 may be controlled to modulate high surface impedance and low surface impedance in the form of a square-wave as compared to a sinusoidal wave.
- These two surface impedance levels may be modulated over each surface wave channel on each radiating element of artificial impedance surface antenna 110 to electronically steer artificial impedance surface antenna 110 in a theta direction, a phi direction, or both.
- each of plurality of impedance elements 126 may take the form of a rectangular metallic strip.
- each of plurality of impedance elements 126 has a shape that has repeating pattern 2112.
- Repeating pattern 2112 may be a pattern of shapes.
- a particular impedance element of plurality of impedance elements 126 has a repeating pattern of a same shape that hexagonal-type shape.
- the shape may be a diamond-type shape, or some other type of shape.
- Using plurality of switch elements 2100 for surface wave channel 125 may improve the gain of artificial impedance surface antenna 110. Further, using plurality of switch elements 2100 may enable artificial impedance surface antenna 110 to be operated at a frequency in the Ka-band with a desired level of aperture efficiency. In this manner, using plurality of switch elements 2100 may reduce power loss.
- the Ka-band may include frequencies between about 26.5 gigahertz and about 40 gigahertz.
- using plurality of PIN diodes 2108 may enable artificial impedance surface antenna 110 to be operated at a frequency of about 30 gigahertz with greater than about 25 percent aperture efficiency.
- artificial impedance surface antenna 110 in Figure 21 is not meant to imply physical or architectural limitations to the manner in which an illustrative embodiment may be implemented.
- Other components in addition to or in place of the ones illustrated may be used. Some components may be optional.
- the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative embodiment.
- radiating element 2200 is one implementation for radiating element 123 in Figure 21 .
- radiating element 2200 includes dielectric substrate 2202.
- Surface wave channel 2204 is formed on dielectric substrate 2202.
- Surface wave channel 2204 is one implementation for surface wave channel 125 in Figure 21 .
- surface wave channel 2204 comprises plurality of impedance elements 2206 and plurality of switch elements 2208.
- plurality of switch elements 2208 are one implementation for plurality of switch elements 2100 in Figure 21 .
- Each of plurality of switch elements 2208 has only one of two states at any given point in time in this illustrative embodiment.
- the switch element when one of plurality of switch elements 2208 is in an on state, the switch element may function in a manner similar to a circuit comprising a resistor and inductor in series.
- the on state corresponds to high surface impedance.
- the inductance that is provided may be important to enable operation of the artificial surface impedance antenna to which surface wave channel 2204 belongs within the Ka-band of frequencies.
- the switch element When the switch element is in an off state, the switch element may function in a manner similar to a circuit comprising a resistor and capacitor in parallel. The off state corresponds to low surface impedance.
- each of plurality of switch elements 2208 is controlled to modulate between high surface impedance and low surface impedance to create a surface impedance profile for surface wave channel 2204.
- This surface impedance profile may resemble a square-wave-type modulation.
- Portion 2210 of surface wave channel 2204 is shown enlarged in Figure 23 below.
- plurality of impedance elements 2206 includes impedance element 2300 and impedance element 2302.
- Impedance element 2300 and impedance element 2302 are implementations for first impedance element 2113 and second impedance element 2115, respectively, from Figure 21 .
- Plurality of switch elements 2208 includes set of switch elements 2304 positioned within the gap between impedance element 2300 and impedance element 2302.
- Each of set of switch elements 2304 has only two possible states and may be in only one of these two possible states at any given point in time. In one illustrative example, these two states may be an inductance state and a capacitance state.
- set of switch elements 2304 includes switch element 2306, switch element 2308, and switch element 2310.
- Switch element 2306, switch element 2308, and switch element 2310 electrically connect impedance element 2300 and impedance element 2302.
- Each of plurality of impedance elements 2206 in Figure 22 has a repeating pattern of shapes.
- Impedance element 2302 has repeating pattern 2312.
- Repeating pattern 2312 is a series of same shapes.
- Repeating pattern 2312 is a series of hexagonal-type shapes. As depicted, repeating pattern 2312 includes hexagonal-type shape 2314, hexagonal-type shape 2316, and hexagonal-type shape 2318.
- radiating element 2400 may be an example of one implementation for radiating element 123 in Figure 21 .
- radiating element 2400 includes dielectric substrate 2402.
- Surface wave channel 2404 is formed on dielectric substrate 2402.
- Surface wave channel 2404 may be an example of one implementation for surface wave channel 125 in Figure 21 .
- Surface wave channel 2404 comprises plurality of impedance elements 2406 and plurality of switch elements 2408.
- Plurality of impedance elements 2406 may be an example of one implementation for plurality of impedance elements 126 in Figure 1 .
- each of plurality of impedance elements 2406 may take the form of a rectangular metallic strip.
- Plurality of switch elements 2408 may be an example of one implementation for plurality of switch elements 2100 in Figure 21 .
- each of plurality of switch elements 2408 may have only one of two states at any given point in time.
- each of plurality of switch elements 2408 may be implemented in the form of a PIN diode.
- the switch element when one of plurality of switch elements 2408 is in an on state, the switch element may function in a manner similar to a circuit comprising a resistor and inductor in series.
- the on state corresponds to high surface impedance.
- the inductance that is provided may be important to enable operating within the Ka-band of frequencies.
- the switch element When the switch element is in an off state, the switch element may function in a manner similar to a circuit comprising a resistor and capacitor in parallel. The off state corresponds to low surface impedance.
- FIG. 25 an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative example.
- the process illustrated in Figure 25 may be implemented to electronically steer antenna system 100 in Figure 1 .
- the process begins by propagating a surface wave along each of a number of surface wave channels formed in each of a plurality of radiating elements to form a radiation pattern (operation 2500 ).
- Each surface wave channel in the number of surface wave channels formed in each radiating element in the plurality of radiating elements is coupled to a transmission line configured to carry a radio frequency signal using a surface wave feed in a plurality of surface wave feeds associated with the plurality of radiating elements (operation 2502 ).
- a main lobe of the radiation pattern is electronically steered in a theta direction by controlling voltages applied to the number of surface wave channels in each radiating element in the plurality of radiating elements (operation 2504 ). Further, the main lobe of the radiation pattern is electronically steered in a phi direction by controlling a relative phase difference between the plurality of surface wave feeds (operation 2506 ), with the process terminating thereafter.
- FIG. 26 an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative example.
- the process illustrated in Figure 26 may be implemented to electronically steer, for example, artificial impedance surface antenna 110 having radial configuration 1500 in Figure 15 .
- the process begins by propagating a surface wave along a plurality of surface wave channels formed by a plurality of radiating spokes in an antenna to generate a number of radiation sub-patterns in which the plurality of radiating spokes is arranged radially with respect to a center point of a dielectric substrate (operation 2600 ).
- a main lobe of a radiation pattern of the antenna is electronically steered in two dimensions (operation 2602 ), with the process terminating thereafter.
- FIG. 27 an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative embodiment.
- the process illustrated in Figure 27 may be implemented to electronically steer, for example, artificial impedance surface antenna 110 having switch elements as described in Figure 21 .
- the process begins by propagating a surface wave along each of a number of surface wave channels formed in each of a plurality of radiating elements to form a radiation pattern (operation 2700 ).
- each surface wave channel in the number of surface wave channels formed in each radiating element in the plurality of radiating elements may be coupled to a transmission line configured to carry a radio frequency signal using a surface wave feed in a plurality of surface wave feeds associated with the plurality of radiating elements (operation 2702 ).
- a main lobe of the radiation pattern may be electronically steered by controlling voltages applied to a plurality of switch elements connecting a plurality of impedance elements in each of the number of surface wave channels (operation 2704 ), with the process terminating thereafter.
- each block in the flowcharts or block diagrams may represent a module, a segment, a function, and/or a portion of an operation or step.
- the function or functions noted in the blocks may occur out of the order noted in the figures.
- two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved.
- other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.
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Description
- The present disclosure relates generally to antennas and, in particular, to electronically-steerable antennas. Still more particularly, the present disclosure relates to an electronically-steerable artificial impedance antenna capable of being steered in two dimensions.
- In various applications, having the capability to electronically steer an antenna in two directions may be desirable. As used herein, "steering" an antenna may include directing the primary gain lobe, or main lobe, of the radiation pattern of the antenna in a particular direction. Electronically steering an antenna means steering the antenna using electronic, rather than mechanical, means. Steering an antenna with respect to two dimensions may be referred to as two-dimensional steering.
- Currently, two-dimensional steering is typically provided by phased array antennas. However, currently available phased array antennas have electronic configurations that are more complex and/or more costly than desired. Consequently, having some other type of antenna that can be electronically steered in two dimensions and that is low-cost relative to a phased array antenna may be desirable.
- Artificial impedance surface antennas (AISAs) may be less expensive than phased array antennas. An artificial impedance surface antenna may be implemented by launching a surface wave across an artificial impedance surface (AIS) having an impedance that is spatially modulated across the artificial impedance surface according to a function that matches the phase fronts between the surface wave on the artificial impedance surface and the desired far-field radiation pattern. The basic principle of an artificial impedance surface antenna operation is to use the grid momentum of the modulated artificial impedance surface to match the wave vectors of an excited surface wave front to a desired plane wave.
- Some low-cost artificial impedance surface antennas may only be capable of being electronically steered in one dimension. In some cases, mechanical steering may be used to steer a one-dimensional artificial impedance surface antenna in a second dimension. However, mechanical steering may be undesirable in certain applications.
- A two-dimensional electronically-steerable artificial impedance surface antenna has been described in prior art. However, this type of antenna is more expensive and electronically complex than desired. For example, electronically steering this type of antenna in two dimensions may require a complex network of voltage control for a two-dimensional array of impedance elements. This network is used to create an arbitrary impedance pattern that can produce beam steering in any direction.
- In one illustrative example, a two-dimensional artificial impedance surface antenna may be implemented as a grid of metallic patches on a dielectric substrate. Each metallic path may be referred to as an impedance element. The surface wave impedance of the artificial impedance surface may be locally controlled at each position on the artificial impedance surface by applying a variable voltage to voltage-variable varactors connected between each of the patches. A varactor is a semiconductor element diode that has a capacitance dependent on the voltage applied to this diode.
- The surface wave impedance of the artificial impedance surface can be tuned with capacitive loads inserted between the patches. Each patch is electrically connected to neighboring patches on all four sides with voltage-variable varactor capacitors. The voltage is applied to the varactors through electrical vias connected to each patch. An electrical via may be an electrical connection that goes through the plane of one or more adjacent layers in an electronic circuit.
- One portion of the patches may be electrically connected to the ground plane with vias that run from the center of each patch down through the dielectric substrate. The rest of the patches may be electrically connected to voltage sources that run through the dielectric substrate, and through holes in the ground plane to the voltage sources.
- Computer control allows any desired impedance pattern to be applied to the artificial impedance surface within the limits of the varactor tunability and the limitations of the surface wave properties of the artificial impedance surface. One of the limitations of this method is that the vias can severely reduce the operational bandwidth of the artificial impedance surface because the vias also impart an inductance to the artificial impedance surface that shifts the surface wave bandgap to a lower frequency. As the varactors are tuned to higher capacitance, the artificial impedance surface inductance is increased, which may further reduce the surface wave bandgap frequency. The net result of the surface wave bandgap is that it does not allow the artificial impedance surface to be used above the bandgap frequency. Further, the surface wave bandgap also limits the range of surface wave impedance to that which the artificial impedance surface can be tuned.
- Consequently, an artificial impedance surface antenna that can be electronically steered in two dimensions and that is less expensive and less complex than some currently available two-dimensional artificial impedance surface antennas, such as the one described above, may be desirable in certain applications. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.
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US2014/0266946 , according to its abstract: Surface scattering antennas provide adjustable radiation fields by adjustably coupling scattering elements along a wave-propagating structure. In some approaches, the scattering elements are patch elements. In some approaches, the scattering elements are made adjustable by disposing an electrically adjustable material, such as a liquid crystal, in proximity to the scattering elements. Methods and systems provide control and adjustment of surface scattering antennas for various applications. -
EP2822096 , according to its abstract: An apparatus (100) comprising a plurality of radiating elements (122,123) and a plurality of surface wave feeds (130). Each radiating element in the plurality of radiating elements comprises a number of surface wave channels (125) in which each of the number of surface wave channels is configured to constrain a path of a surface wave. A surface wave feed in the plurality of surface wave feeds is configured to couple a surface wave channel in the number of surface wave channels of a radiating element in the plurality of radiating elements to a transmission line (156) configured to carry a radio frequency signal. - In one illustrative embodiment, an apparatus according to
clam 1 is provided. - According to an embodiment of the invention, an antenna system comprises a plurality of radiating elements and a plurality of surface wave feeds. Each of the plurality of radiating elements comprises a number of surface wave channels in which each of the number of surface wave channels is configured to constrain a path of a surface wave. Each of the number of surface wave channels comprises a plurality of impedance elements located on a surface of a dielectric substrate and a plurality of switch elements located on the surface of the dielectric substrate. Each of the plurality of switch elements has only two states. The plurality of surface wave feeds is configured to couple the number of surface wave channels of each of the plurality of radiating elements to a number of transmission lines.
- In another illustrative embodiment, a method according to claim 12 is provided.
- The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and features thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
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Figure 1 is an illustration of an antenna system in the form of a block diagram in accordance with an example useful for understanding the invention; -
Figure 2 is an illustration of an antenna system in accordance with an example useful for understanding of the invention; -
Figure 3 is an illustration of a side view of a portion of a tunable artificial impedance surface antenna in accordance with an example useful for understanding the invention; -
Figure 4 is an illustration of a different configuration for an antenna system in accordance with an example useful for understanding of the invention; -
Figure 5 is an illustration of another configuration for an antenna system in accordance with an example useful for understanding of the invention; -
Figure 6 is an illustration of a side view of a dielectric substrate in accordance with an
example useful for understanding the invention; -
Figure 7 is an illustration of a dielectric substrate having embedded pockets of material in accordance with an example useful for understanding the invention; -
Figure 8 is an illustration of an antenna system in accordance with an example useful for understanding of the invention; -
Figure 9 is another illustration of an antenna system in accordance with an example useful for understanding of the invention; -
Figure 10 is an illustration of an antenna system with a different voltage controller in accordance with an example useful for understanding of the invention; -
Figures 11A and11B are an illustration of yet another configuration for an antenna system in accordance with an example useful for understanding of the invention; -
Figure 12 is an illustration of a portion of an antenna system in accordance with an example useful for understanding of the invention; -
Figure 13 is an illustration of an antenna system having two radio frequency assemblies in accordance with example useful for understanding of the invention; -
Figure 14 is an illustration of another antenna system in accordance with an example useful for understanding of the invention; -
Figure 15 is an illustration of a different configuration for an artificial impedance surface antenna in an antenna system in the form of a block diagram in accordance with an example useful for understanding the invention; -
Figure 16 is an illustration of an artificial impedance surface antenna in accordance with an example useful for understanding of the invention; -
Figure 17 is an illustration of a cross-sectional side view of an artificial impedance surface antenna in accordance with an example useful for understanding the invention; -
Figure 18 is an illustration of an impedance pattern for an artificial impedance surface antenna in accordance with an example useful for understanding of the invention; -
Figure 19 is an illustration of a portion of an artificial impedance surface antenna in accordance with an example useful for understanding of the invention; -
Figure 20 is an illustration of a cross-sectional side view of an artificial impedance surface antenna in accordance with an example useful for understanding the invention; -
Figure 21 is an illustration of an artificial impedance surface antenna in the form of a block diagram in accordance with an illustrative embodiment; -
Figure 22 is an illustration of a radiating element in accordance with an illustrative embodiment; -
Figure 23 is an illustration of an enlarged view of a portion of a surface wave channel in accordance with an illustrative embodiment; -
Figure 24 is an illustration of a radiating element in accordance with an example useful for understanding the invention; -
Figure 25 is an illustration of a process for electronically steering an antenna system in the form of a flowchart in accordance with an example useful for understanding the invention; -
Figure 26 is an illustration of a process for electronically steering an antenna system in the form of a flowchart in accordance with an example useful for understanding the invention; and -
Figure 27 is an illustration of a process for electronically steering an antenna system in the form of a flowchart in accordance with an illustrative embodiment. - Referring now to the figures and, in particular, with reference to
Figure 1 , an illustration of an antenna system in the form of a block diagram is depicted in accordance with an example. -
Antenna system 100 may includeantenna 102,voltage controller 104,phase shifter 106, andradio frequency module 108.Antenna 102 takes the form of artificial impedance surface antenna (AISA) 110 in this illustrative example. -
Antenna 102 is configured to transmit and/or receiveradiation pattern 112.Radiation pattern 112 is a plot of the gain ofantenna 102 as a function of direction. The gain ofantenna 102 may be considered a performance parameter forantenna 102. In some cases, "gain" is considered the peak value of gain. -
Antenna 102 is configured to electronically controlradiation pattern 112. Whenantenna 102 is used for transmitting,radiation pattern 112 may be the strength of the radio waves transmitted fromantenna 102 as a function of direction.Radiation pattern 112 may be referred to as a transmitting pattern whenantenna 102 is used for transmitting. The gain ofantenna 102, when transmitting, may describe how wellantenna 102 converts electrical power into electromagnetic radiation, such as radio waves, and transmits the electromagnetic radiation in a specified direction. - When
antenna 102 is used for receiving,radiation pattern 112 may be the sensitivity ofantenna 102 to radio waves as a function of direction.Radiation pattern 112 may be referred to as a receiving pattern whenantenna 102 is used for receiving. The gain ofantenna 102, when used for receiving, may describe how wellantenna 102 converts electromagnetic radiation, such as radio waves, arriving from a specified direction into electrical power. - The transmitting pattern and receiving pattern of
antenna 102 may be identical. Consequently, the transmitting pattern and receiving pattern ofantenna 102 may be simply referred to asradiation pattern 112. -
Radiation pattern 112 may includemain lobe 116 and one or more side lobes.Main lobe 116 may be the lobe at the direction in whichantenna 102 is being directed. Whenantenna 102 is used for transmitting,main lobe 116 is located at the direction in whichantenna 102 transmits the strongest radio waves to form a radio frequency beam. Whenantenna 102 is used for transmitting,main lobe 116 may also be referred to as the primary gain lobe ofradiation pattern 112. Whenantenna 102 is used for receiving,main lobe 116 is located at the direction in whichantenna 102 is most sensitive to incoming radio waves. - In this illustrative example,
antenna 102 is configured to electronically steermain lobe 116 ofradiation pattern 112 in desireddirection 114.Main lobe 116 ofradiation pattern 112 may be electronically steered by controllingphi steering angle 118 andtheta steering angle 120 at whichmain lobe 116 is directed.Phi steering angle 118 andtheta steering angle 120 are spherical coordinates. Whenantenna 102 is operating in an X-Y plane,phi steering angle 118 is the angle ofmain lobe 116 in the X-Y plane relative to the X-axis. Further,theta steering angle 120 is the angle ofmain lobe 116 relative to a Z-axis that is orthogonal to the X-Y plane. -
Antenna 102 may operate in the X-Y plane by having array of radiatingelements 122 that lie in the X-Y plane. As used herein, an "array" of items may include one or more items arranged in rows and/or columns. In this illustrative example, array of radiatingelements 122 may be a single radiating element or a plurality of radiating elements. In one illustrative example, each radiating element in array of radiatingelements 122 may take the form of an artificial impedance surface, surface wave waveguide structure. -
Radiating element 123 may be an example of one radiating element in array of radiatingelements 122.Radiating element 123 may be configured to emit radiation that contributes toradiation pattern 112. - As depicted, radiating
element 123 is implemented usingdielectric substrate 124.Dielectric substrate 124 may be implemented as a layer of dielectric material. A dielectric material is an electrical insulator that can be polarized by an applied electric field. -
Radiating element 123 may include one or more surface wave channels that are formed ondielectric substrate 124. For example, radiatingelement 123 may includesurface wave channel 125.Surface wave channel 125 is configured to constrain the path of surface waves propagated alongdielectric substrate 124, andsurface wave channel 125 in particular. - In one illustrative example, array of radiating
elements 122 may be positioned substantially parallel to the X-axis and arranged and spaced along the Y-axis. Further, when more than one surface wave channel is formed on a dielectric substrate, these surface wave channels may be formed substantially parallel to the X-axis and arranged and spaced along the Y-axis. - In this illustrative example, impedance elements and tunable elements located on a dielectric substrate may be used to form each surface wave channel of a radiating element in array of radiating
elements 122. For example,surface wave channel 125 may be comprised of plurality ofimpedance elements 126 and plurality oftunable elements 128 located on the surface ofdielectric substrate 124. Together, plurality ofimpedance elements 126, plurality oftunable elements 128, anddielectric substrate 124 form an artificial impedance surface from which radiation is generated. - An impedance element in plurality of
impedance elements 126 may be implemented in a number of different ways. In one illustrative example, an impedance element may be implemented as a resonating element. In one illustrative example, an impedance element may be implemented as an element comprised of a conductive material. The conductive material may be, for example, without limitation, a metallic material. Depending on the implementation, an impedance element may be implemented as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate, or some other type of conductive element. In some cases, an impedance element may be implemented as a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element. - As used herein, a metamaterial may be an artificial material engineered to have properties that may not be found in nature. A metamaterial may be an assembly of multiple individual elements formed from conventional microscopic materials. These conventional materials may include, for example, without limitation, metal, a metal alloy, a plastic material, and other types of materials. However, these conventional materials may be arranged in repeating patterns. The properties of a metamaterial may be based, not on the composition of the metamaterial, but on the exactingly-designed structure of the metamaterial. In particular, the precise shape, geometry, size, orientation, arrangement, or combination thereof may be exactly designed to produce a metamaterial with specific properties that may not be found or readily found in nature.
- Each one of plurality of
tunable elements 128 may be an element that can be controlled, or tuned, to change an angle of the one or more surface waves being propagated along radiatingelement 123. In this illustrative example, each of plurality oftunable elements 128 may be an element having a capacitance that can be varied based on the voltage applied to the tunable element. - In one illustrative example, plurality of
impedance elements 126 takes the form of plurality ofmetallic strips 132 and plurality oftunable elements 128 takes the form of plurality ofvaractors 134. Each of plurality ofvaractors 134 may be a semiconductor element diode that has a capacitance dependent on the voltage applied to the semiconductor element diode. - In one illustrative example, plurality of
metallic strips 132 may be arranged in a row that extends along the X-axis. For example, plurality ofmetallic strips 132 may be periodically distributed ondielectric substrate 124 along the X-axis. Plurality ofvaractors 134 may be electrically connected to plurality ofmetallic strips 132 on the surface ofdielectric substrate 124. In particular, at least one varactor in plurality ofvaractors 134 may be positioned between each adjacent pair of metallic strips in plurality ofmetallic strips 132. Further, plurality ofvaractors 134 may be aligned such that all of the varactor connections on each metallic strip have the same polarity. -
Dielectric substrate 124, plurality ofimpedance elements 126, and plurality oftunable elements 128 may be configured with respect to selecteddesign configuration 136 forsurface wave channel 125, and radiatingelement 123 in particular. Depending on the implementation, each radiating element in array of radiatingelements 122 may have a same or different selected design configuration. - As depicted, selected
design configuration 136 may include a number of design parameters such as, but not limited to,impedance element width 138, impedance element spacing 140, tunable element spacing 142, andsubstrate thickness 144.Impedance element width 138 may be the width of an impedance element in plurality ofimpedance elements 126.Impedance element width 138 may be selected to be the same or different for each of plurality ofimpedance elements 126, depending on the implementation. - Impedance element spacing 140 may be the spacing of plurality of
impedance elements 126 with respect to the X-axis. Tunable element spacing 142 may be the spacing of plurality oftunable elements 128 with respect to the X-axis. Further,substrate thickness 144 may be the thickness ofdielectric substrate 124 on which a particular waveguide is implemented. - The values for the different parameters in selected
design configuration 136 may be selected based on, for example, without limitation, the radiation frequency at whichantenna 102 is configured to operate. Other considerations include, for example, the desired impedance modulations forantenna 102. - Voltages may be applied to plurality of
tunable elements 128 by applying voltages to plurality ofimpedance elements 126 because plurality ofimpedance elements 126 may be electrically connected to plurality oftunable elements 128. In particular, the voltages applied to plurality ofimpedance elements 126, and thereby plurality oftunable elements 128, may change the capacitance of plurality oftunable elements 128. Changing the capacitance of plurality oftunable elements 128 may, in turn, change the surface impedance ofantenna 102. Changing the surface impedance ofantenna 102 changesradiation pattern 112 produced. - In other words, by controlling the voltages applied to plurality of
impedance elements 126, the capacitances of plurality oftunable elements 128 may be varied. Varying the capacitances of plurality oftunable elements 128 may vary, or modulate, the capacitive coupling and impedance between plurality ofimpedance elements 126. Varying, or modulating, the capacitive coupling and impedance between plurality ofimpedance elements 126 may changetheta steering angle 120. - The voltages may be applied to plurality of
impedance elements 126 usingvoltage controller 104.Voltage controller 104 may include number ofvoltage sources 146, number ofgrounds 148, number ofvoltage lines 150, and/or some other type of component. In some cases,voltage controller 104 may be referred to as a voltage control network. As used herein, a "number of" items may include one or more items. For example, number ofvoltage sources 146 may include one or more voltage sources; number ofgrounds 148 may include one or more grounds; and number ofvoltage lines 150 may include one or more voltage lines. - A voltage source in number of
voltage sources 146 may take the form of, for example, without limitation, a digital to analog converter (DAC), a variable voltage source, or some other type of voltage source. Number ofgrounds 148 may be used to ground at least a portion of plurality ofimpedance elements 126. Number ofvoltage lines 150 may be used to transmit voltage from number ofvoltage sources 146 and/or number ofgrounds 148 to plurality ofimpedance elements 126. In some cases, each of number ofvoltage lines 150 may be referred to as a via. In one illustrative example, number ofvoltage lines 150 may take the form of a number of metallic vias. - In one illustrative example, each of plurality of
impedance elements 126 may receive voltage from one of number ofvoltage sources 146. In another illustrative example, a portion of plurality ofimpedance elements 126 may receive voltage from number ofvoltage sources 146 through a corresponding portion of number ofvoltage lines 150, while another portion of plurality ofimpedance elements 126 may be electrically connected to number ofgrounds 148 through a corresponding portion of number ofvoltage lines 150. - In some cases,
controller 151 may be used to control number ofvoltage sources 146.Controller 151 may be considered part of or separate fromantenna system 100, depending on the implementation.Controller 151 may be implemented using a microprocessor, an integrated circuit, a computer, a central processing unit, a plurality of computers in communication with each other, or some other type of computer or processor. - Surface waves 152 propagated along array of radiating
elements 122 may be coupled to number oftransmission lines 156 by plurality of surface wave feeds 130 located ondielectric substrate 124. A surface wave feed in plurality of surface wave feeds 130 may be any device that is capable of converting a surface wave into a radio frequency signal and/or a radio frequency signal into a surface wave. In one illustrative example, a surface wave feed in plurality of surface wave feeds 130 is located at the end of each waveguide in array of radiatingelements 122 ondielectric substrate 124. - For example, when
antenna 102 is in a receiving mode, the one or more surface waves propagating along radiatingelement 123 may be received at a corresponding surface wave feed in plurality of surface wave feeds 130 and converted into a correspondingradio frequency signal 154.Radio frequency signal 154 may be sent toradio frequency module 108 over one or more of number oftransmission lines 156.Radio frequency module 108 may then function as a receiver and processradio frequency signal 154 accordingly. - Depending on the implementation,
radio frequency module 108 may function as a transmitter, a receiver, or a combination of the two. In some illustrative examples,radio frequency module 108 may be referred to as transmit/receivemodule 158. In some cases, when configured for transmitting,radio frequency module 108 may be referred to as a radio frequency source. - In some cases,
radio frequency signal 154 may pass throughphase shifter 106 prior to being sent toradio frequency module 108.Phase shifter 106 may include any number of phase shifters, power dividers, transmission lines, and/or other components configured to shift the phase ofradio frequency signal 154. In some cases,phase shifter 106 may be referred to as a phase-shifting network. - When
antenna 102 is in a transmitting mode,radio frequency signal 154 may be sent fromradio frequency module 108 toantenna 102 over number oftransmission lines 156. In particular,radio frequency signal 154 may be received at one of plurality of surface wave feeds 130 and converted into one or more surface waves that are then propagated along a corresponding waveguide in array of radiatingelements 122. - In this illustrative example, the relative phase difference between plurality of surface wave feeds 130 may be changed to change
phi steering angle 118 ofradiation pattern 112 that is transmitted or received. Thus, by controlling the relative phase difference between plurality of surface wave feeds 130 and controlling the voltages applied to the tunable elements of each waveguide in array of radiatingelements 122,phi steering angle 118 andtheta steering angle 120, respectively, may be controlled. In other words,antenna 102 may be electronically steered in two dimensions. - Depending on the implementation, radiating
element 123 may be configured to emit linearly polarized radiation or circularly polarized radiation. When configured to emit linearly polarized radiation, the plurality of metallic strips used for each surface wave channel on radiatingelement 123 may be angled in the same direction relative to the X-axis along which the plurality of metallic strips are distributed. Typically, only a single surface wave channel is needed for each radiatingelement 123. - However, when radiating
element 123 is configured for producing circularly polarized radiation,surface wave channel 125 may be a first surface wave channel and secondsurface wave channel 145 may be also present in radiatingelement 123.Surface wave channel 125 and secondsurface wave channel 145 may be about 90 degrees out of phase from each other. The interaction between the radiation from these two coupled surface wave channels makes it possible to create circularly polarized radiation. - Plurality of
impedance elements 126 that formsurface wave channel 125 may be a first plurality of impedance elements that radiate with a polarization at an angle to the polarization of the surface wave electric field. A second plurality of impedance elements that form secondsurface wave channel 145 may radiate with a polarization at an angle offset about 90 degrees as compared tosurface wave channel 125. - For example, each impedance element in the first plurality of impedance elements of
surface wave channel 125 may have a tensor impedance with a principal angle that is angled at a first angle relative to an X-axis of radiatingelement 123. Further, each impedance element in the second plurality of impedance elements of secondsurface wave channel 145 may have a tensor impedance that is angled at a second angle relative to the X-axis of the corresponding radiating element. The difference between the first angle and the second angle may be about 90 degrees. - The capacitance between the first plurality of impedance elements may be controlled using plurality of
tunable elements 128, which may be a first plurality of tunable elements. The capacitance between the second plurality of impedance elements may be controlled using a second plurality of tunable elements. - As a more specific example, plurality of
metallic strips 132 onsurface wave channel 125 may be angled at about positive 45 degrees with respect to the X-axis along which plurality ofmetallic strips 132 is distributed. However, the plurality of metallic strips used for secondsurface wave channel 145 may be angled at about negative 45 degrees with respect to the X-axis along which the plurality of metallic strips is distributed. This variation in tilt angle produces radiation of different linear polarizations, that when combined with a 90 degree phase shift, may produce circularly polarized radiation. - The illustration of
antenna system 100 inFigure 1 is not meant to imply physical or architectural limitations to the manner in which an example may be implemented. Other components in addition to or in place of the ones illustrated may be used. Some components may be optional. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative example. - For example, in other illustrative examples,
phase shifter 106 may not be included inantenna system 100. Instead, number oftransmission lines 156 may be used to couple plurality of surface wave feeds 130 to a number of power dividers and/or other types of components, and these different components toradio frequency module 108. In some examples, number oftransmission lines 156 may directly couple plurality of surface wave feeds 130 toradio frequency module 108. - In some illustrative examples, a tunable element in plurality of
tunable elements 128 may be implemented as a pocket of variable material embedded indielectric substrate 124. As used herein, a "variable material" may be any material having a permittivity that may be varied. The permittivity of the variable material may be varied to change, for example, the capacitance between two impedance elements between which the variable material is located. The variable material may be a voltage-variable material or any electrically variable material, such as, for example, without limitation, a liquid crystal material or barium strontium titanate (BST). - In other illustrative examples, a tunable element in plurality of
tunable elements 128 may be part of a corresponding impedance element in plurality ofimpedance elements 126. For example, a resonant structure having a tunable element may be used. The resonant structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled resonator, or some other type of resonant structure. - With reference now to
Figure 2 , an illustration of an antenna system is depicted in accordance with an example. -
Antenna system 200 may be an example of one implementation forantenna system 100 inFigure 1 . As depicted,antenna system 200 includes tunable artificial impedance surface antenna (AISA) 201, which may be an example of one implementation for artificialimpedance surface antenna 110 inFigure 1 . Further,antenna system 200 may also includevoltage controller 202 andphase shifter 203.Voltage controller 202 andphase shifter 203 may be examples of implementations forvoltage controller 104 andphase shifter 106, respectively, inFigure 1 . - In this illustrative example, tunable artificial
impedance surface antenna 201 is a relatively low cost antenna capable of being electronically steered in both theta, θ, and phi, φ, directions. When tunable artificialimpedance surface antenna 201 is operating in the X-Y plane, the theta direction may be a direction perpendicular to the Z axis that is perpendicular to the X-Y plane, while the phi direction may be a direction parallel to the X-Y plane. - As depicted, tunable artificial
impedance surface antenna 201 includesdielectric substrate 206,metallic strips 207,varactors 209, and radio frequency (RF) surface wave feeds 208.Metallic strips 207 may be a periodic array ofmetallic strips 207 that are located on one surface ofdielectric substrate 206.Varactors 209 may be located betweenmetallic strips 207.Dielectric substrate 206 may or may not have a ground plane (not shown in this view) on a surface ofdielectric substrate 206 opposite to the surface on whichmetallic strips 207 are located. - Steering of the main lobe of tunable artificial
impedance surface antenna 201 in the theta direction is controlled by varying, or modulating, the surface wave impedance of tunable artificialimpedance surface antenna 201. For example, the impedance of tunable artificialimpedance surface antenna 201 may be varied, or modulated, by controlling the voltages applied tometallic strips 207 located on the surface ofdielectric substrate 206. Withvaractors 209 present betweenmetallic strips 207, the voltage applied tovaractors 209 may be controlled usingmetallic strips 207. Each ofvaractors 209 is a type of diode that has a capacitance that varies as a function of the voltage applied across the terminals of the diode. - The voltages applied to
metallic strips 207 may change the capacitance ofvaractors 209 betweenmetallic strips 207, which may, in turn, change the impedance of tunable artificialimpedance surface antenna 201. In other words, by controlling the voltages applied tometallic strips 207, the capacitances ofvaractors 209 may be varied. Varying the capacitances ofvaractors 209 may vary or modulate the capacitive coupling and impedance betweenmetallic strips 207 to steer the beam produced byantenna system 200 in the theta direction. - In this illustrative example, radio frequency surface wave feeds 208 may be a two-dimensional array of radio frequency surface wave feeds. Steering of the main lobe of tunable artificial
impedance surface antenna 201 in the phi direction is controlled by changing the relative phase difference between radio frequency surface wave feeds 208. -
Voltage controller 202 is used to apply direct current (DC) voltages tometallic strips 207 on the structure of tunable artificialimpedance surface antenna 201.Voltage controller 202 may be controlled based on commands received throughcontrol bus 205. In this manner,control bus 205 provides control forvoltage controller 202. Further,control bus 204 may provide control forphase shifter 203. Each ofcontrol bus 204 andcontrol bus 205 may be a bus from a microprocessor, a central processing unit (CPU), one or more computers, or some other type of computer or processor. - In this illustrative example, the polarities of
varactors 209 may be aligned such that all varactor connections to any one ofmetallic strips 207 may be connected with the same polarity. One terminal on a varactor may be referred to as an anode, and the other terminal may be referred to as a cathode. Thus, some ofmetallic strips 207 are only connected to anodes ofvaractors 209, while other ofmetallic strips 207 are only connected to cathodes ofvaractors 209. Further, as depicted, adjacentmetallic strips 207 may alternate with respect to which ones are connected to the anodes ofvaractors 209 and which ones are connected to the cathodes ofvaractors 209. - The spacing of
metallic strips 207 in one dimension of tunable artificialimpedance surface antenna 201, which may be in an X direction, may be a fraction of the radio frequency surface wave wavelength of the radio frequency waves that propagate across tunable artificialimpedance surface antenna 201 from radio frequency surface wave feeds 208. In one illustrative example, the spacing ofmetallic strips 207 may be at most 2/5 of the radio frequency surface wave wavelength of the radio frequency waves. In another illustrative example, the fraction may be only about 2/10 of the radio frequency surface wave wavelength of the radio frequency waves. Depending on the implementation, the spacing betweenvaractors 209 connected tometallic strips 207 in a second dimension of tunable artificialimpedance surface antenna 201, which may be in a Y direction, may be about the same as the spacing betweenmetallic strips 207. - Radio frequency surface wave feeds 208 may form a phased array corporate feed structure, or may take the form of conformal surface wave feeds, which are integrated into tunable artificial
impedance surface antenna 201. The surface wave feeds may be integrated into tunable artificialimpedance surface antenna 201, for example, using microstrips. The spacing between radio frequency surface wave feeds 208 in the Y direction may be based on selected rules that indicate that the spacing be no farther apart than the free-space wavelength for the highest frequency signal to be transmitted or received. - In this illustrative example, the thickness of
dielectric substrate 206 may be determined by the permittivity ofdielectric substrate 206 and the frequency of radiation to be transmitted or received. The higher the permittivity, the thinnerdielectric substrate 206 may be. - The capacitance values of
varactors 209 may be determined by the range needed for the desired impedance modulations for tunable artificialimpedance surface antenna 201 in order to obtain the various angles of radiation. Further, the particular substrate used fordielectric substrate 206 may be selected based on the operating frequency, or radio frequency, of tunable artificialimpedance surface antenna 201. - For example, when tunable artificial
impedance surface antenna 201 is operating at about 20 gigahertz,dielectric substrate 206 may be implemented using, without limitation, a substrate, available from Rogers Corporation, having a thickness of about 50 millimeters (mm). In this example,dielectric substrate 206 may have a relative permittivity equal to about 12.2.Metallic strips 207 may be spaced about two millimeters to about three millimeters apart ondielectric substrate 206. Further, radio frequency surface wave feeds 208 may be spaced about 2.5 centimeters apart andvaractors 209 may be spaced about two millimeters to about three millimeters apart in this example.Varactors 209 may vary in capacitance from about 0.2 picofarads (pF) to about 2.0 picofarads. Of course, other specifications may be used for tunable artificialimpedance surface antenna 201 for different radiation frequencies. - To transmit or receive a radio frequency signal using tunable artificial
impedance surface antenna 201, transmit/receivemodule 210 is connected to phaseshifter 203.Phase shifter 203 may be a one-dimensional phase shifter in this illustrative example.Phase shifter 203 may be implemented using any type of currently available phase shifter, including those used in phased array antennas. - In this illustrative example,
phase shifter 203 includes radiofrequency transmission lines 211 connected to transmit/receivemodule 210,power dividers 212, andphase shifters 213.Phase shifters 213 are controlled byvoltage control lines 216 connected to digital to analog converter (DAC) 214. Digital toanalog converter 214 receives digital control signals fromcontrol bus 204 to control the steering in the phi direction. - The main lobe of tunable artificial
impedance surface antenna 201 may be steered in the phi direction by usingphase shifter 203 to impose a phase shift between each of radio frequency surface wave feeds 208. If radio frequency surface wave feeds 208 are spaced uniformly, then the phase shift between adjacent radio frequency surface wave feeds 208 may be substantially constant. The relationship between the phi (φ) steering angle and the phase shift may be calculated using standard phased array methods, according to the following equation: - As described earlier, the main lobe of tunable artificial
impedance surface antenna 201 may be steered in the theta (θ) direction by applying voltages tovaractors 209 such that tunable artificialimpedance surface antenna 201 has surface wave impedance Zsw, which is modulated or varied periodically with the distance (x) away from radio frequency surface wave feeds 208, according to the following equation:impedance surface antenna 201, and p is the modulation period. The variation of the surface wave impedance, Zsw, may be modulated sinusoidally. The theta steering angle, θ, is related to the impedance modulation by the following equation: - The beam is steered in the theta direction by tuning the voltages applied to
varactors 209 such that X, M, and p result in the desired theta steering angle, θ. The dependence of the surface wave impedance on the varactor capacitance is calculated using transcendental equations resulting from the transverse resonance method or by using full-wave numerical simulations. - Voltages may be applied to
varactors 209 by grounding alternatemetallic strips 207 toground 220 viavoltage control lines 218 and applying tunable voltages viavoltage control lines 219 to the rest ofmetallic strips 207. The voltage applied to each ofvoltage control lines 219 may be a function of the desired theta steering angle and may be different for each of voltage control lines 219. The voltages may be applied from digital-to-analog converter (DAC) 217 that receives digital controls fromcontrol bus 205 from a controller for steering in the theta direction. The controller may be a microprocessor, central processing unit (CPU) or any computer, processor or controller. - One benefit of grounding half of
metallic strips 207 is that only half as manyvoltage control lines 219 are required as there aremetallic strips 207. However, in some cases, the spatial resolution of the voltage control and hence, the impedance modulation, may be limited to twice the spacing betweenmetallic strips 207. - With reference now to
Figure 3 , an illustration of a side view of a portion of tunable artificialimpedance surface antenna 201 fromFigure 2 is depicted in accordance with an example. - In this illustrative example,
dielectric substrate 206 hasground plane 300. - With reference now to
Figure 4 , an illustration of a different configuration for an antenna system is depicted in accordance with an illustrative example. -
Antenna system 400 may be an example of one implementation forantenna system 100 inFigure 1 .Antenna system 400 includes tunable artificial impedance surface antenna (AISA) 401, which may be an example of one implementation for artificialimpedance surface antenna 110 inFigure 1 . -
Antenna system 400 and tunable artificialimpedance surface antenna 401 may be implemented in a manner similar toantenna system 200 and tunable artificialimpedance surface antenna 201, respectively, fromFigure 2 . As depicted,antenna system 400 includes tunable artificialimpedance surface antenna 401,voltage controller 402, andphase shifter 403. Tunable artificialimpedance surface antenna 401 includesdielectric substrate 406,metallic strips 407,varactors 409, and radio frequency surface wave feeds 408. Further,antenna system 400 may include transmit/receivemodule 410. - However, in this illustrative example,
voltage controller 402 may be implemented in a manner different from the manner in whichvoltage controller 202 is implemented inFigure 2 . InFigure 4 ,voltage controller 402 may includevoltage lines 411 that allow voltage to be applied from digital toanalog converter 412 to each ofmetallic strips 407. Alternatingmetallic strips 407 are not grounded as inFigure 2 . Digital toanalog converter 412 may receive digital controls fromcontrol bus 205 inFigure 2 from, for example,controller 414, for steering in the theta direction.Controller 414 may be implemented using a microprocessor, a central processing unit, or some other type of computer or processor. Steering in the phi direction may be performed usingphase shifter 403 in a manner similar to the manner in whichphase shifter 203 is used inFigure 2 . - With
voltage lines 411 applying voltage to all ofmetallic strips 407, twice as many control voltages are required compared toantenna system 200 inFigure 2 . However, the spatial resolution of the impedance modulation of tunable artificialimpedance surface antenna 401 is doubled. In this illustrative example, the voltage applied to each ofvoltage lines 411 is a function of the desired theta steering angle, and may be different for each ofvoltage lines 411. - With reference now to
Figure 5 , an illustration of another configuration for an antenna system is depicted in accordance with an example. -
Antenna system 500 may be an example of one implementation forantenna system 100 inFigure 1 .Antenna system 500 includes tunable artificial impedance surface antenna (AISA) 501, which may be an example of one implementation for artificialimpedance surface antenna 110 inFigure 1 . -
Antenna system 500 and tunable artificialimpedance surface antenna 501 may be implemented in a manner similar toantenna system 200 and tunable artificialimpedance surface antenna 201, respectively, fromFigure 2 . Further,antenna system 500 and tunable artificialimpedance surface antenna 501 may be implemented in a manner similar toantenna system 400 and tunable artificialimpedance surface antenna 401, respectively, fromFigure 4 . - As depicted,
antenna system 500 includes tunable artificialimpedance surface antenna 501,voltage controller 502, andphase shifter 503. Tunable artificialimpedance surface antenna 501 includesdielectric substrate 506,metallic strips 507,varactors 509, and radio frequency surface wave feeds 508. Further,antenna system 500 may include transmit/receivemodule 510. - However, in this illustrative example,
voltage controller 502 may be implemented in a manner different from the manner in whichvoltage controller 202 is implemented inFigure 2 and in a manner different from the manner in whichvoltage controller 402 is implemented inFigure 4 . InFigure 5 , the digital to analog converters ofFigure 2 andFigure 4 have been replaced byvariable voltage source 512. - As the voltage of
variable voltage source 512 is varied, the radiation angle of the beam produced by tunable artificialimpedance surface antenna 501 varies between a minimum theta steering angle and a maximum theta steering angle. This range for the theta steering angle may be determined by the details of the design configuration of tunable artificialimpedance surface antenna 501. - The voltage is applied to
metallic strips 507 throughvoltage control lines 514 and voltage control lines 516.Voltage control lines 516 may provide a ground formetallic strips 507, whilevoltage control lines 514 may providemetallic strips 507 with a variable voltage. Across the X dimension,metallic strips 507 are alternately connected tovoltage control lines 514 or voltage control lines 516. In other words, alternatingmetallic strips 507 are grounded. -
Metallic strips 507 may have centers that are equally spaced in the X dimension, with the widths ofmetallic strips 507 periodically varying with a period (p) 518. The number ofmetallic strips 507 inperiod 518 may be any number. For example,metallic strips 507 may be between 10 and 20 metallic strips perperiod 518. The width variation perperiod 518 may be configured to produce surface wave impedance with a periodic modulation in the X-direction withperiod 518, such as, for example, the sinusoidal variation of equation (3) described above. - The surface wave impedance at each point on tunable artificial
impedance surface antenna 501 is determined by the width of each ofmetallic strips 507 and the voltage applied tovaractors 509. The capacitance ofvaractors 509 may vary with the varying applied voltage. When the voltage is about 0 volts, the capacitance of a varactor may be at a maximum value of Cmax. The capacitance decreases as the voltage is increased until the capacitance reaches a minimum value of Cmin . As the capacitance is varied, the impedance modulation parameters, X and M, as described inequation 2 above, may also vary from minimum values of Xmin and Mmin, respectively, to maximum values of Xmax and Mmax, respectively. - Further, the mean surface wave index of equation 4 described above varies from
equation 3 above, the range that the radiation angle of tunable artificialimpedance surface antenna 501 may be scanned may vary from a minimum of - With reference now to
Figure 6 , an illustration of a side view of a dielectric substrate is depicted in accordance with an example. In this illustrative example,dielectric substrate 601 may be used to implementdielectric substrate 206 fromFigure 2 ,dielectric substrate 406 fromFigure 4 , and/ordielectric substrate 506 fromFigure 5 .Dielectric substrate 601 may have an electrical permittivity that is varied with the application of an electric field. -
Metallic strips 602 are shown located on one surface ofdielectric substrate 601. As depicted, no varactors are used in this illustrative example. When a voltage is applied tometallic strips 602, an electric field is produced between adjacentmetallic strips 602 and also betweenmetallic strips 602 andground plane 603. The electric field changes the permittivity ofdielectric substrate 601, which results in a change in the capacitance between adjacentmetallic strips 602. The capacitance between adjacentmetallic strips 602 determines the surface wave impedance of the tunable artificial impedance surface antenna that usesdielectric substrate 601. - With reference now to
Figure 7 , an illustration ofdielectric substrate 601 fromFigure 6 having embedded pockets of material is depicted in accordance with an illustrative example. - In this illustrative example,
dielectric substrate 601 may take the form ofinert substrate 700. A voltage differential may be applied to adjacentmetallic strips 602, which may create an electric field betweenmetallic strips 602 and produce a permittivity change in pockets ofvariable material 702 located betweenmetallic strips 602. - Pockets of
variable material 702 may be an example of one manner in which plurality oftunable elements 128 inFigure 1 may be implemented. The variable material in pockets ofvariable material 702 may be any electrically variable material, such as, for example, without limitation, a liquid crystal material or barium strontium titanate (BST). In particular,variable material 702 is embedded in pockets withindielectric substrate 601 betweenmetallic strips 602. - With reference now to
Figure 8 , an illustration of an antenna system is depicted in accordance with an example. - In this illustrative example,
antenna system 800 may be an example of one implementation forantenna system 100 inFigure 1 .Antenna system 800 includesantenna 802,voltage controller 803,phase shifter 804, andradio frequency module 806.Antenna 802,voltage controller 803,phase shifter 804, andradio frequency module 806 may be examples of implementations forantenna 102,voltage controller 104,phase shifter 106, andradio frequency module 108, respectively, inFigure 1 . -
Antenna 802 is supplied voltage byvoltage controller 803.Voltage controller 803 includes digital to analog converter (DAC) 808 andvoltage lines 811. Digital toanalog converter 808 may be an example of one implementation for a voltage source in number ofvoltage sources 146 inFigure 1 .Voltage lines 811 may be an example of one implementation for number ofvoltage lines 150 inFigure 1 . - Voltage may be applied to
antenna 802 from digital toanalog converter 808 throughvoltage lines 811.Controller 810 may be used to control the voltage signals sent from digital toanalog converter 808 toantenna 802.Controller 810 may be an example of one implementation forcontroller 151 inFigure 1 . In this illustrative example,controller 810 may be considered part ofantenna system 800. - As depicted,
antenna 802 may include radiatingstructure 812 formed by array of radiatingelements 813. Array of radiatingelements 813 may be an example of one implementation for array of radiatingelements 122 inFigure 1 . In this illustrative example, each radiating element in array of radiatingelements 813 may be implemented as an artificial impedance surface, surface wave waveguide. - Array of radiating
elements 813 may include radiatingelements - As one illustrative example, radiating
element 814 may be formed bydielectric substrate 827. Plurality ofmetallic strips 828 and plurality ofvaractors 830 may be located on the surface ofdielectric substrate 827 to formsurface wave channel 831. Further, surface wave feed 832 may be located on the surface ofdielectric substrate 827. Plurality ofmetallic strips 828 and plurality ofvaractors 830 may be examples of implementations for plurality ofmetallic strips 132 and plurality ofvaractors 134, respectively, inFigure 1 . - In the transmitting mode, surface wave feed 832 feeds a surface wave into
surface wave channel 831 of radiatingelement 814.Surface wave channel 831 confines the surface wave to propagate linearly along a confined path across plurality ofmetallic strips 828. In particular,surface wave channel 831 creates a region of high surface wave index surrounded by a region of lower surface wave index to confine the surface wave to the set path. The surface wave index is the ratio between the speed of light and the propagation speed of the surface wave. - The regions of high surface wave index are created by plurality of
metallic strips 828 and plurality ofvaractors 830, while the regions of low surface wave index are created by the bare surface ofdielectric substrate 827. The widths of the regions of high surface wave index may be 50 percent to about 100 percent times the length of the surface wave wavelength. The surface wave wavelength is as follows: - Each of plurality of
metallic strips 828 located ondielectric substrate 827 may have the same width. Further, these metallic strips may be equally spaced alongdielectric substrate 827. Additionally, plurality ofvaractors 830 may also be equally spaced alongdielectric substrate 827. In other words, plurality ofmetallic strips 828 and plurality ofvaractors 830 may be periodically distributed ondielectric substrate 827. Further, plurality ofvaractors 830 may be aligned such that all of the varactors connections of plurality ofmetallic strips 828 have the same polarity. - The thickness of
dielectric substrate 827 may be determined by its permittivity and the frequency of radiation to be transmitted or received. The higher the permittivity, the thinnerdielectric substrate 827 may be. - The capacitance values of plurality of
varactors 830 may be determined by the range needed for the desired impedance modulations for the various angles of radiation. The main lobe of the radiation pattern produced byantenna 802 may be electronically steered in the theta direction by applying voltages to the various varactors in array of radiatingelements 813. Voltage may be applied to these varactors such thatantenna 802 has a surface wave impedance that varies sinusoidally with a distance, x, away from the surface wave feeds on the different dielectric substrates. - Voltage from digital to
analog converter 808 may be applied to the metallic strips on array of radiatingelements 813 throughvoltage lines 811. In this illustrative example, surface waves propagated across array of radiatingelements 813 may be coupled tophase shifter 804 by the surface wave feeds on array of radiatingelements 813.Phase shifter 804 includes plurality of phase-shiftingdevices 834. - The main lobe of
antenna 802 may be electronically steered in the phi direction by imposing a phase shift between each of the surface wave feeds on array of radiatingelements 813. If the surface wave feeds are uniformly spaced, the phase shift between adjacent surface wave feeds may be substantially constant. The relation between the phi steering angle and this phase shift may be calculated as follows: - In other illustrative examples, a radio frequency module, a phase shifter, and a plurality of surface wave feeds may be present on the opposite side of
antenna 802 relative toradio frequency module 806. This configuration may be used in order to facilitate steering in the negative theta direction. - With reference now to
Figure 9 , another illustration of an antenna system is depicted in accordance with an example. - In this illustrative example,
antenna system 900 may be an example of one implementation forantenna system 100 inFigure 1 .Antenna system 900 includesantenna 902,voltage controller 903,phase shifter 904, andradio frequency module 906. -
Voltage controller 903 is configured to supply voltage toantenna 902.Voltage controller 903 includesvariable voltage source 908.Voltage lines 911 apply voltage toantenna 902, whilevoltage lines 913 provide ground forantenna 902. -
Antenna 902 may include array of radiatingelements 915 that may include radiatingelements - For example, radiating
element 912 may be formed usingdielectric substrate 927. First plurality ofmetallic strips 928, second plurality ofmetallic strips 930, and plurality ofvaractors 932 located on the surface ofdielectric substrate 927 may formsurface wave channel 931. Surface wave feed 933 is also located on the surface ofdielectric substrate 927 and couples a surface wave propagated alongsurface wave channel 931 tophase shifter 904. - Each of first plurality of
metallic strips 928 located on array of radiatingelements 915 may have the same width. Further, each of second plurality ofmetallic strips 930 located on array of radiatingelements 915 may have the same width. The width of the metallic strips in both first plurality ofmetallic strips 928 and second plurality ofmetallic strips 930 varies periodically alongdielectric substrate 927 with period, p, 934. This period may be determined by the size of the metallic strips, the radiation frequency, the theta steering angle, and the properties and thickness ofdielectric substrate 927. - Although only two widths for the metallic strips are shown within one period, any number of metallic strips may be included within a period. Further, any number of different widths may be included within a period.
- Voltage from
variable voltage source 908 may be applied to first plurality ofmetallic strips 928 throughvoltage lines 911. Second plurality ofmetallic strips 930 may be grounded throughvoltage lines 913. - In this illustrative example, surface waves propagated over array of radiating
elements 915 may be transmitted tophase shifter 904 as radio frequency signals by the surface wave feeds on array of radiatingelements 915. As depicted,phase shifter 904 includes plurality of phase-shiftingdevices 936. -
Transmission lines 938 couple the surface wave feeds to plurality of phase-shiftingdevices 936 and couple plurality of phase-shiftingdevices 936 toradio frequency module 906.Radio frequency module 906 may be configured to function as a transmitter, a receiver, or a combination of the two. - Turning now to
Figure 10 , an illustration ofantenna system 900 fromFigure 9 with a different voltage controller is depicted in accordance with an example. In this illustrative example,voltage controller 903 fromFigure 9 has been replaced withvoltage controller 1000.Voltage controller 1000 includesground 1002, digital toanalog converter 1004,voltage lines 1006, andvoltage lines 1008. -
Voltage lines 1006 allow second plurality ofmetallic strips 930 to be grounded toground 1002.Voltage lines 1008 supply voltage from digital toanalog converter 1004 to first plurality ofmetallic strips 928.Controller 1010 is used to control digital toanalog converter 1004. In this illustrative example, different voltages are sent to each radiating element in array of radiatingelements 915. - Further, as depicted,
phase shifter 904 is not included in this configuration forantenna system 900.Transmission lines 1012 directly coupleradio frequency module 906 to the surface wave feeds on array of radiatingelements 915. - In this illustrative example, the radiation pattern created by
antenna 902 is steered in the theta direction by controlling the voltages applied to the different varactors in array of radiatingelements 915. The radiation pattern created byantenna 902 is steered in the phi direction by the slight variations in surface wave index between neighboring radiating elements. This variation results in phase shifts between the surface waves propagated along these radiating elements, which results in steering in the phi direction. - With reference now to
Figures 11A and11B , an illustration of yet another configuration forantenna system 900 is depicted in accordance with an example. In this illustrative example,phase shifter 904 fromFigure 9 has been replaced withphase shifter 1100. -
Phase shifter 1100 may be used to control the phi steering angle forantenna system 900.Phase shifter 1100 includeswaveguides - The phase of the surface waves may be controlled such that the phase shift of the surface waves at the end of the adjacent waveguides is Δψ. The phase of the surface waves at the end of each of the waveguides is varied by controlling the propagation speed of the surface waves. The propagation speed of the surface waves may be controlled by controlling the voltage applied to the varactors on the dielectric substrates.
-
Voltage controller 1118 may be used to apply voltages to at least a portion of the metallic strips of the dielectric substrates, and thereby, at least a portion of the varactors on the dielectric substrates.Voltage controller 1118 includes digital toanalog converter 1120,voltage lines 1122, andground 1121. Voltages may be applied to at least a portion of the metallic strips on the dielectric substrates from digital toanalog converter 1120 byvoltage lines 1122. Another portion of the metallic strips may be grounded toground 1121.Controller 1123 may be used to control digital toanalog converter 1120. - The phase of the surface waves at the end of a waveguide may be given by the following equation:
voltage controller 1118 in order to create a phase difference at the surface wave feeds on the waveguides. The radio frequency signals may be sent between the surface wave feeds andradio frequency module 906 overtransmission lines 1124. - With reference now to
Figure 12 , an illustration of a portion of an antenna system is depicted in accordance with an example. In this illustrative example, a portion ofantenna system 1200 is depicted.Antenna system 1200 is an example of one implementation ofantenna system 100 inFigure 1 . As depicted,antenna system 1200 includes radiatingelement 1201 andradio frequency assembly 1202. -
Radiating element 1201 is an example of one implementation for radiatingelement 123 inFigure 1 . Further, radiatingelement 1201 is an example of an implementation for array of radiatingelements 122 inFigure 1 comprising only a single radiating element. Only a portion of radiatingelement 1201 is shown in this illustrative example. In this example, the radiation pattern produced byantenna system 1200 may only be electronically scanned in the X-Z plane. - In this illustrative example,
radio frequency assembly 1202 includesradio frequency module 1203,phase shifting device 1204,transmission line 1206,transmission line 1208,surface wave feed 1210, andsurface wave feed 1211.Radio frequency module 1203 may be configured to function as a transmitter, a receiver, or a combination of the two.Phase shifting device 1204 takes the form of a hybrid power splitter in this example. In particular, the hybrid power splitter is configured for use in varying the phase difference between the radio frequency signal traveling alongtransmission line 1206 and the radio frequency signal traveling alongtransmission line 1208. In this illustrative example, the hybrid power splitter may be used to vary the phase difference between these two transmission lines between about 0 degrees and about 90 degrees. - Of course, in other illustrative examples,
radio frequency module 1203 andphase shifting device 1204 may be implemented in some other manner. For example,radio frequency module 1203 may be configured to enable dual polarization withphase shifting device 1204 taking the form of a four port variable phase power splitter. -
Radiating element 1201 is implemented usingdielectric substrate 1205.Surface wave channel 1212 andsurface wave channel 1213 are formed ondielectric substrate 1205. Surface wave feed 1210couples transmission line 1206 to surfacewave channel 1212. Surface wave feed 1211couples transmission line 1208 to surfacewave channel 1213.Surface wave channel 1212 andsurface wave channel 1213 may be examples of implementations forsurface wave channel 125 and secondsurface wave channel 145 inFigure 1 . - As depicted,
surface wave channel 1212 is formed by plurality ofmetallic strips 1214 and plurality ofvaractors 1215. In this illustrative example, plurality ofmetallic strips 1214 are periodically arranged at an angle of about positive 45 degrees relative toX-axis 1216.X-axis 1216 is the longitudinal axis along radiatingelement 1201. Plurality ofvaractors 1215 are electrically connected to plurality ofmetallic strips 1214.Voltage lines 1218 are used to apply voltages to plurality ofvaractors 1215.Pins 1220 may be used to connectvoltage lines 1218 to one or more voltage sources and/or one or more grounds. - Further, as depicted,
surface wave channel 1213 is formed by plurality ofmetallic strips 1224 and plurality ofvaractors 1226. As depicted, plurality ofmetallic strips 1224 are periodically arranged at an angle of about negative 45 degrees relative toX-axis 1216.Voltage lines 1228 are used to apply voltages to plurality ofvaractors 1226.Pins 1230 are used to connectvoltage lines 1228 to one or more voltage sources and/or one or more grounds. - The radiation pattern formed by radiating
element 1201 may be scanned in the X-Z plane by changing the voltages applied to plurality ofvaractors 1215 such that the surface wave impedance modulation pattern results in the desired radiation angle.Surface wave channel 1212 andsurface wave channel 1213 are configured such that the radiation from these two surface wave channels may be orthogonal to each other. The net radiation from the combination of these two surface wave channels is circularly polarized. When fed byphase shifting device 1204 in the form of a 0°-90° hybrid splitter,surface wave channel 1212 andsurface wave channel 1213 are fixed into receiving or transmitting circularly-polarized radiation with either right-hand polarization or left-hand polarization. Of course, in other illustrative examples,phase shifting device 1204 may be implemented in some other manner such that the radiation may be switched between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). - The radiation from
surface wave channel 1212 andsurface wave channel 1213 is polarized because of the angles at which plurality ofmetallic strips 1214 and plurality ofmetallic strips 1224, respectively, are tilted relative toX-axis 1216. Plurality ofmetallic strips 1214 and plurality ofmetallic strips 1224 are tensor impedance elements having a major principal axis that is perpendicular to the long edges of the metallic strips and a minor axis that is along the edges. The local tensor admittance of each surface wave channel in the coordinate frame of the principal axes may be given as follows: -
-
- With reference now to
Figure 13 , an illustration ofantenna system 1200 fromFigure 12 having two radio frequency assemblies is depicted in accordance with an example. - In this illustrative example,
radio frequency assembly 1202 is located atend 1300 of radiatingelement 1201, whileradio frequency assembly 1301 is located atend 1303 of radiatingelement 1201. -
Radio frequency assembly 1301 includesradio frequency module 1302,phase shifting device 1304,transmission line 1306,transmission line 1308,surface wave feed 1310, andsurface wave feed 1312.Surface wave feed 1310 feeds intosurface wave channel 1212. Further,surface wave feed 1312 feeds intosurface wave channel 1213. - Either
radio frequency assembly 1301 orradio frequency assembly 1202 may function as a sink for any surface wave energy that is not radiated away. In this manner, surface waves may be prevented from reflecting off at the end of radiatingelement 1201, which would lead to undesired distortion of the radiation pattern. - Further, by having two radio frequency assemblies, the radiation pattern may be more effectively tuned over a larger angular range. Thus, when radiation is to be tilted towards the positive portion of
X-axis 1216,radio frequency assembly 1202 may be used to feed the radio frequency signal to radiatingelement 1201. When radiation is to be tilted towards the negative portion ofX-axis 1216,radio frequency assembly 1301 may be used to feed the radio frequency signal to radiatingelement 1201. In this manner, as the radio frequency beam formed by the radiation pattern is scanned in an angle, beams directed with angles of positive theta and negative theta may be mirror images of each other. - With reference now to
Figure 14 , an illustration of another antenna system is depicted in accordance with an example. - In this illustrative example,
antenna system 1400 is another example of one implementation forantenna system 100 inFigure 1 .Antenna system 1400 includesantenna 1401,phase shifter 1402, andradio frequency module 1404.Antenna system 1400 may also include a voltage controller (not shown in this example). -
Antenna 1401 includes array of radiatingelements 1406 and plurality of surface wave feeds 1407. Array of radiatingelements 1406 includes radiatingelements element 1201 inFigure 12 . - Plurality of surface wave feeds 1407 couple array of radiating
elements 1406 tophase shifter 1402.Phase shifter 1402 includes plurality of phase-shiftingdevices 1424.Transmission lines 1426 connect plurality of surface wave feeds 1407 to plurality of phase-shiftingdevices 1424 and connect plurality of phase-shiftingdevices 1424 toradio frequency module 1404.Radio frequency module 1404 may be configured to function as a transmitter, a receiver, or a combination of the two. - Plurality of phase-shifting
devices 1424 are variable phase shifters in this example. In this illustrative example, plurality of phase-shiftingdevices 1424 may be tuned such that the net phase shift at each one of plurality of surface wave feeds 1407 differs from the phase at a neighboring surface wave feed by a constant, Δφ. As this constant is varied, the radiation pattern formed may be scanned in the Y-Z plane. - The illustrations in
Figures 2-14 are not meant to imply physical or architectural limitations to the manner in which an illustrative example may be implemented. Other components in addition to or in place of the ones illustrated may be used. Some components may be optional. - The different components shown in
Figures 2-14 may be illustrative examples of how components shown in block form inFigure 1 can be implemented as physical structures. Additionally, some of the components inFigures 2-14 may be combined with components inFigure 1 , used with components inFigure 1 , or a combination of the two. - In some cases, it may be desirable to improve the gain of an antenna, such as artificial
impedance surface antenna 110 inFigure 1 . The gain of an artificial impedance surface antenna may be improved by improving the accuracy with which the artificial impedance surface antenna is electronically steered to reduce fall off in gain. The illustrative examples recognize and take into account that a substantially, radially symmetric arrangement of surface wave channels may allow more accurate electronic steering of the artificial impedance surface antenna. Further, with this type of arrangement, the impedance elements used to form the surface wave channels may be spaced apart greater than half a wavelength. Still further, this type of arrangement may be used to produce radiation of any polarization. - With reference now to
Figure 15 , an illustration of a different configuration for artificialimpedance surface antenna 110 inantenna system 100 fromFigure 1 is depicted in the form of a block diagram in accordance with an example.Antenna system 100 fromFigure 1 is depicted with artificialimpedance surface antenna 110 havingradial configuration 1500. - When artificial
impedance surface antenna 110 hasradial configuration 1500, artificialimpedance surface antenna 110 includesdielectric substrate 1501, plurality of radiatingspokes 1502, and number of surface wave feeds 1504.Dielectric substrate 1501 may be implemented in a manner similar todielectric substrate 124 inFigure 1 . However, withradial configuration 1500,dielectric substrate 1501 may be the only dielectric substrate used.Dielectric substrate 1501 may be comprised of any number of layers of dielectric material. - In one illustrative example,
dielectric substrate 1501 may be comprised of a material with tunable electrical properties. For example, without limitation,dielectric substrate 1501 may be comprised of a liquid crystal material. - In this illustrative example,
dielectric substrate 1501 hascircular shape 1506 withcenter point 1508. In other words,dielectric substrate 1501 may be substantially symmetric aboutcenter point 1508. In other illustrative examples,dielectric substrate 1501 may have some other shape. For example, without limitation,dielectric substrate 1501 may have an oval shape, a square shape, a hexagonal shape, an octagonal shape, or some other type of shape. However, whendielectric substrate 1501 is not substantially symmetric aboutcenter point 1508, theradiation pattern 112 produced may not have the same gain at different steering angles. - Plurality of radiating
spokes 1502 may be implemented usingdielectric substrate 1501. In particular, plurality of radiatingspokes 1502 may be formed ondielectric substrate 1501. - Plurality of radiating
spokes 1502 may be arranged radially with respect tocenter point 1508 ofdielectric substrate 1501. In these illustrative examples, being arranged radially with respect tocenter point 1508 means that each of plurality of radiatingspokes 1502 may extend fromcenter point 1508 towards an outer circumference ofdielectric substrate 1501. Each of plurality of radiatingspokes 1502 may be arranged substantially perpendicular to a center axis throughcenter point 1508 ofdielectric substrate 1501. Further, each of plurality of radiatingspokes 1502 may be arranged in a manner such that each radiating spoke is substantially symmetric aboutcenter point 1508. - Each of plurality of radiating
spokes 1502 may be implemented in a manner similar to radiatingelement 123 fromFigure 1 . Radiating spoke 1510 may be an example of one implementation for each radiating spoke in plurality of radiating spokes 1502. Radiating spoke 1510 is configured to formsurface wave channel 1512. In this manner, plurality of radiatingspokes 1502 may form a plurality of surface wave channels.Surface wave channel 1512 is configured to constrain a path of a surface wave. - As depicted, radiating spoke 1510 may include plurality of
impedance elements 1514 and plurality oftunable elements 1516. Plurality ofimpedance elements 1514 and plurality oftunable elements 1516 may be implemented in a manner similar to plurality ofimpedance elements 126 and plurality oftunable elements 128, respectively, fromFigure 1 . - In this illustrative example, plurality of
impedance elements 1514 and plurality oftunable elements 1516 may be located onsurface 1513 ofdielectric substrate 1501. In particular, plurality ofimpedance elements 1514 and plurality oftunable elements 1516 may be located onsurface 1513 of correspondingportion 1515 ofdielectric substrate 1501. - Plurality of
impedance elements 1514, plurality oftunable elements 1516, and correspondingportion 1515 ofdielectric substrate 1501 may form an artificial impedance surface from which radiation may be generated. In this illustrative example, correspondingportion 1515 ofdielectric substrate 1501 may be considered part of radiatingspoke 1510. However, in other illustrative examples,dielectric substrate 1501 may be considered separate from plurality of radiating spokes 1502. - An impedance element in plurality of
impedance elements 1514 may be implemented in a number of different ways. In one illustrative example, an impedance element may be implemented as a resonating element. In one illustrative example, an impedance element may be implemented as an element comprised of a conductive material. The conductive material may be, for example, without limitation, a metallic material. Depending on the implementation, an impedance element may be implemented as a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate, or some other type of conductive element. In some cases, an impedance element may be implemented as a resonant structure such as, for example, a split-ring resonator (SRR), an electrically-coupled resonator (ECR), a structure comprised of one or more metamaterials, or some other type of structure or element. - Each one of plurality of
tunable elements 1516 may be an element that can be controlled, or tuned, to change an angle ofradiation pattern 112 produced by radiatingspoke 1510. In this illustrative example, each of plurality oftunable elements 1516 may be an element having a capacitance that can be varied based on the voltage applied to the tunable element. - In one illustrative example, plurality of
impedance elements 1514 takes the form of plurality ofmetallic strips 1518 and plurality oftunable elements 1516 takes the form of plurality ofvaractors 1520. Each of plurality ofvaractors 1520 may be a semiconductor element diode that has a capacitance dependent on the voltage applied to the semiconductor element diode. - Plurality of
metallic strips 1518 may be arranged in a row on correspondingportion 1515 ofdielectric substrate 1501 substantially parallel to a plane that is substantially perpendicular to a center axis throughcenter point 1508 ofdielectric substrate 1501. For example, plurality ofmetallic strips 1518 may be periodically distributed on correspondingportion 1515 ofdielectric substrate 1501 along an axis that is substantially perpendicular to and that passes through the center axis throughdielectric substrate 1501. - In some illustrative examples, plurality of
metallic strips 1518 may be printed ontodielectric substrate 1501. For example, plurality ofmetallic strips 1518 may be printed ontodielectric substrate 1501 using any number of three-dimensional printing techniques, additive deposition techniques, inkjet deposition techniques, or other types of printing techniques. - Plurality of
varactors 1520 may be electrically connected to plurality ofmetallic strips 1518 onsurface 1513 of correspondingportion 1515 ofdielectric substrate 1501. As one illustrative example, at least one varactor in plurality ofvaractors 1520 may be positioned between each adjacent pair of metallic strips in plurality ofmetallic strips 1518. Further, plurality ofvaractors 1520 may be aligned such that all of the varactor connections on each metallic strip have the same polarity. - Voltages may be applied to plurality of
tunable elements 1516 by applying voltages to plurality ofimpedance elements 1514. In particular, varying the voltages applied to plurality ofimpedance elements 1514 varies the capacitance of plurality oftunable elements 1516. Varying the capacitances of plurality oftunable elements 1516 may vary, or modulate, the capacitive coupling and impedance between plurality ofimpedance elements 1514. - Corresponding
portion 1515 ofdielectric substrate 1501, plurality ofimpedance elements 1514, and plurality oftunable elements 1516 may be configured with respect to selecteddesign configuration 1522 forsurface wave channel 1512 formed by radiatingspoke 1510. Depending on the implementation, each radiating spoke in plurality of radiatingspokes 1502 may have a same or different selected design configuration. - As depicted, selected
design configuration 1522 for radiatingspoke 1510 may include a number of design parameters such as, but not limited to,impedance element width 1524,impedance element spacing 1526,tunable element spacing 1528, andsubstrate thickness 1530.Impedance element width 1524 may be the width of an impedance element in plurality ofimpedance elements 1514.Impedance element width 1524 may be selected to be the same or different for each of plurality ofimpedance elements 1514, depending on the implementation. -
Impedance element spacing 1526 may be the spacing of plurality ofimpedance elements 1514 alongsurface 1513 of correspondingportion 1515 ofdielectric substrate 1501.Tunable element spacing 1528 may be the spacing of plurality oftunable elements 1516 alongsurface 1513 of correspondingportion 1515 ofdielectric substrate 1501. Further,substrate thickness 1530 may be the thickness of correspondingportion 1515 ofdielectric substrate 1501. In this illustrative example, an entirety ofdielectric substrate 1501 may have a substantially same thickness. However, in other illustrative examples, the different portions ofdielectric substrate 1501 corresponding to the different radiating spokes in plurality of radiatingspokes 1502 may have different thicknesses. - The values for the different parameters in selected
design configuration 1522 may be selected based on, for example, without limitation, the radiation frequency at which artificialimpedance surface antenna 110 is configured to operate. Other considerations include, for example, the desired impedance modulations for artificialimpedance surface antenna 110. - The surface waves propagated along each of plurality of radiating
spokes 1502 may be coupled to number oftransmission lines 156 by number of surface wave feeds 1504 located ondielectric substrate 1501. Each of number of surface wave feeds 1504 couples at least one corresponding radiating spoke in plurality of radiatingspokes 1502 to a transmission line that carries a radio frequency signal, such as one of number oftransmission lines 156. - A surface wave feed in number of surface wave feeds 1504 may be any device that is capable of converting a surface wave into a radio frequency signal, a radio frequency signal into a surface wave, or both. In one illustrative example, a surface wave feed in number of surface wave feeds 1504 may be located substantially at
center point 1508 ofdielectric substrate 1501. - In one illustrative example, number of surface wave feeds 1504 takes the form of a single surface wave feed positioned at
center point 1508 ofdielectric substrate 1501. This single surface wave feed, which may be referred to as a central feed, may couple each of plurality of radiatingspokes 1502 to number oftransmission lines 156. In this example, number oftransmission lines 156 may take the form of a coaxial cable. - In another illustrative example, number of surface wave feeds 1504 may take the form of a plurality of surface wave feeds located at or
near center point 1508 and configured to couple plurality of radiatingspokes 1502 to number oftransmission lines 156. In this example, number oftransmission lines 156 may take the form of a single transmission line or a plurality of transmission lines. - When artificial
impedance surface antenna 110 is in a receiving mode, electromagnetic radiation received at artificialimpedance surface antenna 110 may be propagated as surface waves along plurality of radiating spokes 1502. These surface waves are received by number of surface wave feeds 1504 and converted into number of radio frequency signals 1532. Number ofradio frequency signals 1532 may be sent toradio frequency module 108 over one or more of number oftransmission lines 156.Radio frequency module 108 may then process number ofradio frequency signals 1532 accordingly. - When artificial
impedance surface antenna 110 is in a transmitting mode, number ofradio frequency signals 1532 may be sent fromradio frequency module 108 to artificialimpedance surface antenna 110 over number oftransmission lines 156. In particular, number ofradio frequency signals 1532 may be received at number of surface wave feeds 1504 and converted into surface waves that are propagated along plurality of radiating spokes 1502. -
Radiation pattern 112 of artificialimpedance surface antenna 110 may be electronically steered in both a theta direction and a phi direction.Radiation pattern 112 may be formed by number ofradiation sub-patterns 1533. Number ofradiation sub-patterns 1533 may be produced by a corresponding portion of plurality of radiating spokes 1502. This corresponding portion may be one or more of plurality of radiating spokes 1502. In some cases, number ofradiation sub-patterns 1533 may be produced by all of plurality of radiating spokes 1502. - For example, number of
radiation sub-patterns 1533 may be produced by a corresponding number of radiating spokes in plurality of radiating spokes 1502. Each of number ofradiation sub-patterns 1533 is the radiation pattern produced by a particular radiating spoke. Number of radiating sub-patterns 1533 formsradiation pattern 112. For example, when number of radiating sub-patterns 1533 includes multiple radiating sub-patterns corresponding to multiple radiating spokes, the combination and overlapping of these multiple radiation sub-patterns formsradiation pattern 112. - In this illustrative example, each of plurality of radiating
spokes 1502 may be independently controlled such that each of number ofradiation sub-patterns 1533 may be electronically steered. For example, without limitation, radiating spoke 1510 may haveradiation sub-pattern 1534.Radiation sub-pattern 1534 may be controlled independently of the other radiation sub-patterns formed by the other radiating spokes in plurality of radiating spokes 1502. - As one illustrative example,
voltage controller 104 may be used to control the voltages applied to plurality oftunable elements 1516 to control both the theta and phi steering angles of a main lobe ofradiation sub-pattern 1534. Similarly,voltage controller 104 may be configured to control the voltages applied to the plurality of tunable elements in each of plurality of radiating spoke 1502 to control both the theta and phi steering angles of a main lobe of the radiation sub-pattern formed by each of plurality of radiating spokes 1502. - Thus, each of number of
radiation sub-patterns 1533 may be directed in a particular theta direction and a broad phi direction. For example, a particular radiation sub-pattern may be directed at a theta steering angle of about 45 degrees and may fan out over a broad range of phi angles. In this manner, each radiation sub-pattern may form, for example, a fan beam. - Number of
radiation sub-patterns 1533 overlap to formradiation pattern 112 havingmain lobe 116 directed in a particular phi direction and a particular theta direction.Radiation pattern 112 may be formed such that a beam of radiation is produced. The beam may take the form of, for example, a pencil beam that is directed at a particularphi steering angle 118 and a particulartheta steering angle 120. In this manner, artificialimpedance surface antenna 110 may be electronically steered in two dimensions. - Depending on the implementation, artificial
impedance surface antenna 110 may be configured to emit linearly polarized radiation or circularly polarized radiation. In other words, artificialimpedance surface antenna 110 may be used to produceradiation pattern 112 that is linearly polarized or circularly polarized. Further,radiation pattern 112 may be switched between being linearly polarized and circularly polarized by adjusting the voltages applied to plurality oftunable elements 1516 and without needing to change a physical configuration of artificialimpedance surface antenna 110. - The impedance sub-patterns produced by the surface wave channels formed by plurality of radiating
spokes 1502 may be modulated to produceoverall radiation pattern 112 that is linearly polarized. For example, the voltages applied to the tunable elements of each of a corresponding portion of plurality of radiatingspokes 1502 may be set such that the impedance sub-pattern produced along the surface wave channel formed by each radiating spoke is given as follows:impedance surface antenna 110, and Z(r,Ø SWC ) is the impedance sub-pattern produced along the surface wave channel. This impedance sub-pattern may produce radiation that is linearly polarized in the direction of the theta unit vector, θ̂, where: - In other examples, the impedance sub-patterns of the surface wave channels formed by plurality of radiating
spokes 1502 may be modulated to produceoverall radiation pattern 112 that is circularly polarized. The voltages applied to the tunable elements of each of a corresponding portion of plurality of radiatingspokes 1502 may be set such that the impedance sub-pattern produced by the surface wave channel formed by each radiating spoke is given as follows: -
- In other illustrative examples, the impedance sub-patterns may be given by other types of equations involving periodic functions. For example, the sine function of sin(γ ± ϕ) in Equation (19), the sine function of sin(γ ± γ 0) in Equation (15), and the cosine function of cos(k 0 r(n 0-cos(Ø swc -Ø0)sin(θ0)) in Equation (13) may each be replaced by some other type of periodic function.
- In this manner, artificial
impedance surface antenna 110 may be used to produce radiation of any polarization without requiring a change in the physical configuration of artificialimpedance surface antenna 110. Artificialimpedance surface antenna 110 may be used to produce linearly polarized or circularly polarized radiation just by changing the voltages applied to the tunable elements of plurality of radiating spokes 1502. - Depending on the implementation, artificial
impedance surface antenna 110 may propagate surface waves towards or away fromcenter point 1508 ofdielectric substrate 1501. In some illustrative examples, artificialimpedance surface antenna 110 may includeabsorption material 1536 when the surface waves are propagated away fromcenter point 1508.Absorption material 1536 may be located at and around an edge ofdielectric substrate 1501.Absorption material 1536 is configured to absorb excess energy from the surface waves propagated radially outward away fromcenter point 1508 through plurality of radiating spokes 1502. - In some illustrative examples,
dielectric substrate 1501 may be grounded usinggrounding element 1538. In particular, groundingelement 1538 may be located at an impedance surface ofdielectric substrate 1501. - The illustration of
antenna system 100 inFigure 1 is not meant to imply physical or architectural limitations to the manner in which an illustrative example may be implemented. Other components in addition to or in place of the ones illustrated may be used. Some components may be optional. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative example. - In some illustrative examples, a tunable element in plurality of
tunable elements 1516 may be implemented as a pocket of variable material embedded indielectric substrate 1501. - In other illustrative examples, a tunable element in plurality of
tunable elements 1516 may be part of a corresponding impedance element in plurality ofimpedance elements 1514. For example, a resonant structure having a tunable element may be used. The resonant structure may be, for example, without limitation, a split-ring resonator, an electrically-coupled resonator, or some other type of resonant structure. - In other illustrative examples,
center point 1508 may be the center point about which plurality of radiatingspokes 1502 are arranged but may not be the geometric center ofdielectric substrate 1501. For example,center point 1508 may be offset from the geometric center ofdielectric substrate 1501. - In yet other illustrative examples, each of plurality of radiating
spokes 1502 may have two independently controllable portions configured to form a surface wave channel. For example, radiating spoke 1510 may have a first portion that extends in one direction away fromcenter point 1508 and a second portion that extends in the substantially opposite direction away fromcenter point 1508. These two portions may have a same or different design configuration, depending on the implementation. Further, these two portions may be individually referred to as radiating spokes or radiating sub-spokes in some cases. With reference now toFigure 16 , an illustration of an artificial impedance surface antenna is depicted in accordance with an example. - In this illustrative example, artificial
impedance surface antenna 1600 may be an example of one implementation for artificialimpedance surface antenna 110 havingradial configuration 1500 inFigure 15 . Artificialimpedance surface antenna 1600 hasradial configuration 1601, which may be an example of one implementation forradial configuration 1500 inFigure 15 . - As depicted, artificial
impedance surface antenna 1600 includesdielectric substrate 1602, centralsurface wave feed 1604, and plurality of radiating spokes 1606.Dielectric substrate 1602, centralsurface wave feed 1604, and plurality of radiatingspokes 1606 may be examples of implementations fordielectric substrate 1501, number of surface wave feeds 1504, and plurality of radiatingspokes 1502, respectively, inFigure 15 . - In this illustrative example,
dielectric substrate 1602 has a circular shape withcenter point 1605. Plurality of radiatingspokes 1606 are arranged radially with respect tocenter point 1605 such that artificialimpedance surface antenna 1600 is substantially radially symmetric. Radiating spoke 1608, radiating spoke 1610, radiating spoke 1612, and radiating spoke 1614 may be examples of some of plurality of radiating spokes 1606. Plurality of radiatingspokes 1606 are formed byimpedance elements 1616 that have been printed ondielectric substrate 1602.Impedance elements 1616 take the form of metallic strips in this illustrative example. Plurality of radiatingspokes 1606 may also include tunable elements (not shown in this view) located betweenimpedance elements 1616. - Central
surface wave feed 1604 may couple plurality of radiatingspokes 1606 to a transmission line (not shown in this view). The transmission line may be configured to carry a radio frequency to, from, or both to and from centralsurface wave feed 1604. Artificialimpedance surface antenna 1600 may be electronically steered with a desired level of accuracy in a theta direction and a phi direction. Each of plurality of radiatingspokes 1606 may be individually electronically steered in a particular theta direction and a broad phi direction to produce a fan beam. For example, radiating spoke 1608, radiating spoke 1612, and radiating spoke 1614 may be electronically steered to producefan beam 1618,fan beam 1620, andfan beam 1622, respectively. The radiation patterns corresponding tofan beam 1618,fan beam 1620, andfan beam 1622 may overlap such thatpencil beam 1624 is produced.Pencil beam 1624 may be directed at a particular theta steering angle and a particular phi steering angle. - As depicted,
absorption material 1626 is located at and around an outer edge ofdielectric substrate 1602.Absorption material 1626 may be an example of one implementation forabsorption material 1536 inFigure 15 .Absorption material 1626 is configured to absorb excess energy resulting from surface waves propagating away fromcenter point 1605. With reference now toFigure 17 , an illustration of a cross-sectional side view of artificialimpedance surface antenna 1600 fromFigure 16 is depicted in accordance with an illustrative example. - In this illustrative example, a cross-sectional side view of artificial
impedance surface antenna 1600 fromFigure 16 is depicted taken with respect to cross-section lines 17-17 inFigure 17 . - In this illustrative example, grounding
element 1700 may be seen along the surface ofdielectric substrate 1602.Grounding element 1700 is an example of one implementation forgrounding element 1538 inFigure 15 . -
Transmission line 1702 is also shown in this view.Transmission line 1702 may carry a radio frequency to, from, or both to and from centralsurface wave feed 1604. In one illustrative example,transmission line 1702 takes the form of a coaxial cable. - As depicted, surface waves may propagate in the direction of
arrow 1704, substantially parallel todielectric substrate 1602 and substantially perpendicular tocenter axis 1706 throughcenter point 1605 ofdielectric substrate 1602. Plurality of radiating spokes 1606 (not shown in this view) may be arranged such that plurality of radiatingspokes 1606 are substantially symmetric aboutcenter axis 1706. - With reference now to
Figure 18 , an illustration of an impedance pattern for artificialimpedance surface antenna 1600 fromFigures 16-17 is depicted in accordance with an example. - In this illustrative example,
impedance pattern 1800 may be produced when artificialimpedance surface antenna 1600 is linearly polarized and configured to produce a radiation pattern having a main lobe directed at a theta steering angle of about 45 degrees and a phi steering angle of about 0 degrees. -
Impedance pattern 1800 is shown with respect tofirst axis 1802 andsecond axis 1804.First axis 1802 andsecond axis 1804 may represent the two axes that form the plane substantially parallel todielectric substrate 1602 inFigure 16 .Impedance pattern 1800 is comprised ofimpedance sub-patterns 1806 formed by plurality of radiatingspokes 1606 inFigures 16 .Scale 1808 provides the correlation between the impedance sub-patterns 1806 and impedance values. The impedance values may be in units of j-Ohms in which j is equal to - With reference now to
Figure 19 , an illustration of a portion of an artificial impedance surface antenna is depicted in accordance with an example. In this illustrative example, artificialimpedance surface antenna 1900 may be another example of one implementation for artificialimpedance surface antenna 110 havingradial configuration 1500 inFigure 15 . Artificialimpedance surface antenna 1900 hasradial configuration 1901, which may be an example of one implementation forradial configuration 1500 inFigure 15 . - In this illustrative example, artificial
impedance surface antenna 1900 includesdielectric substrate 1902, radiatingspokes 1904, and centralsurface wave feed 1906. Only a portion of the total plurality of radiating spokes that form artificialimpedance surface antenna 1900 are shown in this view. - Radiating spoke 1907 is an example of one of radiating spokes 1904. Only a portion of radiating spoke 1907 is shown. Radiating spoke 1907 is located on corresponding
portion 1908 ofdielectric substrate 1902. Radiating spoke 1907 includes plurality ofmetallic strips 1909 and plurality ofvaractors 1910. Plurality ofmetallic strips 1909 and plurality ofvaractors 1910 may be an example of one implementation for plurality ofmetallic strips 1518 and plurality ofvaractors 1520, respectively, inFigure 15 . - As depicted, voltages may be applied to plurality of
metallic strips 1909, and thereby plurality ofvaractors 1910, throughconductive lines 1912, which terminate atterminals 1914.Terminals 1914 may be connected to electrical vias (not shown in this view) that pass through the thickness ofdielectric substrate 1902 and through a grounding element (not shown in this view) to connectors that connect to control hardware, such as a voltage controller. - With reference now to
Figure 20 , an illustration of a cross-sectional side view of artificialimpedance surface antenna 1900 fromFigure 19 is depicted in accordance with an example. - In this illustrative example, a cross-sectional side view of artificial
impedance surface antenna 1900 fromFigure 19 is depicted taken with respect to cross-section lines 20-20 inFigure 19 . - In this illustrative example,
electrical vias 2000 that connectterminals 1914 inFigure 19 tovoltage controller 2002 are shown.Voltage controller 2002 may vary the voltages applied to the metallic strips of plurality of radiatingspokes 1904 inFigure 19 . - The illustrative embodiments recognize and take into account that different types of configurations for artificial
impedance surface antenna 110 inFigure 1 may improve the efficiency and thereby, overall performance, of artificialimpedance surface antenna 110. - The illustrative embodiments recognize and take into account that in some cases, it may be desirable to provide a square-wave-type profile of surface impedance across each surface wave channel formed on each radiating element of artificial
impedance surface antenna 110 inFigure 1 . - The illustrative embodiments recognize that using switch elements that have only two possible states as compared to varactors that can be tuned to have any of various capacitance states across a range of capacitance values may enable achieving a square-wave-type profile of surface impedance for a surface wave channel. These switch elements may take the form of, for example, without limitation, PIN diodes.
- With reference now to
Figure 21 , an illustration of artificialimpedance surface antenna 110 fromFigure 1 is depicted in the form of a block diagram in accordance with an illustrative embodiment. In this illustrative embodiment, at least one surface wave channel on at least one radiating element in artificialimpedance surface antenna 110 inFigure 21 is implemented differently than as described inFigure 1 . As depicted,surface wave channel 125 fromFigure 1 does not include plurality oftunable elements 128 fromFigure 1 . Rather, in this illustrative embodiment,surface wave channel 125 includes plurality ofswitch elements 2100 instead of plurality oftunable elements 128 fromFigure 1 . Each of plurality ofswitch elements 2100 has only twostates 2102. - Two
states 2102 may includefirst state 2104 andsecond state 2106. In some cases,first state 2104 may be referred to as an on state andsecond state 2106 may be referred to as an off state. - In one illustrative embodiment, plurality of
switch elements 2100 takes the form of plurality ofPIN diodes 2108. In other illustrative embodiments, a switch element in plurality ofswitch elements 2100 is selected from one of a semiconductor switch, a microelectromechanical systems (MEMS) switch, a high frequency diode, a Schottky diode, and a phase-change material switch. -
Switch element 2101 may be an example of one of plurality ofswitch elements 2100. -
Switch element 2101 is placed within the gap betweenfirst impedance element 2113 of plurality ofimpedance elements 126 andsecond impedance element 2115 of plurality ofimpedance elements 126. Further,switch element 2101 electrically connectsfirst impedance element 2113 tosecond impedance element 2115. The capacitance ofswitch element 2101 and the capacitance of the gap betweenfirst impedance element 2113 andsecond impedance element 2115 contribute to the total capacitance betweenfirst impedance element 2113 andsecond impedance element 2115. In some cases, the capacitance of the gap betweenfirst impedance element 2113 andsecond impedance element 2115 may be negligible. - When
switch element 2101 takes the form of a PIN diode,first state 2104 may take the form ofinductance state 2105 andsecond state 2106 may take the form ofcapacitance state 2107.Switch element 2101 may be placed ininductance state 2105 by applying a first level of voltage to switchelement 2101.Switch element 2101 may be placed incapacitance state 2107 by applying a second level of voltage to switchelement 2101. - Whether
switch element 2101 is ininductance state 2105 or incapacitance state 2107 may be determined by the reactance ofswitch element 2101. For example, the surface impedance associated withswitch element 2101 may be defined as follows:switch element 2101 may be considered ininductance state 2105. When the reactance is negative, the reactance is described as capacitive andswitch element 2101 may be considered incapacitance state 2107. When the reactance is substantially zero, the surface impedance may be considered substantially purely resistive. - In
inductance state 2105,switch element 2101 may have substantially zero capacitance but may have parasitic inductance. In other words, the capacitance ofswitch element 2101 may be zero or negligible whenswitch element 2101 is ininductance state 2105. In this manner, ininductance state 2105,switch element 2101 may be modeled as a series resistor-inductor circuit. Incapacitance state 2107,switch element 2101 may have some selected non-zero capacitance value. In this manner, incapacitance state 2107,switch element 2101 may be modeled as a parallel resistor-capacitor circuit. - Because each of plurality of
switch elements 2100 may have only one of twostates 2102 at any given point in time, the voltages applied to plurality ofswitch elements 2100 may be used to createsurface impedance profile 2114 forsurface wave channel 125. In particular, one of two levels of voltage may be applied to each of plurality ofswitch elements 2100 to createsurface impedance profile 2114.Surface impedance profile 2114 may be created such that only a selected high surface impedance, a selected low surface impedance, or some combination of the two is formed. - For example, without limitation, the voltages applied to plurality of
switch elements 2100 may be controlled such thatsurface impedance profile 2114 takes the form of square-wave modulation 2110 of high surface impedance and low surface impedance. Square-wave modulation 2110 may be a square-wave-type modulation. In other words, in one illustrative example, the state of each of plurality ofswitch elements 2100 may be controlled to modulate high surface impedance and low surface impedance in the form of a square-wave as compared to a sinusoidal wave. These two surface impedance levels may be modulated over each surface wave channel on each radiating element of artificialimpedance surface antenna 110 to electronically steer artificialimpedance surface antenna 110 in a theta direction, a phi direction, or both. - In one illustrative example, each of plurality of
impedance elements 126 may take the form of a rectangular metallic strip. In some illustrative embodiments, each of plurality ofimpedance elements 126 has a shape that has repeatingpattern 2112.Repeating pattern 2112 may be a pattern of shapes. In some illustrative embodiments, a particular impedance element of plurality ofimpedance elements 126 has a repeating pattern of a same shape that hexagonal-type shape. In some excamples, the shape may be a diamond-type shape, or some other type of shape. - Using plurality of
switch elements 2100 forsurface wave channel 125 may improve the gain of artificialimpedance surface antenna 110. Further, using plurality ofswitch elements 2100 may enable artificialimpedance surface antenna 110 to be operated at a frequency in the Ka-band with a desired level of aperture efficiency. In this manner, using plurality ofswitch elements 2100 may reduce power loss. The Ka-band may include frequencies between about 26.5 gigahertz and about 40 gigahertz. As one illustrative example, using plurality ofPIN diodes 2108 may enable artificialimpedance surface antenna 110 to be operated at a frequency of about 30 gigahertz with greater than about 25 percent aperture efficiency. - The illustration of artificial
impedance surface antenna 110 inFigure 21 is not meant to imply physical or architectural limitations to the manner in which an illustrative embodiment may be implemented. Other components in addition to or in place of the ones illustrated may be used. Some components may be optional. Also, the blocks are presented to illustrate some functional components. One or more of these blocks may be combined, divided, or combined and divided into different blocks when implemented in an illustrative embodiment. - With reference now to
Figure 22 , an illustration of a radiating element is depicted in accordance with an illustrative embodiment. In this illustrative embodiment, radiatingelement 2200 is one implementation for radiatingelement 123 inFigure 21 . - As depicted, radiating
element 2200 includesdielectric substrate 2202.Surface wave channel 2204 is formed ondielectric substrate 2202.Surface wave channel 2204 is one implementation forsurface wave channel 125 inFigure 21 . - In this illustrative embodiment,
surface wave channel 2204 comprises plurality ofimpedance elements 2206 and plurality ofswitch elements 2208. Plurality ofswitch elements 2208 are one implementation for plurality ofswitch elements 2100 inFigure 21 . - Each of plurality of
switch elements 2208 has only one of two states at any given point in time in this illustrative embodiment. For example, when one of plurality ofswitch elements 2208 is in an on state, the switch element may function in a manner similar to a circuit comprising a resistor and inductor in series. The on state corresponds to high surface impedance. The inductance that is provided may be important to enable operation of the artificial surface impedance antenna to whichsurface wave channel 2204 belongs within the Ka-band of frequencies. When the switch element is in an off state, the switch element may function in a manner similar to a circuit comprising a resistor and capacitor in parallel. The off state corresponds to low surface impedance. - The state of each of plurality of
switch elements 2208 is controlled to modulate between high surface impedance and low surface impedance to create a surface impedance profile forsurface wave channel 2204. This surface impedance profile may resemble a square-wave-type modulation.Portion 2210 ofsurface wave channel 2204 is shown enlarged inFigure 23 below. - With reference now to
Figure 23 , an illustration of an enlarged view ofportion 2210 ofsurface wave channel 2204 fromFigure 22 is depicted in accordance with an illustrative embodiment. As depicted, plurality ofimpedance elements 2206 includesimpedance element 2300 andimpedance element 2302.Impedance element 2300 andimpedance element 2302 are implementations forfirst impedance element 2113 andsecond impedance element 2115, respectively, fromFigure 21 . - Plurality of
switch elements 2208 includes set ofswitch elements 2304 positioned within the gap betweenimpedance element 2300 andimpedance element 2302. Each of set ofswitch elements 2304 has only two possible states and may be in only one of these two possible states at any given point in time. In one illustrative example, these two states may be an inductance state and a capacitance state. - As depicted, set of
switch elements 2304 includesswitch element 2306,switch element 2308, andswitch element 2310.Switch element 2306,switch element 2308, andswitch element 2310 electrically connectimpedance element 2300 andimpedance element 2302. - Each of plurality of
impedance elements 2206 inFigure 22 has a repeating pattern of shapes.Impedance element 2302 has repeatingpattern 2312.Repeating pattern 2312 is a series of same shapes.Repeating pattern 2312 is a series of hexagonal-type shapes. As depicted, repeatingpattern 2312 includes hexagonal-type shape 2314, hexagonal-type shape 2316, and hexagonal-type shape 2318. - With reference now to
Figure 24 , an illustration of another configuration for a radiating element is depicted in accordance with an illustrative example. In this illustrative example, radiatingelement 2400 may be an example of one implementation for radiatingelement 123 inFigure 21 . - As depicted, radiating
element 2400 includesdielectric substrate 2402.Surface wave channel 2404 is formed ondielectric substrate 2402.Surface wave channel 2404 may be an example of one implementation forsurface wave channel 125 inFigure 21 .Surface wave channel 2404 comprises plurality ofimpedance elements 2406 and plurality ofswitch elements 2408. - Plurality of
impedance elements 2406 may be an example of one implementation for plurality ofimpedance elements 126 inFigure 1 . In this illustrative example, each of plurality ofimpedance elements 2406 may take the form of a rectangular metallic strip. Plurality ofswitch elements 2408 may be an example of one implementation for plurality ofswitch elements 2100 inFigure 21 . In this illustrative example, each of plurality ofswitch elements 2408 may have only one of two states at any given point in time. In one illustrative example, each of plurality ofswitch elements 2408 may be implemented in the form of a PIN diode. - For example, when one of plurality of
switch elements 2408 is in an on state, the switch element may function in a manner similar to a circuit comprising a resistor and inductor in series. The on state corresponds to high surface impedance. The inductance that is provided may be important to enable operating within the Ka-band of frequencies. When the switch element is in an off state, the switch element may function in a manner similar to a circuit comprising a resistor and capacitor in parallel. The off state corresponds to low surface impedance. - Turning now to
Figure 25 , an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative example. - The process illustrated in
Figure 25 may be implemented to electronically steerantenna system 100 inFigure 1 . - The process begins by propagating a surface wave along each of a number of surface wave channels formed in each of a plurality of radiating elements to form a radiation pattern (operation 2500). Each surface wave channel in the number of surface wave channels formed in each radiating element in the plurality of radiating elements is coupled to a transmission line configured to carry a radio frequency signal using a surface wave feed in a plurality of surface wave feeds associated with the plurality of radiating elements (operation 2502).
- Thereafter, a main lobe of the radiation pattern is electronically steered in a theta direction by controlling voltages applied to the number of surface wave channels in each radiating element in the plurality of radiating elements (operation 2504). Further, the main lobe of the radiation pattern is electronically steered in a phi direction by controlling a relative phase difference between the plurality of surface wave feeds (operation 2506), with the process terminating thereafter.
- With reference now to
Figure 26 , an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative example. - The process illustrated in
Figure 26 may be implemented to electronically steer, for example, artificialimpedance surface antenna 110 havingradial configuration 1500 inFigure 15 . - The process begins by propagating a surface wave along a plurality of surface wave channels formed by a plurality of radiating spokes in an antenna to generate a number of radiation sub-patterns in which the plurality of radiating spokes is arranged radially with respect to a center point of a dielectric substrate (operation 2600). Next, a main lobe of a radiation pattern of the antenna is electronically steered in two dimensions (operation 2602), with the process terminating thereafter.
- With reference now to
Figure 27 , an illustration of a process for electronically steering an antenna system is depicted in the form of a flowchart in accordance with an illustrative embodiment. The process illustrated inFigure 27 may be implemented to electronically steer, for example, artificialimpedance surface antenna 110 having switch elements as described inFigure 21 . - The process begins by propagating a surface wave along each of a number of surface wave channels formed in each of a plurality of radiating elements to form a radiation pattern (operation 2700). Next, each surface wave channel in the number of surface wave channels formed in each radiating element in the plurality of radiating elements may be coupled to a transmission line configured to carry a radio frequency signal using a surface wave feed in a plurality of surface wave feeds associated with the plurality of radiating elements (operation 2702).
- A main lobe of the radiation pattern may be electronically steered by controlling voltages applied to a plurality of switch elements connecting a plurality of impedance elements in each of the number of surface wave channels (operation 2704), with the process terminating thereafter.
- The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatuses and methods in an illustrative embodiment. In this regard, each block in the flowcharts or block diagrams may represent a module, a segment, a function, and/or a portion of an operation or step.
- In some alternative implementations of an illustrative embodiment, the function or functions noted in the blocks may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved. Also, other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.
Claims (14)
- An apparatus comprising:
a plurality of radiating elements, wherein each radiating element (123) in the plurality of radiating elements comprises a number of surface wave channels in which each (125) of the number of surface wave channels is configured to constrain a path of a surface wave and comprises:a plurality of switch elements (2100); anda plurality of impedance elements (126); anda surface wave feed configured to couple a surface wave channel (125) in the number of surface wave channels of a radiating element (123) in the plurality of radiating elements to a transmission line configured to carry a radio frequency signal (154),wherein the plurality of impedance elements (126) in each (125) of the number of surface wave channels are arranged in a repeating hexagonal-type pattern, andwherein each switch element (2101) is positioned within a gap between a first impedance element (2113) of the plurality of impedance elements (126) and a second impedance element (2115) of the plurality of impedance elements (126), and wherein the switch element (2101) electrically connects the first impedance element (2113) to the second impedance element (2115). - The apparatus of claim 1, wherein the plurality of radiating elements form an artificial impedance surface antenna (110) that is configured to be electronically steered in an elevation direction and an azimuth direction.
- The apparatus of claim 2, wherein the artificial impedance surface antenna (110) is configured to operate at a frequency between about 26.5 gigahertz and about 40 gigahertz.
- The apparatus of any of claims 2-3, wherein the plurality of switch elements (2100) of each surface wave channel (125) of the number of surface wave channels are configured to create a surface impedance profile (2114) of high surface impedance and low surface impedance for the each surface wave channel (125).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a PIN diode that has an inductance state (2105) and a capacitance state (2107).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a Schottky diode that has only two states (2102).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a semiconductor switch that has only two states (2102).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a microelectromechanical systems switch diode that has only two states (2102).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a phase-change material switch that has only two states (2102).
- The apparatus of any of claims 1-2, wherein each switch element (2101) in the plurality of switch elements (2100) is a high frequency diode that has only two states (2102).
- The apparatus of any of claims 1, 2, or 5-10, wherein an impedance element in the plurality of impedance elements (126) is selected from one of a metallic strip, a patch of conductive paint, a metallic mesh material, a metallic film, a deposit of a metallic substrate, a resonant structure, a split-ring resonator, and an electrically-coupled resonator, a structure comprised of one or more metamaterials.
- A method for electronically steering an antenna system (100), the method comprising:propagating (2700) a surface wave along each of a number of surface wave channels formed in each of a plurality of radiating elements to form a radiation pattern (112);coupling (2702) each surface wave channel (125) in the number of surface wave channels formed in each radiating element (123) in the plurality of radiating elements to a transmission line configured to carry a radio frequency signal (154) using a surface wave feed in a plurality of surface wave feeds (130) associated with each of the number of surface wave channels; andelectronically steering (2704) a main lobe (116) of the radiation pattern (112) by controlling voltages applied to a plurality of switch elements (2100) connecting a plurality of impedance elements (126) in each (125) of the number of surface wave channels,wherein the plurality of impedance elements (126) in each (125) of the number of surface wave channels are arranged in a repeating hexagonal-type pattern, andwherein each switch element (2101) is positioned within a gap between a first impedance element (2113) of the plurality of impedance elements (126) and a second impedance element (2115) of the plurality of impedance elements (126), and wherein the switch element (2101) electrically connects the first impedance element (2113) to the second impedance element (2115)
- The method of claim 12, wherein electronically steering the main lobe (116) comprises:
applying a first level of voltage or a second level of voltage to each of the plurality of switch elements (2100) to create a surface impedance profile (2114) for each surface wave channel (125) of the number of surface wave channels. - The method of claim 13, wherein applying a first level of voltage or a second level of voltage to each of the plurality of switch elements (2100) modulates the surface impedance profile between high surface impedance and low surface impedance.
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US3959794A (en) * | 1975-09-26 | 1976-05-25 | The United States Of America As Represented By The Secretary Of The Army | Semiconductor waveguide antenna with diode control for scanning |
DE19958750B4 (en) * | 1999-12-07 | 2006-08-24 | Robert Bosch Gmbh | Leaky wave antenna |
US7071888B2 (en) * | 2003-05-12 | 2006-07-04 | Hrl Laboratories, Llc | Steerable leaky wave antenna capable of both forward and backward radiation |
ATE370553T1 (en) * | 2003-08-15 | 2007-09-15 | Tdk Corp | ANTENNA SWITCHING DEVICE |
BR112013008959B1 (en) * | 2010-10-15 | 2022-01-25 | Searete Llc | ANTENNA AND METHOD FOR STANDARDIZING ELECTROMAGNETIC RADIATION BEAM |
US9455495B2 (en) * | 2010-11-03 | 2016-09-27 | The Boeing Company | Two-dimensionally electronically-steerable artificial impedance surface antenna |
US9466887B2 (en) * | 2010-11-03 | 2016-10-11 | Hrl Laboratories, Llc | Low cost, 2D, electronically-steerable, artificial-impedance-surface antenna |
US9246230B2 (en) * | 2011-02-11 | 2016-01-26 | AMI Research & Development, LLC | High performance low profile antennas |
US9385435B2 (en) * | 2013-03-15 | 2016-07-05 | The Invention Science Fund I, Llc | Surface scattering antenna improvements |
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