WO2018220407A1

WO2018220407A1 - Reconfigurable half-width leaky-wave antenna

Info

Publication number: WO2018220407A1
Application number: PCT/GB2018/051523
Authority: WO
Inventors: Sampson HU; Farshad ESHGHABADI; Liang Wan
Original assignee: Smart Antenna Technologies Ltd
Priority date: 2017-06-02
Filing date: 2018-06-04
Publication date: 2018-12-06
Also published as: GB201708811D0

Abstract

There is disclosed a reconfigurable, leaky-wave antenna device comprising: a groundplane; a septum extending substantially perpendicularly from the groundplane and extending along a length thereof; a first main microstrip transmission line having first and second opposed lengthwise edges, the first edge connected to the septum, the first main microstrip transmission line extending substantially parallel to and above the groundplane to one side of the septum; and a first subsidiary microstrip transmission line, arranged alongside the second edge of the first main microstrip transmission line. The first main and first subsidiary microstrip transmission lines are connected to each other at a plurality of points along their respective lengths by reconfigurable electronic components.

Description

RECONFIGURABLE HALF-WIDTH LEAKY-WAVE ANTENNA

[0001] This invention relates to a half-width leaky-wave antenna, using reconfigurable elements and shape in order to control various properties of the emitted radiation to assist with beam-forming and other telecommunications techniques.

BACKGROUND

[0002] In the context of the present application, a "balanced antenna" is an antenna that has a pair of radiating arms extending in different, for example opposed or orthogonal, directions away from a central feed point. Examples of balanced antennas include dipole antennas and loop antennas. In a balanced antenna, the radiating arms are fed against each other, and not against a groundplane. In many balanced antennas, the two radiating arms are substantially symmetrical with respect to each other, although some balanced antennas may have one arm that is longer, wider or otherwise differently configured to the other arm. A balanced antenna is usually fed by way of a balanced feed.

[0003] In contrast, an "unbalanced antenna" is an antenna that is fed against a groundplane, which serves as a counterpoise. An unbalanced antenna may take the form of a monopole antenna fed at one end, or may be configured as a centre fed monopole or otherwise. An unbalanced antenna may be configured as a chassis antenna, in which the antenna generates currents in the chassis of the device to which the antenna is attached, typically a groundplane of the device. The currents generated in the chassis or groundplane give rise to radiation patterns that participate in the transmission/reception of RF signals. An unbalanced antenna is usually fed by way of an unbalanced feed.

[0004] A balun may be used to convert a balanced feed to an unbalanced feed and vice versa.

[0005] A reconfigurable antenna is an antenna capable of modifying dynamically its frequency and radiation properties in a controlled and reversible manner. In order to provide a dynamical response, reconfigurable antennas integrate an inner mechanism (such as RF switches, varactors, mechanical actuators or tuneable materials) that enable the intentional redistribution of the RF currents over the antenna surface and produce reversible modifications over its properties. Reconfigurable antennas differ from smart antennas because the reconfiguration mechanism lies inside the antenna rather than in an external beamforming network. The reconfiguration capability of reconfigurable antennas is used to maximize the antenna performance in a changing scenario or to satisfy changing operating requirements. [0006] Fifth generation mobile telecommunication and data services (5G) are promising to provide higher capacities, support more users simultaneously and provide higher data throughput than current 4G LTE based solutions. This next generation communication standard uses much higher frequencies, with the US Federal Communications Commission (FCC) having already approved spectrum in 28GHz, 37GHz and 39GHz bands.

[0007] As the standards for 5G evolve, it is becoming clear that beam-forming or beam- steering will be a major component in negating interference and allowing throughput to simultaneous users in close proximity. Beam-forming is the steering of the radiation pattern of the source node to direct the majority of the relevant communication to the user receiving node.

[0008] There are a number of techniques that can be used to beam-form, the first being mechanical rotation of the radome such as in air-traffic control and marine radars. However, one of the most popular techniques is to use an array of antennas that are driven with a phase difference, in order to create constructive and destructive interference in the wavefront, therefore creating a directed front to the user. Phased arrays are inherently complex and require special control hardware and software in order to create the active beam-steering effect and as such, along with mechanical solutions, would be too bulk and power hungry for mobile devices such as laptops, tablets or mobile phones using 5G services.

[0009] Another technique to beam-steer is to use the properties of the antenna radiation pattern in conjunction with reconfigurable components. Leaky-wave antennas lend themselves well to such techniques. Conventional leaky wave antennas differ from resonant antennas in that radiation emanates from a travelling wave across the conductor. Leaky-wave or fast-wave type antennas propagate surface travelling waves faster than the speed of light in the free-space; resulting in continuous radiation along the length. This type of radiating mode forms highly directed beams with small side-lobes, at angles controlled by the phase constant. The phase constant changes with the frequency and therefore in conventional mode, the beam angle is frequency-dependent.

[0010] The properties of leaky-wave antennas, plus other advantages such as very low insertion loss, compact form-factor and are cheaper than arrays, mean they are a good candidate for enabling beam-steering in compact or portable devices.

[0011] Beam-steering using leaky-wave antennas is known in the art, for example Menzel published papers in the late 1970s describing full-width microstrip leaky wave antennas. These antennas had a compact footprint and the angle of the beam could be changed from end fire 90 degrees to normal 0 degrees. However, this antenna structure required numerous evolutions, such as a centre-line grounding wall, as well as transverse slots cut in the stripline, to get it to radiate correctly.

[0012] Further development of this concept is detailed in a paper by Thiele and Zelinski entitled: Half width leaky wave antennas, and patent US7109928B1 by Thiele. These further improvements change the T-shaped full-width antenna to a half-width shape (see Figure 1). The half-width design radiates correctly, suppressing the unwanted fundamental transmission mode, to allow radiating modes, without requiring the transverse slots and improved radiation efficiency.

[0013] A further example of improvements made to the leaky wave antenna can be found in US8836594B2 by Rothwell, which describes a derivative of the Thiele design which uses capacitors along the length of the stripline to switch in and change the effective electrical width, which modifies the beam angle for a fixed frequency. However, in this arrangement (see Figure 2), the switched components form the grounded plane, as all capacitors are switched to ground when operated.

[0014] The range of the beam sweep can be extended, as described in US20140300520A1 by Nguyen et al., by simply switching the feed ends of the device. Using a switched feed enables a full 180 degrees (-90:0:90) sweep of the space above the leaky-wave antenna (see Figure 3).

[0015] While these further examples may enable enhanced beam steering, they do themselves have some drawbacks.

[0016] Switching the electrical width of the stripline to ground can have significant effects on the radiation mode, and therefore can affect efficiencies. This is due the antenna being changed into a transmission line and simply transferring the signal to the load without radiating. In the case of Rothwell, the steering angle range is limited to around 25 degrees because increasing capacitances cause degradation of the input return loss. As a result of the input return loss degradation during beam steering, the radiated power decreases as the antenna is further reconfigured, meaning that at certain angles the power becomes unusable and therefore limits the useful range of the beam steering.

[0017] It would therefore be desirable to overcome the aforementioned problems in microstrip half-width leaky wave antennas in order to increase efficiencies and extend the useful range of the beam steering effect whilst maintaining useful radiated output power. BRIEF SUMMARY OF THE DISCLOSURE

[0018] Embodiments of the present disclosure provide a stripline reconfigurable half- width leaky-wave (HW-LWA) antenna using multiple reconfigurable components along the length, that change the effective electrical width of the stripline without switching to ground. A further embodiment enhances the steering range and maintaining output power by using two parallel back-to-back arranged half-width antennas with different septum heights (ground stub heights) and sharing a common ground. A further embodiment uses multiple reconfigurable components arranged along the septum (ground-stub) to change the effective height in multiple places along the length of the stripline. Another embodiment uses the arrangement to produce two independent and simultaneously controlled beams of the same frequency. Another embodiment operates the arrangement at two separate frequency bands using different widths of stripline on each antenna.

[0019] Embodiments of the present disclosure make use of reconfiguration switches in circuit rather than to ground. This does not affect the radiation modes and helps to maintain efficiency.

[0020] Embodiments of the present disclosure may employ multi-height substrates to allow enhanced sweep radiation power.

[0021] In some embodiments, the shape of the antenna may be configured to allow control of polarisation.

[0022] Some embodiments may provide enhanced useful beam sweep with usable radiation power over an extended area compared with previous solutions.

[0023] Some embodiments may support control of two beams simultaneously.

[0024] Some embodiments may support dual bands simultaneously.

[0025] Some embodiments may provide control over properties such as polarisation and beam-shape, in addition to direction.

[0026] Viewed from a first aspect, there is provided a reconfigurable, leaky-wave antenna device comprising:

a groundplane;

a septum extending substantially perpendicularly from the groundplane and extending along a length thereof;

a first main microstrip transmission line having first and second opposed lengthwise edges, the first edge connected to the septum, the first main microstrip transmission line extending substantially parallel to and above the groundplane to one side of the septum; and a first subsidiary microstrip transmission line, arranged alongside the second edge of the first main microstrip transmission line;

wherein the first main and first subsidiary microstrip transmission lines are connected to each other at a plurality of points along their respective lengths by reconfigurable electronic components.

[0027] The antenna device may further comprise:

a second main microstrip transmission line having first and second opposed lengthwise edges, the first edge connected to the septum, the second main microstrip transmission line extending substantially parallel to and above the groundplane to the other side of the septum from the first main microstrip transmission line; and

a second subsidiary microstrip transmission line, arranged alongside the second edge of the second main microstrip transmission line;

wherein the second main and second subsidiary microstrip transmission lines are connected to each other at a plurality of points along their respective lengths by reconfigurable electronic components.

[0028] The first main and the first subsidiary microstrip transmission lines may be spaced from the groundplane by a first distance and the second main and second subsidiary microstrip transmission lines may be spaced from the groundplane by a second distance different from the first distance.

[0029] The first main and the first subsidiary microstrip transmission lines may be disposed in a first plane and the second main and second subsidiary microstrip transmission lines may be disposed in a second plane different from the first plane. In this embodiment, the first and second main microstrip transmission lines are stepped or offset relative to each other on either side of the septum.

[0030] Alternatively, the first and second main and subsidiary microstrip transmission lines may all be disposed in the same plane, and the groundplane on one side of the septum may be elevated relative to the groundplane on the other side of the septum. This may be done, for example, by way of an additional conductive layer connected to and disposed above the main groundplane on one side of the septum, or by way of an array of conductive pins or vias extending from the groundplane towards the microstrip transmission line on one side of the septum.

[0031] The first and second main microstrip transmission lines may be of different widths, or may have the same width as each other.

[0032] The reconfigurable electronic components may be selected from the group consisting of: varactors, impedance networks, non-Foster elements, tuneable capacitors, and RF switches. In some embodiments, the electronic components may comprise a simple linear arrangement of switches between the respective main and subsidiary microstrip transmission lines.

[0033] There may be provided a first antenna device of the first aspect, in combination with a second antenna device of the first aspect, wherein the antenna devices are arranged parallel to each other and wherein the first antenna device is fed from one end to allow beam steering in a range from -90° to 0° relative to a normal to the antenna devices, and wherein the second antenna device is fed from an opposite end to allow beam steering in a range from 0° to 90° relative to the normal to the antenna devices. The first and second antennas may be colinear, or may be coterminous, or may be arranged in other parallel arrangements.

[0034] Viewed from a second aspect, there is provided a reconfigurable, leaky-wave antenna device comprising:

a groundplane;

a first microstrip transmission line having first and second opposed lengthwise edges, the first edge connected to the septum, the first microstrip transmission line extending substantially parallel to and above the groundplane to one side of the septum; and

a second microstrip transmission having first and second opposed lengthwise edges, the first edge connected to the septum, the second microstrip transmission line extending substantially parallel to and above the groundplane to the other side of the septum from the first main microstrip transmission line;

wherein the first microstrip transmission line is spaced from the groundplane by a first distance and the second microstrip transmission line is spaced from the groundplane by a second distance different from the first distance; and

wherein the first and second microstrip transmission lines are connected to ground at a plurality of points along their respective lengths by switchable electronic components.

[0035] The first microstrip transmission line may be disposed in a first plane and the second microstrip transmission line may be disposed in a second plane different from the first plane.

[0036] Alternatively, the first and second microstrip transmission lines may be disposed in the same plane, and the groundplane on one side of the septum may be elevated relative to the groundplane on the other side of the septum. [0037] The first and second microstrip transmission lines may be of different widths, or may be of the same width.

[0038] The electronic components may be selected from the group consisting of: varactors, impedance networks, non-Foster elements, tuneable capacitors, and RF switches. In some embodiments, the electronic components may comprise a simple linear arrangement of switches between the respective microstrip transmission line and the groundplane.

[0039] The septum and the microstrip transmission lines may follow a substantially straight path.

[0040] Alternatively, the septum and the microstrip transmission lines may follow a curved path.

[0041] In some embodiments, the septum and the microstrip transmission lines may follow a serpentine path. In these embodiments, the antenna device may comprise a linear array of septum and microstrip subunits, each subtending an arc of substantially 90° or of substantially 180°, the subunits being arranged such that the linear array follows the serpentine path. An arc of substantially 90° may have a length of substantially one quarter of a wavelength of operation. An arc of substantially 180° may have a length of substantially one half of a wavelength of operation.

[0042] The main microstrip transmission line of the first aspect may be curled across its width, with the groundplane correspondingly curled to maintain a substantially constant separation distance from the main microstrip transmission line.

[0043] The first and/or second microstrip transmission line of the second aspect may be curled across its width, with the groundplane correspondingly curled to maintain a substantially constant separation distance from the respective first and/or second microstrip transmission line.

[0044] The groundplane and respective microstrip transmission line may be curled to form a full or partial tube structure.

[0045] The septum may be formed from at least one of: solid metal, metal foil, and a linear array of conductive pins or vias connecting the groundplane to the respective main or first or second microstrip transmission line.

[0046] The antenna device may further comprise a control processor to control the electronic components. [0047] The control processor may be operable to steer an angle of a beam radiated by the antenna device. The angle of the beam may be steerable, in relation to a normal, between broadside (0°) and endfire (±90°) directions.

[0048] The control processor may be operable to change an effective electrical width of the respective microstrip transmission line by switching in or out one or more of the electronic components.

[0049] The control processor may be operable to change an effective electrical length of the respective microstrip transmission line by switching in or out one or more of the electronic components.

[0050] The control processor may be operable to switch a feed from one microstrip transmission line to another, and/or to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line.

[0051] The control processor may be operable to detect an efficiency of the antenna device, and to reconfigure the electronic components and/or the feeding of the microstrip transmission line(s) in order to maintain efficiency.

[0052] The control processor may be operable to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line so as to change a circular polarisation property of a radiated beam.

[0053] The control processor may be operable to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line so as to invert an angle of a radiated beam relative to broadside.

[0054] The antenna device may be implemented on a multilayer PCB, for example on FR4 or Duroid®.

[0055] The antenna device may be configured for beam-forming or MIMO operation.

[0056] The length of the antenna device (that is, the length of the septum and the associated microstrip transmission lines) in the straight embodiments may be a multiple of the wavelength λο at the operating frequency, known as a unit cell. In the serpentine embodiments, the length may be configured to be multiples of half or quarter wavelength unit cells.

[0057] In an ideal scenario, an infinitely long antenna has a perfect beam in one direction. However, in reality, the finite size of the antenna almost always means that there is a reflected component in the opposite direction, either causing a second minor beam, or degrading the main beam. Therefore, the optimum length of the final arrangement is a compromise of the space constraints and the beam quality required by the specific solution for which the antenna is designed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] For a better understanding of the present invention, and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying drawings, in which:

Figure 1 shows three different prior art leaky-wave antennas in schematic form;

Figure 2 shows a further prior art leaky-wave antenna in schematic form;

Figure 3 shows another prior art leaky-wave antenna being used for beam-steering;

Figure 4 shows a plan view of a first embodiment in schematic form;

Figures 5a and 5b show a cross-sectional and perspective view of a first variation of the first embodiment in schematic form;

Figures 5c and 5d show a cross-sectional and perspective view of a second variation of the first embodiment in schematic form;

Figure 6 shows simulation results for the first embodiment in the form of a theta plot to show beam angle and an S-parameter plot between pairs of ports;

Figure 7 shows a plan view of a second embodiment in schematic form;

Figures 8a and 8b show plan views of a third embodiment in schematic form;

Figure 9 shows a perspective view of a fourth embodiment in schematic form;

Figure 10 shows a plan view of a fifth embodiment in schematic form;

Figure 11 shows a plan view of a sixth embodiment in schematic form;

Figure 12 is a simulation plot showing a radiation pattern of the embodiment of Figure 11 ;

Figure 13 shows a perspective view of a seventh embodiment in schematic form;

Figures 14a and 14b respectively show right hand and left hand circular polarisation effects in radiation patterns of the embodiment of Figure 13 fed from port 1 ;

Figures 15a and 15b respectively show right hand and left hand circular polarisation effects in radiation patterns of the embodiment of Figure 13 fed from port 2;

Figure 16 shows a perspective view of an eighth embodiment in schematic form; Figures 17a and 17b respectively show right hand and left hand circular polarisation effects in radiation patterns of the embodiment of Figure 16 fed respectively from port 1 and port 2;

Figure 18 shows a perspective view of a variation of the eighth embodiment in schematic form;

Figure 19 shows a perspective view of a ninth embodiment in schematic form;

Figure 20 shows a radiation pattern generated by the embodiment of Figure 19;

Figure 21 shows a perspective view of a tenth embodiment in schematic form; and

Figure 22 shows a radiation pattern generated by the embodiment of Figure 21. DETAILED DESCRIPTION

i) First embodiment:

[0059] A first embodiment, according to the first aspect and shown in Figure 4, comprises a conductive groundplane 1 above which is disposed a first half-width leaky- wave antenna (HW-LWA) 2 which has a stripline of conductive material in the form of a first main microstrip transmission line 3 between feed ports P2 and P4. The spacing between the first main microstrip transmission line 2 and the groundplane 1 is 25 mil (0.635mm), but this can be different, depending on the wavelength at which the antenna device is going to operate; in this case, 28GHz for 5G. A second HW-LWA 4 has a main microstrip transmission line 5 between feed ports P1 and P3, spaced above a groundplane 6 (which may be the same as the groundplane 1) by 10 mil (0.254mm). The main microstrip transmission lines 3, 5 are each joined along one edge to a central wall or septum 7, which is connected to the groundplane 1 , 6.

[0060] Each HW-LWA 2, 4 has an edge which is grounded by way of the septum 7, and together the two HW-LWAs 2, 4 form a back-to-back parallel arrangement with a delimiting centre line along a length of the septum 7. The grounding can be through a number of pins or vias connecting the main microstrip transmission lines 3, 5 to ground, or the grounding can be a continuous conductor such as a foil or metallic wall forming the common septum 7.

[0061] Each main microstrip transmission line 3, 5 has a corresponding subsidiary microstrip transmission line 8, 9 which runs parallel to its respective main microstrip transmission line 3, 5. A number of switchable or tuneable electronic components, in this particular instance varactors C1 C1 _n, C2rC2_n, connect each main microstrip transmission line 3, 5 to its respective subsidiary microstrip transmission line 8, 9. The electronic components may be evenly spaced or non-evenly spaced along the respective lengths of the microstrip transmission lines. The electronic components are addressable by a control processor (not shown) so as to enable the effective electrical width of each HW-LWA to be switched as required. Other switchable or tuneable elements could include fixed capacitors with switches or non-Foster elements or other impedance components.

[0062] Figures 5a to 5d illustrate two different ways in which the respective different spacings between the groundplane(s) 1 , 6 and the first and second main microstrip transmission lines 3, 5 can be obtained. In Figures 5a and 5b, the left hand main microstrip transmission line 3 has a height (hi) of 25mil from the main groundplane 1 , while the right hand main microstrip transmission line 5 extends lower down from the septum 7, resulting in a height (h2) of 10mil between the microstrip transmission line 5 and the groundplane 1. This first arrangement achieves the different groundplane heights by stepping the main microstrip transmission lines 3, 5 about the central septum 7 in an offset arrangement. In Figures 5c and 5d, the first and second main microstrip transmission lines 3, 5 are both at the same level (hi) above the main groundplane 1. However, an elevated groundplane 6 is formed over the main groundplane 1 underneath the second main microstrip transmission line 5, thus defining a smaller spacing (h2). In this case, a deposition of conductive layers 10, or a layer supported by conductive material such as foam, for example, or dielectric material with conductive vias, enables the main groundplane height to be raised towards the stripline, forming an intermediate groundplane 6 in order to obtain height h2, using common manufacturing techniques.

[0063] Such arrangements could be implemented on multilayer, or back-to-back bonded PCB technologies in order to facilitate economic mass production.

[0064] In operation this antenna would, for example as shown in Figure 4, take an RF feed at port P1 with the smaller height. The useful beam angle, adjusted by providing and increasing voltage to the varactor array, would start at 10 degrees and sweep to 35 degrees whereby the efficiency would drop away. To continue from 35 degrees, the feed would then switch to port P2 utilising the antenna with the largest height. This would effectively reset the efficiency and allow a useful sweep to continue from 35 degrees to 60 degrees.

[0065] Figure 6 features two tables of simulation results to illustrate this multi-height feature advantage and how it works in practice. The simulation used an antenna arrangement similar to that shown in Figure 5, but with slightly different substrate heights of 5mil and 15mil, and with an array of varactors with a range of 0.1 pF (18v) to 1 pF (Ov). The Theta plot illustrates how the application of voltage to the varactor array changes the angle of the beam produced (0 is broadside and 90 is endfire). In this example, sweeping is between 30 degrees and 65 degrees, for both antennas and with an indication of the varactor driving voltage.

[0066] The second plot in Figure 6 entitled "S31 S42" gives an indication of the power delivered from port P1 to port P3, which is 50-ohm loaded, on one HW-LWA, and from port P2 to port P4 on the other HW-LWA respectively. Ideally, the S-parameter should remain a large negative value to indicate transmission line insertion loss (i.e. the antenna is emitting), as this value approaches zero it is indicative that the arrangement is behaving as a transmission line and not radiating efficiently.

[0067] It is evident that as the 5 mil antenna approaches 60 degrees, the radiation efficiency is dropping to unusable levels (as -3db or half of the signal power is delivered to the load, or not radiated). When the switch is made to the larger height antenna, the efficiency is reset (as -13.7db or 4 percent of the signal power is delivered to the load, therefore 96% radiated) in order to take the sweep angle further. It is this configuration that allows the extended usable sweep from 30-65 degrees.

[0068] The effects of squint on the antenna are considered to be negligible in these embodiments. This is because a relatively small operating bandwidth of 500MHz has been chosen at the operating frequency of 28GHz, in accordance with the current 5G standards. This means that any squint effects are less than the half-power beam width and therefore can be effectively ignored.

ii) Second Embodiment:

[0069] A second embodiment, according to the second aspect and shown in Figure 7, provides the reconfigurable aspect by using an array of conductive elements connected to ground at various points along the length of each of first and second microstrip transmission lines 3, 5. In this embodiment, it is not necessary to provide subsidiary microstrip transmission lines as in the first embodiment. Switches SW1 SW1_n, SW2i- SW2_n are controlled by a control processor (not shown) so as selectively to switch the respective microstrip transmission lines 3, 5 to ground at such points. This controls the effective width of each microstrip transmission line 3, 5 and hence the angle of the beam.

[0070] In operation, if all switches are closed, this gives the theoretical minimum width of the microstrip transmission line. Similarly, if all the switches are left open, this gives the theoretical maximum electrical width of the microstrip transmission line. However, if only a subset of the switches is closed, with the remaining switches left open, this produces an electrical width somewhere between the maximum and minimum, with the width dependent on the number of switches closed versus those left open in a mixed switch- state arrangement. iii) Third Embodiment:

[0071] Rather than using the back-to-back configuration to enable a full sweep of usable angles, each antenna can be driven simultaneously at the same frequency. In this configuration, as shown in Figures 8a and 8b two equal width HW-LWAs 2, 4 with opposing feeding ports P1 , P2; P3, P4 can produce two separate beams in different directions. In conjunction with the previously discussed reconfigurable electronic components (see First Embodiment above), each beam can be independently, and simultaneously, swept across a range of angles from broadside (0°) to endfire (+90°, -90°) to cover space. In Figure 8a, ports P2 and P3 are fed with an RF signal to produce the opposing beams. In Figure 8b, ports P1 and P4 are fed with an RF signal to produce a similar effect but with the beam direction reversed. This enables a full sweep from 0° to +90° and from 0° to -90°.

iv) Fourth Embodiment:

[0072] As the effective width of the microstrip transmission line 3, 5 dictates the frequency of operation, the antennas 2, 4 of the back-to-back configuration could have different widths corresponding to different frequency bands. An illustration of this embodiment is shown in Figure 9.

[0073] Two HW-LWA microstrip transmission lines 3, 5 are arranged in a parallel back- to-back configuration, sharing the common ground septum 7. In this case, the widths have been optimised for operation at 28GHz and 60GHz frequencies.

v) Fifth Embodiment:

[0074] Various feeding techniques may be employed to generate particular beam shapes or patterns from the antenna arrangement.

[0075] An arrangement of two back-to-back HW-LWAs 2, 4, sharing a common septum 7, can be fed differentially. This is where one port is fed 180° out of phase with the other, as in a balanced feed arrangement. Figure 10 illustrates such an arrangement, the feed 1 1 is split and a balun, or other appropriate phase-delay network or circuit 12, is used to produce a 180-degree phase shift between split feeds 13 and 13'.

[0076] This arrangement produces two isolated (independent) lobes with minimal interaction, and can therefore transmit to two receiving nodes in the same vicinity with full data rates. Similarly, the feeds can be switched to the other end of the microstrip transmission lines to reverse the beam directions. An alternative arrangement could also be to feed one side of the antenna 2 from the left and then feeding the 180-degree phase shifted signal from the right on antenna 4, to create two opposed isolated beams. [0077] The feed 11 can also be split and fed onto antennas 2 and 4 without any phase difference. This still creates two beams, however there is no isolation and they interact to form one larger lobed beam. Such a feeding arrangement would allow for the size (length) of the antenna arrangement to be reduced if such space requirements necessitate a smaller footprint.

vi) Sixth Embodiment:

[0078] Another arrangement, illustrated in Figure 1 1 , shows a single HW-LWA 2 being centre-fed. The signal splits at the centre feed-point 11 and traverses along the antenna in two opposing directions along the microstrip transmission line 3.

[0079] This results in two separate radiation lobes being formed from the different and opposing directions of the signal on the microstrip transmission line 3, illustrated in the simulated radiation pattern in Figure 12.

vii) Seventh Embodiment:

[0080] The HW-LWA arrangement does not have to be limited to a linear, rectangular shape. Another useful shape would be a curved or half-moon arrangement, in order to produce specific radiation properties, for example as shown in Figure 13 with like parts being labelled as in previous embodiments.

[0081] This particular arrangement produces circularly polarised radiation, dependent on which port is being fed. In operation, when fed at port P1 (on the right-hand side), the emitted radiation is right-hand circularly polarised, as the septum 7 is seen on the left hand of the travelling waves. Similarly, when fed from port P2 (on the left-hand side), the emitted radiation is left-hand circularly polarised, as the septum is seen on the right hand of the travelling waves. The HW-LWA antenna is as described in the earlier embodiments, with a main microstrip transmission line 3, and the inner edge of the arc being the line of connection to the grounded septum 7, which also follows a curved path. Feeding points P1 and P2 are provided at either end. Simulations of both feeding scenarios are illustrated in Figures 14 and 15.

[0082] Each plot in Figures 14 and 15 illustrates the circular polarised radiation patterns from the antenna arrangement in CST (a software package from CST Computer Simulation Technology AG).

[0083] Figure 14a shows the simulated radiation plot for right-handed polarised emissions from the embodiment of Figure 13 fed from port PL Figure 14b shows the simulated radiation plot for left-handed polarised emissions from the embodiment of Figure 13 fed from port PL It is clear that there are main lobes for left-handed polarisation, but very little for the right-handed polarisation. [0084] Figures 15a and 15b shows similar plots of left- and right-handed circularly polarised radiation patterns for the arrangement of Figure 13 fed through port P2. It is evident from the plots that the main lobe is present for right-handed circularly polarised emission.

[0085] This embodiment allows polarisation characteristics to be imparted on the radiation as well as other characteristics such as angular control from the addition of reconfigurable elements, as described earlier. Such control of polarisation is particularly useful in satellite communications.

[0086] The polarisation derives from the changing direction of the travelling wave as it traverses around the arc. This change in direction imparts a continuous phase change to the emitted wave, which in a quarter of a turn equates to 90 degrees. Therefore, the quarter turn length is chosen to be a quarter wavelength.

[0087] The arrangement has high port-to-port isolation, therefore another scenario could be that the device is fed simultaneously through ports P1 and P2. This would result in two opposite direction beams also with opposing polarisations.

[0088] It has also been determined experimentally that extending the length of the curved radiator improves the directivity of the produced beam.

[0089] A number of quarter-turn, quarter wavelength curved HW-LWA radiating elements 13 can be arranged over a groundplane 1 in a serpentine fashion as shown in Figure 16.

[0090] The extended HW-LWA arrangement has two ports P1 , P2 and can be fed from either, in order to control the polarisation of the emitted radiation as already discussed. Figures 17a and 17b respectively show the simulated radiation patterns from being fed from each of the ports P1 and P2.

[0091] The main lobe is narrower and more defined than in the previously-discussed arrangement of just a half-turn (2 quarter-wave curved elements) shown in Figures 14 and 15. It is also clear that, in agreement with the simulations for the single curved element, being fed from port P1 when the septum 7 is on the right hand of the travelling wave produces left-hand circularly polarised radiation, and when fed from port P2 produces right-hand circularly polarised radiation.

[0092] Other designs of the curve in relation to the wavelength are also possible, for example the 90° turn can represent a half-wavelength rather than a quarter-wavelength as previously described. [0093] Another arrangement for the serpentine antenna design makes use of the earlier HW-LWA back-to-back arrangement (such as that detailed in the First Embodiment section above), but using similar height groundplanes 1.

[0094] This back-to-back serpentine arrangement is shown in Figure 18.

[0095] The antenna arrangement has four ports P1-P4 addressing each side of the two, curved back-to-back, half-width leaky-wave devices with a shared central ground septum 7. The previous 2-port implementation is limited in that the septum 7 is seen on different sides, dependent on which port is being fed. Accordingly, as well as the polarisation changing, the beam direction also changes.

[0096] The enhanced 4-port implementation shown in Figure 18 allows the direction of the beam to remain the same, being fed from one side e.g. P1 & P3 or P2 & P4, with the polarisations of the beams being differently circularly polarised.

[0097] Similar to the single arrangement, due to the high port-to-port isolation, one element can be driven simultaneously in both directions. For example, the top half of the serpentine arrangement (in Figure 18) can be driven simultaneously by ports P1 and P2, and results in dual beam (opposite angles) and also opposite polarisation.

viii) Eighth Embodiment:

[0098] The size of the main groundplane 1 can be adjusted in order to shape the radiation pattern. It is well-known in antenna design that the size and shape of the groundplane 1 can affect radiation from a radiating element. For example, a large groundplane 1 will act as a large reflector for emission in generally perpendicular directions, or may deflect the radiation in the plane.

[0099] If the HW-LWA 2 is arranged above a groundplane 1 that is substantially the same size as the microstrip transmission line 3, with the septum 7 along one edge of the groundplane 1 , the radiation pattern appears to be reflected, creating a narrow circular distributed main lobe pattern both above and below the antenna 2. This arrangement is shown in Figure 19, and the resultant radiation pattern is illustrated in Figure 20.

[00100] A large groundplane 1 , as seen in the earlier embodiments, blocks the downward lobe, resulting in a single upward lobe that moves from broadside to endfire either with frequency or from reconfigurability of the antenna structure.

ix) Ninth Embodiment:

[00101] In addition to the planar embodiments described above, the main microstrip transmission line 3 of the HW-LWA can be curled around the septum 7 to form a partial, or full tube type structure. A partial tube curled arrangement in comparison to the usual planar microstrip transmission line arrangement is shown in Figure 21.

[00102] The effect of curling the main microstrip transmission line 3 around the septum 7 appears to give a similar result to the small groundplane embodiment whereby the main lobe is spread above and below the antenna. Both the microstrip transmission line 3 and the associated groundplane 1 are curled so as to maintain a consistent separation distance.

[00103] The associated simulated radiation pattern is illustrated in Figure 22.

[00104] It should be noted that various combinations of these embodiments are also disclosed by way of this description, and also variants whereby the devices are reconfigurable using switchable or tuneable elements located on the strip-line, in order to produce beam patterns and directivities useful for the specific purpose. It should also be noted that the antenna arrangements can also be designed, and optimised, for operation in other microwave communication bands such as those of the 2.4 and 5 GHz wireless local area networking (WLAN) or WiFi, 60GHz WiGig, or other mobile telecommunications standards; and not just limited to those defined in the examples contained in the embodiments herein.

[00105] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00106] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. [00107] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS:

1. A reconfigurable, leaky-wave antenna device comprising:

a groundplane;

a first main microstrip transmission line having first and second opposed lengthwise edges, the first edge connected to the septum, the first main microstrip transmission line extending substantially parallel to and above the groundplane to one side of the septum; and

a first subsidiary microstrip transmission line, arranged alongside the second edge of the first main microstrip transmission line;

2. An antenna device as claimed in claim 1 , further comprising:

3. An antenna device as claimed in claim 2, wherein the first main and the first subsidiary microstrip transmission lines are spaced from the groundplane by a first distance and the second main and second subsidiary microstrip transmission lines are spaced from the groundplane by a second distance different from the first distance.

4. An antenna device as claimed in claim 3, wherein the first main and the first subsidiary microstrip transmission lines are in a first plane and the second main and second subsidiary microstrip transmission lines are in a second plane different from the first plane.

5. An antenna device as claimed in claim 3, wherein the first and second main and subsidiary microstrip transmission lines are all in the same plane, and wherein the groundplane on one side of the septum is elevated relative to the groundplane on the other side of the septum.

6. An antenna device as claimed in any one of claims 2 to 5, wherein the first and second main microstrip transmission lines are of different widths.

7. An antenna device as claimed in any preceding claim, wherein the reconfigurable electronic components are selected from the group consisting of: varactors, impedance networks, non-Foster elements, tuneable capacitors, and RF switches.

8. A first antenna device as claimed in claim 1 , in combination with a second antenna device also as claimed in claim 1 , wherein the antenna devices are arranged parallel to each other and wherein the first antenna device is fed from one end to allow beam steering in a range from -90° to 0° relative to a normal to the antenna devices, and wherein the second antenna device is fed from an opposite end to allow beam steering in a range from 0° to 90° relative to the normal to the antenna devices.

9. A reconfigurable, leaky-wave antenna device comprising:

a groundplane;

10. An antenna device as claimed in claim 9, wherein the first microstrip transmission line is in a first plane and the second microstrip transmission line is in a second plane different from the first plane.

1 1. An antenna device as claimed in claim 9, wherein the first and second microstrip transmission lines are in the same plane, and wherein the groundplane on one side of the septum is elevated relative to the groundplane on the other side of the septum.

12. An antenna device as claimed in any one of claims 9 to 11 , wherein the first and second microstrip transmission lines are of different widths.

13. An antenna device as claimed in any one of claims 9 to 12, wherein the electronic components are selected from the group consisting of: varactors, impedance networks, non-Foster elements, tuneable capacitors, and RF switches.

14. An antenna device as claimed in any preceding claim, wherein the septum and the microstrip transmission lines follow a straight path.

15. An antenna device as claimed in any one of claims 1 to 13, wherein the septum and the microstrip transmission lines follow a curved path.

16. An antenna device as claimed in claim 15, wherein the septum and the microstrip transmission lines follow a serpentine path.

17. An antenna device as claimed in claim 16, comprising a linear array of septum and microstrip subunits, each subtending an arc of substantially 90° or of substantially 180°, the subunits being arranged such that the linear array follows the serpentine path.

18. An antenna device as claimed in claim 17, wherein the arc of substantially 90° has a length of substantially one quarter of a wavelength of operation, or wherein the arc of substantially 180° has a length of substantially one half of a wavelength of operation.

19. An antenna device as claimed in any one of claims 1 to8, wherein the main microstrip transmission line is curled across its width, with the groundplane correspondingly curled to maintain a substantially constant separation distance from the main microstrip transmission line.

20. An antenna device as claimed in any one of claims 9 to 13, wherein the first and/or second microstrip transmission line is curled across its width, with the groundplane correspondingly curled to maintain a substantially constant separation distance from the respective first and/or second microstrip transmission line.

21. An antenna device as claimed in claim 19 or 20, wherein the groundplane and respective microstrip transmission line are curled to form a full or partial tube structure.

22. An antenna device as claimed in any preceding claim, wherein the septum is formed from at least one of: solid metal, metal foil, and a linear array of conductive pins or vias connecting the groundplane to the respective main or first or second microstrip transmission line.

23. An antenna device as claimed in any preceding claim, further comprising a control processor to control the electronic components.

24. An antenna device as claimed in claim 23, wherein the control processor is operable to steer an angle of a beam radiated by the antenna device.

25. An antenna device as claimed in claim 24, wherein the angle of the beam is steerable, in relation to a normal, between broadside (0°) and endfire (±90°) directions.

26. An antenna device as claimed in any one of claims 23 to 25, wherein the control processor is operable to change an effective electrical width of the respective microstrip transmission line by switching in or out one or more of the electronic components.

27. An antenna device as claimed in any one of claims 23 to 26, wherein the control processor is operable to change an effective electrical length of the respective microstrip transmission line by switching in or out one or more of the electronic components.

28. An antenna device as claimed in any one of claims 23 to 27, wherein the control processor is operable to switch a feed from one microstrip transmission line to another, and/or to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line.

29. An antenna device as claimed in any one of claims 23 to 28, wherein the control processor is operable to detect an efficiency of the antenna device, and to reconfigure the electronic components and/or the feeding of the microstrip transmission line(s) in order to maintain efficiency.

30. An antenna device as claimed in any one of claims 23 to 29, wherein the control processor is operable to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line so as to change a circular polarisation property of a radiated beam.

31. An antenna device as claimed in any one of claims 23 to 30, wherein the control processor is operable to switch a feed from one end of a respective microstrip transmission line to another end of the respective microstrip transmission line so as to invert an angle of a radiated beam relative to broadside.

32. An antenna device as claimed in any preceding claim, implemented on a multilayer PCB.

33. An antenna device as claimed in any preceding claim, configured for beam-forming or MIMO operation.