CN113346229A - Wide-scanning-range leaky-wave antenna based on liquid crystal tuning and implementation method thereof - Google Patents
Wide-scanning-range leaky-wave antenna based on liquid crystal tuning and implementation method thereof Download PDFInfo
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- 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
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- H01Q21/08—Arrays of individually energised antenna units similarly polarised and spaced apart the units being spaced along or adjacent to a rectilinear path
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Abstract
The invention discloses a wide scanning range leaky-wave antenna based on liquid crystal tuning and an implementation method thereof. The surface-wave-transmission-mode constant-frequency beam scanning device comprises N radiation units and a feed structure, wherein the feed structure converts electromagnetic waves into electromagnetic waves in a surface wave transmission mode, feeds the electromagnetic waves into the N radiation units, and controls the surface impedance distribution period of the N radiation units by independently controlling the voltage loaded on each radiation unit, so that constant-frequency beam scanning under the voltage control is realized; according to the invention, the beam scanning of a large-range scanning angle is obtained by controlling the modulation period, so that the antenna beam gain in the large-range beam scanning range can be kept stable, and the problem of over-small beam scanning range caused by the limited dielectric constant variation range of the liquid crystal is avoided; in addition, the liquid crystal material has the characteristic of low loss in millimeter wave and above high frequency bands, so the beam scanning antenna and the implementation method thereof provide a solution for millimeter wave mobile communication.
Description
Technical Field
The invention relates to a high-frequency communication technology, in particular to a wide-scanning-range leaky-wave antenna based on liquid crystal tuning and an implementation method thereof.
Background
The leaky-wave antenna is a traveling-wave antenna and has the advantages of low cost, low profile, high gain and the characteristic of frequency scanning, and the directional radiation angle of the high gain can be changed along with the change of the working frequency of the antenna. However, in practical communication scenarios, such frequency scanning characteristics are often not practical, and in scenarios requiring beam scanning, such as satellite communication, mobile communication, and vehicle-mounted radar, the frequency of the communication signal is a narrow-band signal with a fixed center frequency, so the fixed-frequency beam scanning characteristics are more suitable for these modern communication scenarios.
The most mature fixed frequency beam scanning mode at present is a phased array antenna, and the scanning of radiation beams is realized by adjusting the feed phase of each antenna unit, and the mode needs complex and expensive phase shifting and feed networks, and cannot be widely applied due to high cost.
The leaky-wave antenna has the beam scanning characteristic, and a dynamic element capable of changing the electromagnetic characteristic is introduced into the leaky-wave antenna, so that the low-cost fixed-frequency beam scanning antenna can be obtained. The PIN diode and the varactor diode are used as common electrically controllable dynamic elements and are applied to a fixed-frequency beam scanning leaky-wave antenna, but with the increase of communication frequency, parasitic parameters and loss of the lumped parameter elements are amplified, and the PIN diode and the varactor diode cannot be effectively applied to communication of millimeter waves with higher frequency and even terahertz wave bands.
In higher frequency communication scenarios, an alternative to highly lossy lumped parameter elements is the use of liquid crystal materials. As a uniaxial crystal, the molecular long axis orientation of the liquid crystal is deflected by an external electric field, so that the dielectric constant of the crystal is changed. The loss of the liquid crystal material is extremely low, and the liquid crystal material can be suitable for microwave, millimeter wave and terahertz wave bands, but the change range of the dielectric constant of the liquid crystal is limited, so that the scanning angle range of the fixed-frequency beam scanning leaky-wave antenna based on the liquid crystal material is extremely limited at present, and the application in modern communication scenes is greatly limited due to the narrow scanning range.
Disclosure of Invention
In order to solve the problem that the scanning range of a fixed-frequency beam scanning leaky-wave antenna based on liquid crystal tuning is small, the invention provides a wide-scanning-range leaky-wave antenna based on liquid crystal tuning and an implementation method thereof, and the wide-scanning-range leaky-wave antenna based on liquid crystal tuning has the advantages of low cost, low profile, low loss, high scanning range and the like, and has great advantages and development prospects in a millimeter wave communication system.
One object of the present invention is to provide a wide scanning range leaky-wave antenna based on liquid crystal tuning.
The invention discloses a wide scanning range leaky-wave antenna based on liquid crystal tuning, which comprises: n radiating elements and a feed structure; each radiation unit comprises a metal floor, liquid crystal, an insulating film, a radiation patch, a unit medium substrate and a metal through hole; the bottommost layer is a metal floor; the liquid crystal is an anisotropic material, the rotation angle of liquid crystal molecules influences the dielectric constant of the liquid crystal material, and the side surface of the liquid crystal is wrapped with an insulating film to expose the upper surface and the lower surface of the liquid crystal; the liquid crystal is placed on the metal floor, and the lower surface of the liquid crystal is tightly attached to the metal floor; the upper surface of the liquid crystal is provided with a radiation patch; arranging a unit medium substrate on the radiation patch, wherein the lower surface of the unit medium substrate is tightly attached to the upper surface of the radiation patch; a metal through hole vertical to the unit medium substrate is formed in the unit medium substrate, and the position of the metal through hole is right opposite to the center of the radiation patch; the metal floor and the metal through holes are respectively connected to an external direct-current voltage source through wires, so that potential difference is generated between the metal floor and the radiation patches, the rotation angle of liquid crystal molecules is controlled, and the dielectric constant of the liquid crystal material in each radiation unit is independently controlled through voltage; the plane sizes of the metal floor, the liquid crystal and the unit medium substrate are the same, namely the plane size of the radiation unit is the sub-wavelength size; the N radiating units have the same structure and the same plane size, namely the N radiating units have the same length and width; the N radiation units are arranged in a one-dimensional mode along the width direction; respectively arranging feed structures at two ends of the N radiation units which are arranged in one dimension; the feeding structures on the two sides form mirror symmetry by the plane where the midpoints of the N radiating elements are located;
electromagnetic waves are incident from a feed structure at one end, the feed structure converts the electromagnetic waves into electromagnetic waves in a surface wave transmission mode, and the electromagnetic waves are fed into the N radiation units; inputting the surface wave to the N radiating units along the one-dimensional arrangement direction of the N radiating units, namely the width direction; according to the periodic structure floriquet's theorem, when the surface impedances of the N radiating elements are periodically arranged along the surface wave transmission direction, the N radiating elements support the transmission of N-th harmonic waves of radiation in addition to the transmission of non-radiated surface waves, and the wave vector of the N-th harmonic waves is related to the period of the surface impedance distribution of the N radiating elements; when the absolute value of the wave vector of the nth harmonic wave is smaller than the absolute value of the wave vector of the free space, the electromagnetic wave is transmitted to the free space in a radiation mode, and the radiation angle is related to the wave vector of the nth harmonic wave, so that the radiation angle is controlled by regulating and controlling the period of surface impedance distribution, and the purpose of obtaining large-range wave beam scanning by controlling the period of the surface impedance distribution is achieved; and, the surface impedance of the radiating element increases with the increase of the voltage loaded on the upper and lower sides of the liquid crystal, so the period of the surface impedance distribution of the N radiating elements is controlled by independently controlling the voltage loaded on each radiating element, thereby realizing fixed frequency beam scanning under the voltage control.
The insulating film is made of polyethylene, polyvinylidene fluoride or polytetrafluoroethylene.
The shape of the radiation patch is a surface plasmon structure, and the structure has strong dispersion of surface waves, so that the surface waves can be efficiently transmitted on the structure in a long range; the radiation patch is made of metal with good conductivity, copper, aluminum or aluminum alloy.
The unit dielectric substrate is made of dielectric substrate material with low dielectric loss, such as polytetrafluoroethylene, ceramic composite material or glass fiber/epoxy resin composite material.
Corresponding to each layer of the radiating element, the feeding means comprises: the power feed floor comprises a power feed floor, a lower-layer dielectric substrate, a functional layer and an upper-layer dielectric substrate; the feed floor corresponds to the metal floor, the bottommost layer is a feed floor, and the feed floor is connected with the metal floor of the radiation unit into a whole; corresponding to the liquid crystal, a lower dielectric substrate is placed on the feed floor; arranging a functional layer on the lower medium substrate, wherein the functional layer comprises a metal strip and a metal strip, the metal strip is connected into a whole, the metal strip is engraved with a plurality of rectangular grooves with equal distances, the depth of each rectangular groove is continuously deepened towards the direction of the radiation unit, and the width of each rectangular groove is consistent with that of the metal strip; the metal strip is positioned at the outer end, and the metal strip engraved with a plurality of rectangular grooves with equal distances is positioned at one end of the radiation unit; an upper dielectric substrate is arranged on the microstrip line corresponding to the unit dielectric substrate; the feed floor, the lower dielectric substrate, the metal strip and the upper dielectric substrate form a microstrip line; the feed floor, the lower dielectric substrate, the metal strip carved with a plurality of rectangular grooves with equal distances and the upper dielectric substrate form a microstrip gradient line; and converting the guided wave mode on the microstrip line into a surface wave mode supported on the radiation unit through the microstrip gradient line.
The invention also aims to provide a method for realizing the wide-scanning-range leaky-wave antenna based on liquid crystal tuning.
The invention discloses a method for realizing a wide-scanning-range leaky-wave antenna based on liquid crystal tuning, which comprises the following steps of:
1) preparing a wide scanning range leaky-wave antenna:
a) providing a metal floor, wherein liquid crystal is an anisotropic material, the dielectric constant of the liquid crystal material is influenced by the rotation angle of liquid crystal molecules, an insulating film is wrapped on the side surface of the liquid crystal, and two end surfaces of the liquid crystal are exposed;
b) the liquid crystal wrapped by the insulating film is placed on the metal floor;
c) arranging a radiation patch on the liquid crystal wrapped by the insulating film;
d) arranging a medium substrate on the radiation patch, wherein the lower surface of the medium substrate is tightly attached to the upper surface of the radiation patch;
e) a metal through hole vertical to the medium substrate is formed in the medium substrate, and the position of the metal through hole is right opposite to the center of the radiation patch to form a radiation unit;
f) the metal floor and the metal through holes are respectively connected to an external voltage device through wires, so that potential difference is generated between the metal floor and the radiation patches, the rotation angle of liquid crystal molecules is controlled, and the dielectric constant of the liquid crystal material in each radiation unit is independently controlled through voltage;
g) arranging N radiating units in a one-dimensional mode along the width direction;
h) respectively arranging feed structures on two sides of the N radiation units which are arranged in one dimension;
2) the fundamental mode of the radiating element is a surface wave mode, and the surface impedance thereof is defined by the eigenfrequency:
wherein eta is0The wave impedance of the free space, c is the speed of light of the free space, d is the width of the radiation unit, the width direction is along the transmission direction of the surface wave, phi is the phase difference corresponding to the radiation unit in the transmission direction of the surface wave, omega is the eigen frequency of the unit, the increase of the voltage loaded on the upper side and the lower side of the liquid crystal leads to the increase of the rotation angle of the liquid crystal molecules, the increase of the rotation angle of the liquid crystal molecules leads to the increase of the equivalent dielectric constant of the liquid crystal, the increase of the equivalent dielectric constant of the liquid crystal leads to the increase of the phase difference phi, the increase of the phase difference phi leads to the increase of the surface impedance, thereby realizing that the surface impedance of the radiation unit is increased along with the increase of the voltage loaded on the upper side and the lower side of the liquid crystal;
3) electromagnetic waves are incident from a feed structure at one end, the feed structure converts the electromagnetic waves into electromagnetic waves in a surface wave transmission mode, and the electromagnetic waves are fed into the N radiation units;
4) inputting the surface wave to the N radiating units along the one-dimensional arrangement direction of the N radiating units;
5) according to the periodic structure floriquet's theorem, when the surface impedance of the radiating portion is periodically arranged along the surface wave transmission direction, the N radiating elements support the transmission of the radiated nth harmonic wave in addition to the transmission of the non-radiated surface wave, and the wave vector of the nth harmonic wave is expressed as:
wherein, beta0The wave vector of the fundamental mode is, N is the order of harmonic wave and is an integer, p is the period of the surface impedance distribution of the N radiating elements, and the formula (2) shows that the wave vector of the nth harmonic wave is related to the period of the surface impedance distribution of the N radiating elements;
6) when the absolute value of the wave vector of the nth harmonic wave is smaller than the absolute value of the wave vector of the free space, the electromagnetic wave propagates to the free space in a radiation mode, and the radiation angle is expressed as:
wherein k is0Is a wave vector of free space, and the formula (3) shows that the radiation angle is related to the wave vector of nth harmonic wave;
7) combining the formulas (2) and (3), controlling the radiation angle by regulating and controlling the period of surface impedance distribution, and realizing the purpose of obtaining large-range beam scanning by controlling the period of surface impedance distribution;
8) and, the surface impedance of the radiating element increases with the increase of the voltage loaded on the upper and lower sides of the liquid crystal, so the period of the surface impedance distribution of the N radiating elements is controlled by independently controlling the voltage loaded on each radiating element, thereby realizing fixed frequency beam scanning under the voltage control.
Further, the target radiation range of the wide scanning range leaky-wave antenna is thetamin～θmaxWhen theta is greater than thetaminAs minimum value of the angle of radiation, thetamaxThe period p of the surface impedance distribution obtained by combining the formulas (2) and (3) is obtained by sampling a sine curve, the period of the sine curve is recorded as the period of the impedance distribution,the range over which the beam sweep is continuous, and thus continuously tuned, should be:
since a continuous impedance distribution cannot be obtained because of the interval of the width d of the radiating elements between the elements, the impedance distribution is discretized, and the voltage control is performed on the elements by using the impedance at the center position of each element by using a sampling method.
The invention has the advantages that:
according to the invention, the beam scanning of a large-range scanning angle is obtained by controlling the modulation period, so that the antenna beam gain in the large-range beam scanning range can be kept stable, and the problem of over-small beam scanning range caused by the limited dielectric constant variation range of the liquid crystal is avoided; in addition, the liquid crystal material has the characteristic of low loss in millimeter wave and above high frequency bands, so the beam scanning antenna and the implementation method thereof provide a solution for millimeter wave mobile communication.
Drawings
FIG. 1 is a schematic diagram of one embodiment of a wide scan range leaky-wave antenna based on liquid crystal tuning of the present invention;
FIG. 2 is a schematic diagram of a radiating element of one embodiment of a liquid crystal tuning based wide scan range leaky-wave antenna of the present invention;
FIG. 3 is a schematic diagram of a feed structure of one embodiment of a liquid crystal tuning based wide scan range leaky-wave antenna of the invention;
FIG. 4 is a graph of the surface impedance of a radiating element obtained by one embodiment of a wide scan range leaky-wave antenna based on liquid crystal tuning of the present invention;
FIG. 5 is a graph of the periodic variation of the main radiation lobe angle with the surface impedance distribution, obtained by an embodiment of the wide scanning range leaky-wave antenna based on liquid crystal tuning according to the invention;
fig. 6 is a scanned beam pattern obtained by one embodiment of the wide scanning range leaky-wave antenna based on liquid crystal tuning of the invention.
Detailed Description
The invention will be further elucidated by means of specific embodiments in the following with reference to the drawing.
As shown in fig. 1, the wide scanning range leaky-wave antenna based on liquid crystal tuning of the present invention in this embodiment includes: n radiating elements and a feed structure; as shown in fig. 2, each radiation unit includes a metal floor 106, a liquid crystal 105, an insulating film 104, a radiation patch 102, a unit dielectric substrate 101, and a metal via hole 103; wherein, the bottommost layer is a metal floor 106; the liquid crystal is an anisotropic material, the rotation angle of liquid crystal molecules influences the dielectric constant of the liquid crystal material, and the side surface of the liquid crystal is wrapped with an insulating film 104 to expose the upper surface and the lower surface of the liquid crystal; the liquid crystal is placed on the metal floor 106, and the lower surface of the liquid crystal is tightly attached to the metal floor 106; the upper surface of the liquid crystal is provided with a radiation patch 102; a unit medium substrate 101 is arranged on the radiation patch 102, and the lower surface of the unit medium substrate 101 is tightly attached to the upper surface of the radiation patch 102; a metal through hole 103 vertical to the unit medium substrate 101 is formed in the unit medium substrate 101, and the position of the metal through hole 103 is opposite to the center of the radiation patch 102; the metal floor 106 and the metal through holes 103 are respectively connected to an external direct current voltage source through wires, the whole metal floor 106 is connected with 0 voltage, and each unit is independently applied with independent voltage above the unit, so that a potential difference is generated between the metal floor 106 and the radiation patches 102, the rotation angle of liquid crystal molecules is controlled, and the dielectric constant of a liquid crystal material in each radiation unit is independently controlled through the voltage; the plane dimensions of the metal floor 106, the liquid crystal and the unit dielectric substrate 101 are all the same, that is, the plane dimension of the radiation unit is a sub-wavelength dimension; the N radiating units have the same structure and the same plane size, namely the N radiating units have the same length and width; the N radiation units are arranged in a one-dimensional mode along the width direction; respectively arranging feed structures at two ends of the N radiation units which are arranged in one dimension; the feeding structures on the two sides form mirror symmetry with the plane where the midpoints of the N radiating elements are located.
As shown in fig. 3, the feeding device includes a feeding floor 205, a lower dielectric substrate 203, a functional layer, and an upper dielectric substrate 204, corresponding to each layer of the radiating element; wherein, corresponding to the metal floor 106, the bottom layer is a feed floor 205, and the feed floor 205 is connected with the metal floor 106 of the radiation unit into a whole; corresponding to the liquid crystal, a lower dielectric substrate 203 is placed on the feed floor 205; a functional layer is arranged on a lower medium substrate 203, the functional layer comprises a metal strip 201 and a metal strip 202 engraved with a plurality of rectangular grooves with equal distances, the depth of each rectangular groove is continuously deepened towards the direction of the radiation unit, and the width of each rectangular groove is consistent with that of the metal strip; the metal strip is positioned at the outer end, and the metal strip engraved with a plurality of rectangular grooves with equal distances is positioned at one end of the radiation unit; an upper dielectric substrate 204 is arranged on the microstrip line corresponding to the unit dielectric substrate 101; the feed floor 205, the lower dielectric substrate 203, the metal strip and the upper dielectric substrate 204 form a microstrip line; the feed floor 205, the lower dielectric substrate 203, the metal strip carved with a plurality of rectangular grooves with equal distances and the upper dielectric substrate 204 form a microstrip gradient line; an upper dielectric substrate 204 on the unit dielectric substrate 101; and converting the guided wave mode on the microstrip line into a surface wave mode supported on the sub-wavelength size unit through the microstrip gradient line.
In the present embodiment, the material of the insulating film 104 is polyethylene; the radiation patch 102 has a longitudinal patch and a transverse patch, wherein the two longitudinal patches are parallel to each other along the length direction of the radiation unit, and are connected to each other by the transverse patch, and the whole width is a11mm, overall length a21.5mm, width of the longitudinal patch w10.3mm, width of the transverse patch w20.3 mm; the thickness t of the insulating film 104 is 0.1mm, the height h of the liquid crystal is 1mm, the width d of the radiating unit is 1.5mm, and the radiating patch 102 of the metal through hole 103 is made of copper; the dielectric substrate having a dielectric constant of 2.2, a loss tangent of 0.003 and a thickness h was used as the material for the unit dielectric substrate 101t0.5 mm. The liquid crystal was of type GT3-24001, the relative dielectric constant in the major axis direction of the liquid crystal molecules was 3.3, the relative dielectric constant in the minor axis direction of the liquid crystal molecules was 2.5, the rotation angle of the liquid crystal molecules varied with the voltage, resulting in the variation of the surface impedance of the cell, FIG. 4 shows the liquid crystal moleculesThe relationship between the rotation angle of the seed and the cell surface impedance. In order to ensure the matching between the feed source and the radiation structure and reduce the return loss of the input end, the feed structure adopts a gradual change microstrip line structure. The working frequency is 30 GHz; when the target radiation angle is continuously scanned from-60 degrees to +60 degrees, the surface impedance period of the antenna radiation structure obtained by the formulas (2) and (3) is continuously changed from 3.1d to 16.7 d. The angle of the main radiation lobe of the antenna under different period modulations is shown in fig. 5, and the angle of the main radiation lobe of the antenna increases with the increase of the modulation period. In fig. 6, the directional patterns of the antenna under different periodic modulations are shown, the main lobe direction of the antenna gradually scans along with the change of the modulation period, and stable gain is kept in a large scanning range.
The implementation method of the wide scanning range leaky-wave antenna based on liquid crystal tuning in the embodiment comprises the following steps:
1) preparing a wide scanning range leaky-wave antenna:
a) providing a metal floor 106, wherein liquid crystal is an anisotropic material, the dielectric constant of the liquid crystal material is influenced by the rotation angle of liquid crystal molecules, an insulating film 104 is wrapped on the side surface of the liquid crystal, and two end surfaces of the liquid crystal are exposed;
b) the liquid crystal wrapped with the insulating film 104 is placed on the metal floor 106;
c) a radiation patch 102 is provided on a liquid crystal wrapped with an insulating film 104;
d) a dielectric substrate is arranged on the radiation patch 102, and the lower surface of the dielectric substrate is tightly attached to the upper surface of the radiation patch 102;
e) a metal through hole 103 perpendicular to the dielectric substrate is formed in the dielectric substrate, and the position of the metal through hole 103 is opposite to the center of the radiation patch 102 to form a radiation unit;
f) the metal floor 106 and the metal through hole 103 are respectively connected to an external voltage device through wires, so that a potential difference is generated between the metal floor 106 and the radiation patch 102, thereby controlling the rotation angle of liquid crystal molecules, and further independently controlling the dielectric constant of the liquid crystal material in each radiation unit through voltage;
g) arranging N radiating units in a one-dimensional mode along the width direction;
h) respectively arranging feed structures on two sides of the N radiation units which are arranged in one dimension;
2) the fundamental mode of the radiating element is a surface wave mode, and the surface impedance thereof is defined by the eigenfrequency:
wherein eta is0The wave impedance of the free space, c is the speed of light of the free space, d is the width of the radiation unit, the width direction is along the transmission direction of the surface wave, phi is the phase difference corresponding to the radiation unit in the transmission direction of the surface wave, omega is the eigen frequency of the unit, the increase of the voltage loaded on the upper side and the lower side of the liquid crystal leads to the increase of the rotation angle of the liquid crystal molecules, the increase of the rotation angle of the liquid crystal molecules leads to the increase of the equivalent dielectric constant of the liquid crystal, the increase of the equivalent dielectric constant of the liquid crystal leads to the increase of the phase difference phi, the increase of the phase difference phi leads to the increase of the surface impedance, thereby realizing that the surface impedance of the radiation unit is increased along with the increase of the voltage loaded on the upper side and the lower side of the liquid crystal;
3) electromagnetic waves are incident from a feed structure at one end, the feed structure converts the electromagnetic waves into electromagnetic waves in a surface wave transmission mode, and the electromagnetic waves are fed into the N radiation units;
4) inputting the surface wave to the N radiating units along the one-dimensional arrangement direction of the N radiating units;
5) according to the periodic structure floriquet's theorem, when the surface impedance of the radiating portion is periodically arranged along the surface wave transmission direction, the N radiating elements support the transmission of the radiated nth harmonic wave in addition to the transmission of the non-radiated surface wave, and the wave vector of the nth harmonic wave is expressed as:
wherein, beta0Is the wave vector of the fundamental mode, N is the order of harmonic wave, an integer, p is the period of the surface impedance distribution of N radiating elements, and (2) formula shows the wave vector of N-th harmonic wave and N radiationThe periodicity of the surface impedance distribution of the cell is related;
6) when the absolute value of the wave vector of the nth harmonic wave is smaller than the absolute value of the wave vector of the free space, the electromagnetic wave propagates to the free space in a radiation mode, and the radiation angle is expressed as:
wherein k is0Is a wave vector of free space, and the formula (3) shows that the radiation angle is related to the wave vector of nth harmonic wave;
7) combining the formulas (2) and (3), controlling the radiation angle by regulating the period of surface impedance distribution, and obtaining large-range beam scanning by controlling the period of surface impedance distribution;
8) and, the surface impedance of the radiating element increases with the increase of the voltage loaded on the upper and lower sides of the liquid crystal, so the period of the surface impedance distribution of the N radiating elements is controlled by independently controlling the voltage loaded on each radiating element, thereby realizing fixed frequency beam scanning under the voltage control.
Further, the target radiation range of the wide scanning range leaky-wave antenna is thetamin～θmaxWhen theta is greater than thetaminAs minimum value of the angle of radiation, thetamaxFor the maximum value of the radiation angle, the period p of the surface impedance distribution obtained by combining the formulas (2) and (3) is obtained by sampling a sine curve, the period of the sine curve is recorded as the period of the impedance distribution, so that the continuously tuned period distribution is obtained, and the range of the beam scanning which is continuous is obtained by adopting the formula
Since a continuous impedance distribution cannot be obtained due to the interval of d between cells, the impedance distribution is discretized and the cells are voltage-controlled by the impedance at the center of each cell using a sampling method.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.
Claims (7)
1. A wide scanning range leaky-wave antenna based on liquid crystal tuning is characterized in that the wide scanning range leaky-wave antenna based on liquid crystal tuning comprises: n radiating elements and a feed structure; each radiation unit comprises a metal floor, liquid crystal, an insulating film, a radiation patch, a unit medium substrate and a metal through hole; the bottommost layer is a metal floor; the liquid crystal is an anisotropic material, the rotation angle of liquid crystal molecules influences the dielectric constant of the liquid crystal material, and the side surface of the liquid crystal is wrapped with an insulating film to expose the upper surface and the lower surface of the liquid crystal; the liquid crystal is placed on the metal floor, and the lower surface of the liquid crystal is tightly attached to the metal floor; the upper surface of the liquid crystal is provided with a radiation patch; arranging a unit medium substrate on the radiation patch, wherein the lower surface of the unit medium substrate is tightly attached to the upper surface of the radiation patch; a metal through hole vertical to the unit medium substrate is formed in the unit medium substrate, and the position of the metal through hole is right opposite to the center of the radiation patch; the metal floor and the metal through holes are respectively connected to an external direct-current voltage source through wires, so that potential difference is generated between the metal floor and the radiation patches, the rotation angle of liquid crystal molecules is controlled, and the dielectric constant of the liquid crystal material in each radiation unit is independently controlled through voltage; the plane sizes of the metal floor, the liquid crystal and the unit medium substrate are the same, namely the plane size of the radiation unit is the sub-wavelength size; the N radiating units have the same structure and the same plane size, namely the N radiating units have the same length and width; the N radiation units are arranged in a one-dimensional mode along the width direction; respectively arranging feed structures at two ends of the N radiation units which are arranged in one dimension; the feeding structures on the two sides form mirror symmetry by the plane where the midpoints of the N radiating elements are located;
electromagnetic waves are incident from a feed structure at one end, the feed structure converts the electromagnetic waves into electromagnetic waves in a surface wave transmission mode, and the electromagnetic waves are fed into the N radiation units; inputting the surface wave to the N radiating units along the one-dimensional arrangement direction of the N radiating units; according to the ferouq theorem of the periodic structure, when the surface impedances of the N radiating elements are periodically arranged along the surface wave transmission direction, the N radiating elements support the transmission of N-th harmonic waves of radiation besides the transmission of non-radiated surface waves, and the wave vector of the N-th harmonic waves is related to the period of the surface impedance distribution of the N radiating elements; when the absolute value of the wave vector of the nth harmonic wave is smaller than the absolute value of the wave vector of the free space, the electromagnetic wave is transmitted to the free space in a radiation mode, and the radiation angle is related to the wave vector of the nth harmonic wave, so that the radiation angle is controlled by regulating and controlling the period of surface impedance distribution, and the purpose of obtaining large-range wave beam scanning by controlling the period of the surface impedance distribution is achieved; and, the surface impedance of the radiating element increases with the increase of the voltage loaded on the upper and lower sides of the liquid crystal, so the period of the surface impedance distribution of the N radiating elements is controlled by independently controlling the voltage loaded on each radiating element, thereby realizing fixed frequency beam scanning under the voltage control.
2. The liquid crystal tuning-based wide scan range leaky-wave antenna as claimed in claim 1, wherein a material of said insulating film is polyethylene, polyvinylidene fluoride, or polytetrafluoroethylene.
3. The liquid crystal tuning based wide scan range leaky-wave antenna as claimed in claim 1, wherein said radiating patch is shaped as a surface plasmon structure.
4. The liquid crystal tuning-based wide-scanning-range leaky-wave antenna as claimed in claim 1, wherein the material of said unit dielectric substrate is a dielectric substrate material with low dielectric loss.
5. The wide scanning range leaky-wave antenna based on liquid crystal tuning as claimed in claim 1, wherein said feeding means includes, in correspondence with each layer of the radiation element: the power feed floor comprises a power feed floor, a lower-layer dielectric substrate, a functional layer and an upper-layer dielectric substrate; the feed floor corresponds to the metal floor, the bottommost layer is a feed floor, and the feed floor is connected with the metal floor of the radiation unit into a whole; corresponding to the liquid crystal, a lower dielectric substrate is placed on the feed floor; arranging a functional layer on the lower medium substrate, wherein the functional layer comprises a metal strip and a metal strip, the metal strip is connected into a whole, the metal strip is engraved with a plurality of rectangular grooves with equal distances, the depth of each rectangular groove is continuously deepened towards the direction of the radiation unit, and the width of each rectangular groove is consistent with that of the metal strip; the metal strip is positioned at the outer end, and the metal strip engraved with a plurality of rectangular grooves with equal distances is positioned at one end of the radiation unit; an upper dielectric substrate is arranged on the microstrip line corresponding to the unit dielectric substrate; the feed floor, the lower dielectric substrate, the metal strip and the upper dielectric substrate form a microstrip line; the feed floor, the lower dielectric substrate, the metal strip carved with a plurality of rectangular grooves with equal distances and the upper dielectric substrate form a microstrip gradient line; and converting the guided wave mode on the microstrip line into a surface wave mode supported on the radiation unit through the microstrip gradient line.
6. The implementation method of the wide scanning range leaky-wave antenna based on liquid crystal tuning as claimed in claim 1, wherein the implementation method comprises the following steps:
1) preparing a wide scanning range leaky-wave antenna:
a) providing a metal floor, wherein liquid crystal is an anisotropic material, the dielectric constant of the liquid crystal material is influenced by the rotation angle of liquid crystal molecules, an insulating film is wrapped on the side surface of the liquid crystal, and two end surfaces of the liquid crystal are exposed;
b) the liquid crystal wrapped by the insulating film is placed on the metal floor;
c) arranging a radiation patch on the liquid crystal wrapped by the insulating film;
d) arranging a medium substrate on the radiation patch, wherein the lower surface of the medium substrate is tightly attached to the upper surface of the radiation patch;
e) a metal through hole vertical to the medium substrate is formed in the medium substrate, and the position of the metal through hole is right opposite to the center of the radiation patch to form a radiation unit;
f) the metal floor and the metal through holes are respectively connected to an external voltage device through wires, so that potential difference is generated between the metal floor and the radiation patches, the rotation angle of liquid crystal molecules is controlled, and the dielectric constant of the liquid crystal material in each radiation unit is independently controlled through voltage;
g) arranging N radiating units in a one-dimensional mode along the width direction;
h) respectively arranging feed structures on two sides of the N radiation units which are arranged in one dimension;
2) the fundamental mode of the radiating element is a surface wave mode, and the surface impedance thereof is defined by the eigenfrequency:
wherein eta is0The wave impedance of the free space, c is the speed of light of the free space, d is the width of the radiation unit, the width direction is along the transmission direction of the surface wave, phi is the phase difference corresponding to the radiation unit in the transmission direction of the surface wave, omega is the eigen frequency of the unit, the increase of the voltage loaded on the upper side and the lower side of the liquid crystal leads to the increase of the rotation angle of the liquid crystal molecules, the increase of the rotation angle of the liquid crystal molecules leads to the increase of the equivalent dielectric constant of the liquid crystal, the increase of the equivalent dielectric constant of the liquid crystal leads to the increase of the phase difference phi, the increase of the phase difference phi leads to the increase of the surface impedance, thereby realizing that the surface impedance of the radiation unit is increased along with the increase of the voltage loaded on the upper side and the lower side of the liquid crystal;
3) electromagnetic waves are incident from a feed structure at one end, the feed structure converts the electromagnetic waves into electromagnetic waves in a surface wave transmission mode, and the electromagnetic waves are fed into the N radiation units;
4) inputting the surface wave to the N radiating units along the one-dimensional arrangement direction of the N radiating units;
5) according to the theory of the periodic structure of feroquin, when the surface impedance of the radiating portion is periodically arranged along the transmission direction of the surface wave, the N radiating elements support the transmission of N harmonics of the radiation in addition to the transmission of the non-radiated surface wave, and the wave vector of the N harmonics is expressed as:
wherein, beta0The wavevector of the fundamental mode, N is the order of harmonic, p is the period of the surface impedance distribution of the N radiating elements, and the formula (2) shows that the wavevector of the nth harmonic is related to the period of the surface impedance distribution of the N radiating elements;
6) when the absolute value of the wave vector of the nth harmonic wave is smaller than the absolute value of the wave vector of the free space, the electromagnetic wave is transmitted to the free space in a radiation mode, and the radiation angle is expressed as:
wherein k is0Is a wave vector of free space, and the formula (3) shows that the radiation angle is related to the wave vector of nth harmonic wave;
7) combining the formulas (2) and (3), controlling the radiation angle by regulating and controlling the period of surface impedance distribution, and realizing the purpose of obtaining large-range beam scanning by controlling the period of surface impedance distribution;
8) and, the surface impedance of the radiating element increases with the increase of the voltage loaded on the upper and lower sides of the liquid crystal, so the period of the surface impedance distribution of the N radiating elements is controlled by independently controlling the voltage loaded on each radiating element, thereby realizing fixed frequency beam scanning under the voltage control.
7. The implementation of claim 6 wherein the target radiation range of the wide scan range leaky-wave antenna is θmin～θmaxWhen theta is greater than thetaminAs minimum value of the angle of radiation, thetamaxFor the maximum value of the radiation angle, the period p of the surface impedance distribution obtained by combining the formulas (2) and (3) is obtained by sampling a sine curve, and the period of the sine curve is recorded as the impedance distribution period, so as to obtain a continuously tuned period distribution, so that the range of obtaining the beam scanning as continuous should be:
since a continuous impedance distribution cannot be obtained because of the interval of the width d of the radiating elements between the elements, the impedance distribution is discretized, and the voltage control is performed on the elements by using the impedance at the center position of each element by using a sampling method.
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