Antenna

Abstract

An antenna comprising: a high impedance surface ground plane; a plurality of antenna elements each arranged to curve around a common longitudinal axis extending from the high impedance surface ground plane; and a feeding network configured to apply a plurality of different combinations of phase angles of an input signal to the plurality of antenna elements, thereby to enable the formation of a plurality of different radiation patterns.

Description

ANTENNAFIELD OF THE INVENTION

[0001] The invention relates to an antenna-based apparatus and systems and methods of operating the apparatus and systems. In particular, but not exclusively, the invention relates to antenna elements, arrays of antenna elements and wireless power transmission using antenna elements.BACKGROUND

[0002] Wireless power transmission systems have the potential to enhance a wide range of technologies. For example, transmitting antennae are known to be used in combination with rectennas to facilitate power transfer between multiple devices by microwave radiation.However, a main challenge in such wireless power transmission systems is to achieve a high Beam Collection Efficiency (BCE), which is the ratio between the power received on the rectenna (Pr) and the transmitted power of the transmitting antenna (Pt). The BCE is dependent on a number of factors, such as the focus of the transmitted beam, alignment of the transmitting antenna to the rectenna and RF to DC conversion efficiency of the rectenna. Some of the difficulties involved in achieving a high BCE are exacerbated over increased distances. It is an object of the disclosure to at least partly address one or more of the shortcomings in the prior art.SUMMARY OF THE INVENTION

[0003] According to an aspect of the invention, there is provided an antenna comprising: a high impedance surface ground plane; a plurality of antenna elements each arranged to curve around a common longitudinal axis extending from the high impedance surface ground plane; and a feeding network configured to apply a plurality of different combinations of phase angles of an input signal to the plurality of antenna elements, thereby to enable the formation of a plurality of different radiation patterns.

[0004] There is also provided a vector phased array comprising a controller and a plurality of antennae. There is also provided a wireless power transfer system comprising: a rectenna; and one or more antennae.

[0005] Advantageously, a pattern-reconfigurable helix antenna is provided with improved focusing and steerability. Implementation of such an antenna in a vector phased array and / or power transfer system provides improved focusing and steerability, which in turn facilitates improved beam collection efficiency.

[0006] Optionally, the antenna elements are helical antenna elements extending from the high impedance surface ground plane along the common longitudinal axis. Optionally, the helical antenna elements are formed on the surface of a cylindrical member.

[0007] Optionally, the feeding network is further configured to apply different relative phases of the input signal to at least two of the plurality of antenna elements. Optionally, the feeding network comprises a digital beamforming circuit. Optionally, the feeding network comprises a plurality of power divider circuits corresponding to the plurality of different combinations of phase angles of an input signal applied to the plurality of antenna elements. Advantageously, a digital beamforming circuit enables wide-ranging dynamic control over the phase angles of inputs at the antenna elements, thereby dynamically to reconfigure a radiation pattern associated with the antenna. Beneficially, power dividers provide elegant solutions for the implementation of different phase combinations without the need for further external circuitry. Beneficially, multiple power dividers can be provided and connected to the antenna, thereby to enable switching between different radiation patterns associated with the antenna.

[0008] Optionally, the antenna is a circularly polarised antenna, optionally wherein the antenna is a right-hand circularly polarised antenna and / or a left-hand circularly polarised antenna. Advantageously, circularly polarised radiation transmitted by an antenna facilitates alignment, making such an antenna suitable for long distance power transmission.

[0009] Optionally, at least one combination of the plurality of different combinations of phase angles of an input signal comprises a difference in phase angle applied to two of the antenna elements of: 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300° and / or 330°. Advantageously, preselected combinations of phase difference enable simple reconfigurability of an antenna, thereby to control the radiation pattern associated with the antenna.

[0010] Optionally, the antenna is a quadrifilar helix antenna comprising four antenna elements. Beneficially, quadrifilar helix antennae provide a wide range of radiation pattern control and fabrication benefits.

[0011] Optionally, the plurality of different combinations of phase angles of an input signal comprises: a first mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 90°, 180° and 270°; and / or a second mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 90°, 90° and 180°; and / or a third mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 120°, 60° and 180°. Advantageously, such mode combinations are shown to provide radiation patterns that can be selected for improved steerability and power transmission.

[0012] Optionally, the high impedance surface ground plane is an artificial magnetic conductor ground plane comprising a plurality of electrically conductive regions formed on a surface of a dielectric substrate. Optionally, each electrically conductive region of the plurality of electrically conductive regions is in electrical communication with an electrically conductive common plane on an opposite surface of the dielectric substrate to the plurality of electrically conductive regions. Optionally, the plurality of electrically conductive regions is arranged in an array having an array pitch corresponding to an operating frequency of the antenna. Advantageously, such high impedance surface ground planes are shown to enable high-quality directional control of radiation patterns generated by the antenna.

[0013] Optionally, the antenna is configured to transmit power, optionally wherein the transmitted power is at least 1 W, optionally wherein the transmitted power is at least 10 W, optionally wherein the transmitted power is at least 100 W, optionally wherein the transmitted power is at least 1 kW, optionally wherein the transmitted power is at least 1 MW, optionally wherein the transmitted power is at least 1 GW. Beneficially, the antenna can be configured to transmit power in accordance with a wide range of powers corresponding to a wide range of implementations.

[0014] Optionally, the antenna elements are spiral antenna elements substantially flat to the high impedance surface ground plane.

[0015] Optionally the plurality of antenna elements are metal elements printed on a flexible film. Beneficially, an elegant route to fabrication of such antennae is provided.

[0016] Optionally, one or more antennae and / or a vector phased array comprising one or more antennae, are mounted on a satellite. Optionally, the one or more antennae and / or the vector phased array are configured to transmit power of at least 1 W, optionally at least 10 W, optionally at least 100 W, optionally at least 1 kW, optionally at least 1 MW, optionally at least 1 GW. Advantageously, such antennae provide improved power transmission over large distances.

[0017] There is also provide a method of operating an antenna, the method comprising: determining a beam direction; selecting a combination of phase angles of an input signal from the plurality of different combinations based on the beam direction; and applying the combination of phase angles of an input signal to the plurality of antenna elements, thereby to enable optimisation of gain associated with the beam direction.

[0018] Optionally, the method further comprises varying the relative phase of the input signal at each of the plurality of antenna elements. Optionally, the method further comprises transmitting power in the beam direction. Advantageously, the pattern-reconfigurable nature of the antenna enables gain optimisation to be achieved for power transmission in a fast and efficient manner.

[0019] There is also provided a method of operating the comprising: sequentially applying different combinations of the plurality of different combinations of phase angles of an input signal to the plurality of antenna elements; and transmitting a signal and detecting a response to the transmitted signal associated with one of the plurality of different combinations of phase angles of an input.

[0020] Optionally, the method comprises varying the relative phase of the input signal at each of the plurality of antenna elements. Optionally, the method comprises using the detected response to identify an object associated with the detected response. Advantageously, the patternreconfigurability of the antenna enables switching of the antenna to cover different areas to search for a response, thereby enable efficient radio frequency identification and optionally subsequent power transmission.

[0021] There is also provided a method of wirelessly transferring power comprising: determining a beam direction based on the location of the rectenna with respect to one or more antennae and / or a vector phased array; selecting a combination of phase angles of an input signal from the plurality of different combinations based on the beam direction; applying the combination of phase angles of an input signal to the plurality of antenna elements, thereby to enable an improvement in gain optimisation associated with the beam direction; and transmitting power from the one or more antennae and / or the vector phased array to the rectenna.

[0022] Further aspects of the invention will be apparent from the description and the appended claimsDETAILED DESCRIPTION

[0023] A detailed description of embodiments is described, by way of example only, with reference to the figures, in which:Figure l is a perspective view of a quadrifilar helix antenna;Figures 2A and 2B are perspective views of configurations of quadrifilar helix antennae Figure 3 is a plan view of a high impedance surface;Figure 4 is a plan view of a quadrifilar helix antenna;Figures 5A, 5B and 5C are views of power divider networks;Figure 6 is a schematic of a wireless power transfer system;Figure 7 shows three simulated 3D radiation patterns corresponding to different input phase combinations;Figure 8 shows three 3D radiation patterns corresponding to different input phase combinations;Figures 9A and 9B show plots of measured S-parameters and phase differences for a first mode of input phase combinations;Figure 10A and 10B show plots of measured S-parameters and phase differences for a second mode of input phase combinations;Figures 11 A and 1 IB show plots of measured S-parameters and phase differences for a third mode of input phase combinations;Figures 12 A, 12B and 12C show plots of measured |Sn| results for three different power dividers;Figures 13A, 13B and 13C show plots of simulated and far-field radiation patterns for three different modes of input phase combinations;Figure 14 is a plan view of a quadrifilar spiral antenna; and Figures 15A and 15B show configurations of antenna arrays comprising a plurality of pattern reconfigurable antennae.

[0024] A pattern-reconfigurable helix antenna, which may be used as the unit of a transmitting array is described herein. The pattern-reconfigurable helix antenna, which may be a quadrifilar helix antenna (QHA), provides improved focussing and steerability, thereby to enable improved efficiency of energy transfer to a receiving antenna.

[0025] Figure 1 shows a perspective view of a pattern-reconfigurable helix antenna 100. There is shown a high-impedance ground plane 102 and a plurality of helical antenna elements 112. The plurality of helical antenna elements is arranged such that each of the elements curve around a common longitudinal axis extending from the high impedance surface ground plane. In an example, the common longitudinal axis extends in a direction substantially normal to the substantially planar surface of the high impedance surface ground plane. In further examples, the common longitudinal axis extends in a different direction whilst providing the functionality described herein. The antenna 100 also includes a feeding network 116 configured to apply a plurality of different combinations of phase angles of an input signal to the plurality of helical antenna elements 112 of the antenna 100, thereby to enable the formation of a plurality of different radiation patterns. Advantageously, in an example the feeding network 116 is configured to apply different relative phases of the input signal to at least two of the plurality of helical antenna elements 112. Whilst the antenna 100 of Figure 1 is shown to be a quadrifilar helix antenna having four antenna elements, in further examples the antenna 100 has a plurality of helical antenna elements 112 of any number.

[0026] In the example of Figure 1, the plurality of helical antenna elements 112 are formed on the surface of a cylindrical member 113, optionally wherein the plurality of helical antennaelements 112 are metal elements printed on a flexible film. Advantageously, a plurality of metallic elements is formed on a substantially flat flexible polyimide film and subsequently rolled in a precise manner to form the plurality of helical antenna elements 112. Whilst the plurality of helical antenna elements 112 of Figure 1 is shown to be formed around a hollow cylindrical member 113, in further examples additional material is included within the cylindrical member 113, for example in order to aid antenna performance and / or fabrication.

[0027] Alternatively, the helical antenna elements 112 may be formed not around a cylindrical member 113, but around a different shape such as a conical surface or other quadric surface having a changing diameter along the common longitudinal axis extending from the high impedance surface ground plane.

[0028] The plurality of helical antenna elements 112 are subsequently each welded to a microstrip feedline 118, 120, thereby to enable delivery of input signals. Whilst the antenna 100 shown at Figure 1 is formed in this manner, in further examples alternative and / or additional techniques are used to provide the antenna 100. Configurations of pluralities of helical antenna elements, which may be implemented alternatively or additionally to the plurality of helical elements 112 shown at Figure 1, are described in further detail with reference to Figure 2, below.

[0029] A high impedance surface is used as the ground plane 102 of the antenna 100, thereby to provide high gain and improved steerability. The high impedance surface ground plane 102 is formed from an array of periodic conductive patches 115 on a dielectric substrate 114. Figure 3 shows a plan view of an example of the high impedance surface ground plane 102 in further detail. There is shown a dielectric substrate 114 upon which a plurality of conductive regions 115 are formed in a periodic array. Each conductive region 115 includes a via 103 through the conductive region 115 and a corresponding portion of the dielectric substrate 114. The dielectric substrate 114 is arranged on an electrically conductive common plane 117, as shown at Figure 1. In an example, the electrically conductive common plane 117 is a metal ground and the via 103 comprises metal, thereby to provide electrical conductivity between the electrically conductive regions 115 and the electrically conductive common plane 117. As shown at Figure 3, the electrically conductive regions 115 are arranged with a periodic pitch along at least two axes 105, 107. In an example, the plurality of electrically conductive regions 115 is arranged in an array having an array pitch corresponding to an operating frequency of the antenna.Beneficially, the array pitch provided by the periodic spacing of the electrically conductive regions 115 is based on an operating frequency of the antenna 100, thereby to provide enhanced functionality at the operating frequency. Whilst the electrically conductive regions 115 are shown to be rectangular patches, in further examples, the electrically conductive regions 115 are additionally or alternatively formed with any appropriate geometry. In further examples, the highimpedance surface ground plane 102 is formed using any appropriate technique and with any appropriate configuration of materials and geometry in order to provide the improved power transmission as described herein.

[0030] Accordingly, in an example, the high impedance surface ground plane 102 is an artificial magnetic conductor ground plane comprising a plurality of electrically conductive regions 115 formed on a surface of a dielectric substrate 114. Optionally, each electrically conductive region 115 of the plurality of electrically conductive regions 115 is in electrical communication with an electrically conductive common plane 117 on an opposite surface of the dielectric substrate 114 to the plurality of electrically conductive regions 115. Advantageously, the high impedance surface ground plane 102 functions as an artificial magnetic conductor (AMC) surface that suppresses surface current, thereby enhancing radiation propagated by the antenna 100 in the direction away from the high impedance surface ground plane 102.

[0031] The feeding network 116 shown at Figure 1 includes a number of feedlines 118, 120 to provide input signals to a respective helical antenna element of the plurality of helical antenna elements 112. Whilst two feedlines are shown, the number of feedlines is any appropriate number to facilitate routing of an input signal to each of the plurality of helical antenna elements 112. Input signal controls to a quadrifilar helix antenna are shown in further detail with reference to Figure 4. Figure 4 shows a plan view of a quadrifilar helical antenna 400 formed on a plane 402, which, in an example, is the antenna 100 comprising a plurality of helical antenna elements 112 extending from the high impedance surface ground plane 102 described with reference to Figure 1. There are shown four helical antenna elements 404, 406, 408, 410, which in an example are the helical antenna elements of the plurality of helical antenna elements 112 of the antenna 100 described with reference to Figure 1. Each helical antenna element 404, 406, 408, 410 has a corresponding input signal port 403, 405, 407, 409. The input signal ports 403, 405, 407, 409 provide connection through plane 402. In the example of the antenna 100 of Figure 1, each helical antenna element of the plurality of helical antenna elements 112 is associated with a respective one of the input signal ports 403, 405, 407, 409 thereby to provide a connection through the high impedance surface ground plane 102 in order to receive signals provided by the feeding network 116. Whilst a particular configuration for providing input signals to each of the helical antenna elements is shown, in further examples additional or alternative components are provided in any appropriate arrangement in order to enable input signals to be applied to the individual helical antenna elements of the plurality of helical antenna elements 112 of the antenna 100.

[0032] Figure 14 shows another example of a quadrifilar antenna that is different from the helical antenna depicted by Figure 4. Figure 14 shows a plan view of a quadrifilar spiral antenna450 formed on a plane 412, which, in an example, is the antenna 100 comprising a plurality of antenna elements. There are shown four spiral antenna elements 414, 416, 418, 420 formed substantially flat on the surface of plane 412 as alternatives to the helical antenna element 404, 406, 408, 410 extending vertically from the plane 402. Each spiral antenna element 414, 416, 418, 420 has a corresponding input signal port 413, 415, 417, 419. While a quadrifilar spiral antenna 450 is show, in further examples the antenna has a plurality of spiral antenna elements of any number.

[0033] The input signal ports 413, 415, 417, 419 provide connection through the plane 412 for each of the spiral antenna elements 414, 416, 418, 420 in order to receive signals provided by the feeding network 116. The quadrifilar spiral antenna 450 has a reduced space requirement compared to the quadrifilar helical antenna 400 because it is formed substantially flat on the surface of the plane 412. Quadrifilar spiral antenna 450 exhibits reduced mutual coupling because of a reduction in vertical current component from the substantially flat spiral antenna elements 414, 416, 418, 420. This reduced mutual coupling may improve the beam collection efficiency for the spiral antenna compared to the helical antenna.

[0034] The feeding network 116 shown in the pattem-reconfigurable helix antenna 100 of Figure 1 is configured to apply a plurality of different combinations of phase angles of an input signal to the plurality of helical antenna elements 112, thereby to enable the formation of a plurality of different radiation patterns. Advantageously, the application of different combinations of phase angles to the feeding ports of the helical antenna elements changes the maximum gain and the distribution of the gain of the radiation pattern corresponding to the different combinations of phase angles. This means that changing the different combinations of phase angles to the plurality of helical antenna elements 112 enables different properties of the antenna 100 to be exploited. Beneficially, as described further herein, forming an array of pattern reconfigurable antennae 100 synergistically enables the combination of phase angles of an input signal for a single antenna 100 to be determined based on the operating conditions of the whole array. Advantageously, the combination of phase angles of an input signal for individual antennae 100 can be chosen to provide optimisation of gain associated with the beam direction of the array.

[0035] Table 1 below shows examples of different combinations of phase angles of an input signal that can be applied to the plurality of helical antenna elements, such as the plurality of helical antenna elements 112 of the antenna 100 described with reference to Figure 1. In the example of Table 1, there are three modes, each corresponding to different combinations of phase angles of an input signal applied to the helical antenna elements of a quadrifilar helix antenna having four helical antenna elements each arranged to curve around a commonlongitudinal axis. For each mode, the variation in gain is shown for different conditions, as described below.

[0036] There is a first mode, Mode 1, wherein the phase angles applied to sequentially adjacent helical elements on a path around the common longitudinal axis of the plurality of helical antenna elements are: 0°, 90°, 180° and 270°. There is a second mode, Mode 2, wherein the phase angles applied to sequentially adjacent helical elements on a path around the common longitudinal axis are: 0°, 90°, 90° and 180°. There is a third mode, wherein the phase angles applied to sequentially adjacent helical elements on a path around the common longitudinal axis are: 0°, 120°, 60° and 180°.

[0037] The values in Table 1 are based on simulated data for a configuration of an antenna pointing in a particular direction. In the example of Table 1, the antenna, which may correspond to the antenna 100 of Figure 1, is arranged such that the plurality of helical antenna elements are each arranged to curve around a common longitudinal axis extending from a ground plane. The common longitudinal axis coincides with the z-axis that is substantially perpendicular to ground plane and defines an elevation of 0 = 0°.

[0038] Simulated 3D radiation patterns for Mode 1, Mode 2 and Mode 3 are shown at Figure 7. The patterns of Figure 7 are simulated for an antenna having a near perfect magnetic conductor as a ground plane. In the simulations shown at Figure 7, a material with a very high surface impedance of 1O6'Q was used. Figure 7 shows a simulated 3D radiation pattern 700A corresponding to Mode 1, a simulated 3D radiation pattern 700B corresponding to Mode 2 and a simulated 3D radiation pattern 700C corresponding to Mode 3. In Figure 7, the z-axis 702A, 702B, 702C of each of Mode 1, Mode 2 and Mode 3, respectively, defines an elevation 704A, 704B, 704C of 0 = 0°. It can be seen from the simulated 3D radiation patterns 700A, 700B, 700C, that different combinations of phase angles of an input signal applied to the plurality of helical antenna elements results in different shapes of radiation patterns. For example, the simulated 3D radiation pattern 700A corresponding to Mode 1 has a beam direction following the arrow 706A coinciding with the z-axis. In contrast, the simulated radiation pattern 700B corresponding to Mode 2 has a beam direction following an arrow 706B that points in a different direction and the simulated radiation pattern 700C corresponding to Mode 3 has a beam direction following an arrow 706C that points in a yet further different direction. Selected data values from the simulated 3D patterns 700A, 700B, 700C corresponding to Mode 1, Mode 2 and Mode 3 respectively, are shown at Table 1.

[0039] For example, as shown at Table 1, the maximum realised gain in dBi that is achieved for different modes is different and the beam directions of the different modes vary. For example, Mode 1 is directed in a direction with an elevation of 0 = 0° and azimuthal angle of = 0°.Mode 1 has a maximum, realised gain of 8.70 dBi. Mode 2 is directed in a direction with an elevation of 0 = 24° and azimuthal angle of O = 258°. Mode 2 has a maximum, realised gain of 8. 02 dBi. Mode 3 is directed in a direction with an elevation of 0 = 29° and azimuthal angle of = 258°. Mode 3 has a maximum, realised gain of 6.93 dBi. Further, as shown at Table 1, the variation in gain in dB on different planes of elevation is different for the different modes.

[0040] The values shown at Table 1 highlight the benefits of using a QHA with beam steering capabilities over using a fixed beam antenna element for a phased array antenna. For example, consider a QHA element with a fixed beam radiation pattern that has maximum gain towards 0 = 0° and = 0° direction, as in Mode 1. The gain decreases by 4.12 dBi for 0 = 40° and 11.85 dBi for 0 = 70°. A phased array antenna constructed with elements that exhibit this behaviour will have poor gain performance when steering a wide-angle beam. In contrast, a QHA antenna element with beam steering provides better gain performance for wide angle beam steering (29°). For example, the gain for Mode 2 at 0 = 40° is 7.14 dBi, which is much higher than the gain for Mode 1 at this angle. The drop in the gain for Mode 2 when the beam is steered away from the beam direction, i.e., the boresight direction, is only 0.88 dBi and 5.92 dBi for 40° and 70° steering, respectively.Table 1

[0041] Alternative simulated 3D radiation patterns for the input signal phase combinations of Mode 1, Mode 2 and Mode 3 are shown at Figure 8. Figure 8 shows a simulated 3D radiation pattern 800 A corresponding to Mode 1, a simulated 3D radiation pattern 800B corresponding to Mode 2 and a simulated 3D radiation pattern 800C corresponding to Mode 3. In Figure 8, the z- axis 802A, 802B, 802C of each of Mode 1, Mode 2 and Mode 3, respectively, defines an elevation of 0 = 0°. The simulated 3D radiation patterns of Figure 8 are based on a periodic highimpedance surface ground plane acting as an artificial magnetic conductor, such as the high impedance surface ground plane 102 described with reference to Figure 1. In the example of Figure 8, for Mode 1 the antenna is radiating in axial mode with a maximum realised gain equal to 7.49 dBi. Similarly, in Mode 2, the main beam is steered towards the direction 0 = 26° and = -73°, with a realised gain of 7.6 dBi. For Mode 3 the beam direction is almost the same as for Mode 2, however the realised gain is reduced to 6.7 dBi. Accordingly, the simulated results show that excellent performance is achievable with an antenna comprising a plurality of helical antenna elements each arranged to curve around a common longitudinal axis extending from a periodic high impedance surface ground plane acting as an artificial magnetic conductor (AMC), such as the antenna 100 described with reference to Figure 1.

[0042] In order to control the phase angle at each helical antenna element of the plurality of helical antenna elements 112, appropriate control of an input signal is used. In an example, the feeding network 116 that provides the input signals to the plurality of helical antenna elements 112 comprises a digital beamforming circuit. In a further example, the feeding network 116 comprises a plurality of power divider circuits corresponding to a plurality of different combinations of phase angles of an input signal applied to the plurality of helical antenna elements. Beneficially, each power divider is associated with a combination of phase angles that corresponds to a particular radiation pattern, thereby enabling efficient switching between particular radiation patterns without the need for more complex control circuitry.

[0043] Figure 5 shows images 500A, 500B, 500C of three power dividers. In an example, one or more of the power dividers 500A, 500B, 500C of Figure 5 are implemented in the feeding network 116 described with reference to Figure 1, in order to control the combination of different phase angles of an input applied to the plurality of helical antenna elements 112 of the antenna 100. In further examples, additional and / or alternative power dividers are implemented in the feeding network 116. A first image 500A shows a power divider 516A configured to apply the phase angles of an input signal associated with Mode 1, describe above with reference to Table 1. A second image 500B shows a power divider 516B configured to apply the phase angles of an input signal associated with Mode 2, describe above with reference to Table 1. A third image 500C shows a power divider 516C configured to apply the phase angles of an input signal associated with Mode 3, describe above with reference to Table 1. Each of the power dividers 516A, 516B, 516C has five feed ports. One port (port 1 in the case of each of the power dividers 516A, 516B, 516C) is configured to receive an input signal and controllably direct input signals to the other four ports. The variation in the path lengths of the power dividers 516A, 516B, 516C enables signals with different phase angles to be applied to each of the helical antenna elements of a quadrifilar helix antenna. For example, the power divider 516A isconfigured to receive an input signal at Port 1 and output signals to each of Ports 2 to 5, such that the output signals correspond to the input signal with phase angle differences of 90° between Port 3 and Port 2, 180° between Port 4 and Port 2 and 270° between Port 5 and Port 2. Similarly, the power divider 516B is configured to receive an input signal at Port 1 and output signals to each of Ports 2 to 5, such that the output signals correspond to the input signal with phase angle differences of 90° between Port 3 and Port 2, 90° between Port 4 and Port 2 and 180° between Port 5 and Port 2. Similarly, the power divider 516C is configured to receive an input signal at Port 1 and output signals to each of Ports 2 to 5, such that the output signals correspond to the input signal with phase angle differences of 120° between Port 3 and Port 2, 60° between Port 4 and Port 2 and 180° between Port 5 and Port 2. The performance of such power dividers 516A, 516B, 516C is analysed below, with reference to Figures 9 to 12.

[0044] Whilst particular power dividers are described with reference to Figure 5, in further examples the feeding network 116 comprises alternative and / or additional power dividers providing any suitable combination of phase angle differences of input signal to each helical antenna element of a plurality of helical antenna elements 112.

[0045] The plurality of helical antenna elements 112 is implemented in any appropriate configuration to provide the functionality described herein. For example, Figures 2A and 2B are perspective views of configurations of exemplary quadrifilar helix antennae 200A, 200B that may be implemented in the antenna 100 of Figure 1 additionally or alternatively to the plurality of helical antenna elements 112. In further examples, the plurality of helical antenna elements 112 of the antenna 100 is based on alternative and / or additional modifications of the exemplary quadrifilar helix antennae 200A, 200B of Figure 2.

[0046] Figure 2 A shows four helical antenna elements 204 A, 206 A, 208 A, 210A. In an example, the four helical elements 204 A, 206 A, 208 A, 210A correspond to the plurality of helical antenna elements 112 of the antenna 100 of Figure 1. The helical antenna elements 204A, 206A, 208 A, 210A are each arranged to curve around a common longitudinal axis extending from a planar surface 202 A. In the example of Figure 2 A, the helical antenna elements are connected together at an opposite end of the quadrifilar helix antenna 200A to the planar surface 202A to provide a short-end antenna. Figure 2B shows four helical antenna elements 204B, 206B, 208B, 210B, each arranged to curve around a common longitudinal axis extending from a planar surface 202B. In an example, the four helical elements 204B, 206B, 208B, 210B correspond to the plurality of helical antenna elements 112 of the antenna 100 of Figure 1. In contrast to the quadrifilar helix antenna 200 A of Figure 2 A, the quadrifilar helix antenna 200B of Figure 2B is shown to have an open end at the opposite end of the quadrifilar helix antenna 200B to the planar surface 202B, providing an open-end antenna.

[0047] Helical antenna antennae, such as the quadrifilar helix antenna shown at Figures 2A and 2B are optionally selected based on the functionality of the antenna, such as the functionality of the antenna 100 described with reference to Figure 1. The length and number of turns of each helical antenna element 202, 204, 206, 208 are determined based on the required frequency response and radiation pattern generated by the antenna 100 in which they are implemented. Typically, the length of each helical antenna element 202, 204, 206, 208 is an integer multiple of a quarter wavelength. For a beam of radiation generated by an antenna 100 with helical antenna elements, such as those described with reference to Figures 2A and 2B, the polarisation and beam direction mainly depend on the orientation of the helical antenna elements 204, 206, 208, 210 and the excitation phase. If the helical antenna elements 204, 206, 208, 210 are wound in the left-hand sense with clockwise phase progression of feeds, then they induce the right-hand circular polarisation wave with "forward helix mode" (radiate as an endfire beam), whereas anticlockwise phase progression induces "backward helix mode" (radiate as a backfire beam).

[0048] The antenna 100 described herein is optionally a circularly polarised antenna. The antenna 100 is optionally a right-hand circularly polarised antenna and / or a left-hand circularly polarised antenna. In an example, the feeding network 116 provides the appropriate number of input signals and configurations to enable both left-hand and right-hand circularly polarised radiation to be transmitted by the antenna 100. Whilst exemplary configurations of antenna elements are described with reference to Figure 2, in further examples, the plurality of helical antenna elements 112 of the array 100 of Figure 1 takes any appropriate configuration. For example, whilst four helical antenna elements are shown in as part of the plurality of helical antenna elements 112 arranged to curve around a longitudinal axis extending from the high impedance surface ground plane 102, in further examples the number of helical antenna elements 112 is different. In such cases, different combinations of phase angles of an input signal can be applied to the plurality of helical antenna elements such that a mode of phase angles applied to sequentially adjacent helical elements on a path around the common longitudinal axis comprises a number of phase angles that is equivalent to the number of helical antenna elements. In further examples, different combinations of phase angles of an input signal applied to a plurality of helical elements are selectively applied such that any combination of helical antenna elements receives an input signal at a given time and with a given combination of phase angles, which may include the same or different phase angle of input signal being applied to different helical antenna elements of the plurality of helical antenna elements.

[0049] The antenna 100 described herein is a transmitting antenna that is configured to transmit power. In an example, the antenna 100 described herein is configured to transmit power of at least 1 W. In further examples, the antenna 100 described herein is configured to transmit powerof at least 10 W. In further examples, the antenna 100 described herein is configured to transmit power of at least 100 W. In further examples, the antenna 100 described herein is configured to transmit power of at least 1 kW. In further examples, the antenna 100 described herein is configured to transmit power of at least IM W. In further examples, the antenna 100 described herein is configured to transmit power of at least 1 GW.

[0050] Advantageously, in an example, the antenna 100 described herein is implemented in a vector phased array comprising a controller and a plurality of antennae 100. In such a vector phased array, the antenna 100 forms a unit of the array. A vector phased array of such antenna units 100 can be steered in order to control the direction and power of a transmitted beam. Beneficially, the selection of appropriate combinations of phase angles of an input signal applied to the plurality of helical antenna elements of an antenna forming the unit of a vector phased array enables improved performance of the vector phased array, which can be dynamically adjusted in order to maintain improved performance at different angles by changing the combinations of phase angles of input signal applied to the pattern reconfigurable units 100 of the phase array in response to steering the main beam of the vector phase array.

[0051] Figure 6 shows a schematic of a wireless power transfer system 600 comprising a rectenna and one or more antennae and / or a vector phased array. In an example, the wireless power transfer system 600 comprises a plurality of the antennae 100 described with reference to Figure 1. In an example, the wireless power transfer system 600 comprises a vector phased array comprising one or more of the antennae 100 described with reference to Figure 1 in combination with a controller to directed a beam transmitted by the vector phased array. There is shown an antenna array 602 with a plurality of antennae 604. The antennae 604 correspond to a plurality of pattern reconfigurable antennae described above with reference to Figures 1 to 5. Whilst an array of antennae 604 with a number of antennae 604 is shown, in further examples the array 602 has one or more antennae 604 of any number and arranged in any appropriate configuration. Whilst a side view of the array 602 is shown, it will be understood that the array 602 may be arranged in any appropriate configuration such that the antennae 604 are spatially distributed in one, two and / or three dimensions.

[0052] Figure 15A shows a plan view of an example of a uniform planar spatially distributed array 602 having antennae 604 corresponding to a plurality of pattern reconfigurable antennae described above with reference to Figures 1 to 6. The uniform planar spatially distributed array 602 has the plurality of antennae 604 arranged in a two dimensional grid pattern on a planar surface. The uniform planar spatially distributed array may exhibit a strong mutual coupling effect when the antennae 604 are spaced closely together. This mutual coupling may cause theperformance of one antenna 604 to be influenced by the presence of the other nearby antennae 604, resulting in changes in impedance, radiation pattern, and efficiency.

[0053] Using a sparse (pseudo) random phased array 652, as shown in Figure 15B, instead of a uniform planar spatially distributed array 602 is an effective technique to reduce mutual coupling in antenna systems, particularly in phased arrays. In such a sparse (pseudo) random phased array 652, the antennae 654 are placed at random or irregular intervals rather than in a regular grid pattern. This approach helps mitigate mutual coupling effects. The arrangement of the antennae 654 in the sparse (pseudo) random phased array 652 may arise from an optimisation process to determine minimum peak sidelobe level (SLL) when the main beam is not steered, optionally taking into account peak SLL when the beam is steered. The optimisation process may be, for example, an evolutionary algorithm such as the genetic algorithm (GA), particle swarm optimization (PSO) and covariance matrix adaption evolutionary strategy (CMA-ES).

[0054] The array 602 is in communication with a further device 608 via a communication path 606. The further device 608 comprises elements for providing any necessary functionality of directing and / or generating signals to be transmitted by the antenna array 602. There is also shown a rectenna array 612 that has a receiving antenna 610 that is configured to communicate received signals to a further device 616 via a communication path 614. Whilst one receiving antenna 610 is shown, in further examples there is any appropriate number of receiving antennae 610. The further device 616 and / or rectenna array 612 includes elements for providing functionality for receiving signals from the transmitting array antenna 602 and converting the signals into an appropriate form for subsequent functionality. For example, the wireless power transfer system may be configured to transmit microwave radiation from the transmitting antenna array 602 to the rectenna array 612, which in turn converts the microwave radiation to an electrical DC signal. In further examples the wireless power transfer system 600 comprises additional and / or alternative devices for controlling and implementing the power transfer from one location to a different location. Whilst the power transfer system 600 of Figure 6 shows one transmitting antenna array 602 and one rectenna array 612, in further examples the power transfer system 600 comprises one or more further transmitting antenna array and / or receiving antenna arrays. In an example, the antenna array 602 is a vector phased array and the further device 608 is a controller and the plurality of antennae 604 is a plurality of the antenna 100 described herein.

[0055] In an example, one or more antennae 100 and / or the vector phased array comprising the antenna 100 are mounted on a satellite. For example, the transmitting antenna array 602 described with reference to Figure 6 is mounted on a satellite. In further examples, the transmitting antenna array 602 is mounted in any suitable location for transmitting power.Beneficially, when the transmitting antenna array 602 is mounted on a satellite, the use of one or more pattern reconfigurable antennae 100 as described herein enables improved power transmission over large distances. Beneficially, the wireless power transfer system 600 comprises one or more antennae 100 and / or the vector phased array configured to transmit power of at least 1 W, optionally at least 10 W, optionally at least 100 W, optionally at least 1 kW, optionally at least 1 MW, optionally at least 1 GW.

[0056] The wireless power transfer system 600 is used to transfer power by determining a beam direction based on the location of the rectenna 612 with respect to one or more antennae and or a vector phased array, selecting a combination of phase angles on an input signal from the plurality of different combinations based on the beam direction, applying the combination of phase angles of an input signal to the plurality of helical antenna elements, thereby to enable an improvement in gain optimisation associated with the beam direction and transmitting power from one or more antennae and / or the vector phase array to the rectenna 612.

[0057] As described herein, an antenna comprising a plurality of helical antenna elements each arranged to curve around a common longitudinal axis extending from a high impedance surface ground plane can be configured such that a feeding network of the antenna can apply a plurality of different combinations of phase angles of an input signal to the plurality of helical antenna elements, thereby to enable the formation of a plurality of different radiation patterns. As described above, in an example, a plurality of different combinations of phase angles of an input signal comprises: a first mode, Mode 1, wherein the phase angles applied to sequentially adjacent helical elements on a path around the longitudinal axis are: 0°, 90°, 180° and 270°. In a further example, a plurality of different combinations of phase angles of an input signal comprises: a second mode, Mode 2, wherein the phase angles applied to sequentially adjacent helical elements on a path around the longitudinal axis are: 0°, 90°, 90° and 180°. In a further example, a plurality of different combinations of phase angles of an input signal comprises: a third mode, Mode 3, wherein the phase angles applied to sequentially adjacent helical elements on a path around the longitudinal axis are: 0°, 120°, 60° and 180°. Where the phase angles of each of Mode 1, Mode 2 and Mode 3 are provided by a feeding network comprising a power divider, the different modes are selectable in order to alter the radiation pattern of the antenna. The performance of exemplary power dividers 516A, 516B, 516C, described with reference to Figure 5 and which provide input signal phase combinations corresponding to Model, Mode 2 and Mode 3, is set out here. In order to examine the performance of the power dividers 516A, 516B, 516C, the input port, port 1, of each of the power dividers 516A, 516B, 516C is connected to a vector network analyser and output ports 2 to 5 are each connected to a respective helical antenna element of a plurality of helical antenna elements.

[0058] Figure 9 shows plots of measured results for Mode 1. There is shown a plot 900A of S- parameters along the y-axis 904A as a function of frequency along the x-axis 902A and a plot 900B of phase differences along the y-axis 904B versus frequency along the x-axis 902B for the power divider 516A for Mode 1. The plot 900 A of S-parameters shows a plot of a trace 906 A where it can be observed that the reflection coefficient is below -17.5 dB at 5.8 GHz, and the output magnitudes at Ports 2-5 are similar to each other as indicated by 908A. The insertion loss is below 1.5 dB across a wide impedance bandwidth. The plot 900B of phase differences of these four ports shows that the other three ports (Ports 3-5) have around phase differences of 90° shown by a first plot 906B, 180° shown by a second plot 908B, and 270° shown by a third plot 910B, respectively. Therefore, this feeding network fully meets the design requirements for Mode 1.

[0059] Figure 10 shows plots of measured results for Mode 2. There is shown a plot 1000A of S-parameters along the y-axis 1004A as a function of frequency along the x-axis 1002A and a plot 900B of phase differences along the y-axis 1004B versus frequency along the x-axis 1002B for the power divider 516B for Mode 2. The plot 1000A of S-parameters shows a plot of a trace 1006A showing the reflection coefficient, and the output magnitudes at Ports 2-5 are similar to each other as indicated by 1008 A. The plot 1000B of phase differences of these four ports shows that the other three ports (Ports 3-5) have around phase differences of 90° shown by a two plots 1006B and 180° shown by a third plot 1008B, respectively. Similarly, this feeding network fully meets the design requirements for Mode 2.

[0060] Figure 11 shows plots of measured results for Mode 3. There is shown a plot 1100A of S-parameters along the y-axis 1104A as a function of frequency along the x-axis 1102A and a plot 1100B of phase differences along the y-axis 1104B versus frequency along the x-axis 1102B for the power divider 516C for Mode 3. The plot 1100 A of S-parameters shows a plot of a trace 1106A showing the reflection coefficient, and the output magnitudes at Ports 2-5 are similar to each other as indicated by 1108 A. The plot 1000B of phase differences of these four ports shows that the other three ports (Ports 3-5) have around phase differences of 120° shown by a first plot 1008B, 60° shown by a second plot 1106B and 180° shown by a third plot 1100B, respectively. Similarly, this feeding network fully meets the design requirements for Mode 3.

[0061] Figure 12 shows measured |Sn| results for combinations of power dividers 516A, 516B, 516C corresponding to each of Modes 1, Mode 2 and Mode 3 respectively, for an antenna, such as the antenna 100 described with reference to Figure 1. A first plot 1200A corresponding to the power divider 516A configured to generate the plurality of different phase angles of input signal of Mode 1 shows a trace 1206A of the |Sn | measurement along the y-axis 1204A as a function of frequency along the x-axis 1202A. A second plot 1200B corresponding to the power divider516B configured to generate the plurality of different phase angles of input signal of Mode 2 shows a trace 1206B of the |S n | measurement along the y-axis 1204B as a function of frequency along the x-axis 1202B.

[0062] A third plot 1200C corresponding to the power divider 516C configured to generate the plurality of different phase angles of input signal of Mode 3 shows a trace 1206C of the |Sn| measurement along the y-axis 1204C as a function of frequency along the x-axis 1202C. As can be observed, the antenna 100 can achieve good impedance matching across a relatively wide bandwidth under different operating modes. At the target 5.8 GHz frequency, the reflection coefficient is below -20 dB when using power dividers 516A and 516B corresponding to Mode 1 and Mode 2 respectively. When connecting power divider 516C corresponding to Mode 3, the reflection coefficient is below -14 dB.

[0063] Figure 13 shows plots 1300 A, 1300B, 1300C illustrating simulated 1302 A, 1302B, 1302C and measured 1304A, 1304B, 1304C far-field radiation patterns for each of Mode 1, Mode 2 and Mode 3, respectively. In each case, good agreement is achieved between the simulated results 1302A, 1302B, 1302C and respective measured results 1304A, 1304B, 1304C. As shown in a first plot 1300 A corresponding to Mode 1, the antenna 100 working in Mode 1 has a broadside radiation pattern. The measured radiation pattern 1304A is slightly asymmetrical due to the assembly and measurement errors. The radiation patterns of Mode 2 shown in a second plot 13006 shows when changing the input phases of each QHA element, a steerable beam can be realised. According to the measured result 1304B, the main beam is steered towards theta = 26°, phi = -70° direction with 6.73 dBi realised gain. The half power beam width (HPBW) for Mode 2 is 39.5°. For Mode 3, shown in a third plot 1300C of Figure 13, the main beam is steered towards the theta = 30.5°, phi = -70° direction. However, the realised gain is reduced to 4.41 dBi. The HPBW for mode 3 is 44.84° while sidelobe level (SLL) becomes higher.Table 2

[0064] Table 2 shows the comparison between data from the simulated 1302A, 1302B, 1302C and measured 1304 A, 1304B, 1304C radiation patterns for the different modes, Mode 1, Mode 2 and Mode 3. Whilst the measured gain results are slightly lower than the simulated ones, themeasured and simulated patterns exhibit a strong agreement, showing how steerable radiation patterns are formed with the antenna 100 through adjustment of the feeding phases.

[0065] Whilst the antenna 100 described herein has been verified in simulation and experiment using feeding networks 116 comprising power dividers 516A, 516B, 516C, in further examples the antenna 100 is steerable in an upper half space by controlling the input phases to the feed ports of the helical antenna elements of the plurality of helical antenna elements 112 by means of a digital beam forming circuit, thereby providing further degrees of freedom in the control of input phases to an antenna.

[0066] Whilst different combinations of phase angles are described herein with reference to Mode 1, Mode 2 and Mode 3, in further examples any appropriate combination of different combinations of phase angles of an input signal are applied to the plurality of helical antenna elements of an antenna described herein to provide improved transmission. In an example, at least one combination of the plurality of different combinations of phase angles of an input signal comprises a difference in phase angle applied to two of the helical antenna elements of: 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300° and / or 330°.

[0067] Advantageously, the antenna 100 described herein is operable to provide different functionality. In an example, a method of operating the antenna 100 comprises determining a beam direction, selecting a combination of phase angles of an input signal from the plurality of different combinations based on the beam direction; and applying the combination of phase angles of an input signal to the plurality of helical antenna elements, thereby to enable optimisation of gain associated with the beam direction. The antenna 100 is controllable such that the method further comprises varying the relative phase of the input signal at each of the plurality of helical antenna elements 112 and optionally transmitting power in the beam direction.

[0068] Alternatively, or additionally, the antenna 100 is operable to provide a method of sequentially applying different combinations of the plurality of different combinations of phase angles of an input signal to the plurality of helical antenna elements, subsequently transmitting a signal and detecting a response to the transmitted signal associated with one of the plurality of different combinations of phase angles of an input. Further, the antenna 100 is operable such that the method comprises varying the relative phase of the input signal at each of the plurality of helical antenna elements and subsequently, using the detected response to identify an object associated with the detected response.

[0069] Advantageously, the antenna 100 and / or a vector phased array of antennae, such as the antenna 100 described herein, can be mounted on a satellite. A satellite comprising such an antenna 100, or vector phased array of antenna 100 provides improved transmission of signalsover great distances. Advantageously, where the transmitted radiation is circularly polarised and the appropriate mode of operation of combination of phase angles of an input signal applied to the plurality of helical antenna elements 112 of each antenna 100, improved BCE is achieved through improved control of the direction of the beam.

[0070] The present application claims priority from GB patent application 2403085.0 filed 4March 2024, the entire contents of which are hereby incorporated by reference.

[0071] While the present invention has been described in connection with various exemplary embodiments, other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS:

1. An antenna comprising: a high impedance surface ground plane; a plurality of antenna elements each arranged to curve around a common longitudinal axis extending from the high impedance surface ground plane; and a feeding network configured to apply a plurality of different combinations of phase angles of an input signal to the plurality of antenna elements, thereby to enable the formation of a plurality of different radiation patterns.

2. The antenna according to claim 1, wherein the antenna elements are helical antenna elements extending from the high impedance surface ground plane in the direction of the common longitudinal axis.

3. The antenna according to claim 2, wherein the helical antenna elements are formed on the surface of a cylindrical member.

4. The antenna according to claim 1, wherein the antenna elements are spiral antenna elements substantially flat to the high impedance surface ground plane.

5. The antenna according to any of claims 1 to 4, wherein the feeding network is further configured to apply different relative phases of the input signal to at least two of the plurality of antenna elements.

6. The antenna according to any preceding claim, wherein the feeding network comprises a digital beamforming circuit.

7. The antenna according to any of claims 1 to 5, wherein the feeding network comprises a plurality of power divider circuits corresponding to the plurality of different combinations of phase angles of an input signal applied to the plurality of antenna elements.

8. The antenna according to any preceding claim, wherein the antenna is a circularly polarised antenna, optionally wherein the antenna is a right-hand circularly polarised antenna and / or a left-hand circularly polarised antenna.

9. The antenna according to any preceding claim, wherein at least one combination of the plurality of different combinations of phase angles of an input signal comprises a difference in phase angle applied to two of the antenna elements of: 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300° and / or 330°.

10. The antenna according to any preceding claim, wherein the antenna is a quadrifilar helix antenna comprising four antenna elements.

11. The antenna according to claim 10, wherein the plurality of different combinations of phase angles of an input signal comprises: a first mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 90°, 180° and 270°; and / or a second mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 90°, 90° and 180°; and / or a third mode wherein the phase angles applied to sequentially adjacent elements on a path around the longitudinal axis are: 0°, 120°, 60° and 180°.

12. The antenna according to any preceding claim, wherein the high impedance surface ground plane is an artificial magnetic conductor ground plane comprising a plurality of electrically conductive regions formed on a surface of a dielectric substrate.

13. The antenna according to claim 12, wherein each electrically conductive region of the plurality of electrically conductive regions is in electrical communication with an electrically conductive common plane on an opposite surface of the dielectric substrate to the plurality of electrically conductive regions.

14. The antenna according to claim 12 or claim 13, wherein the plurality of electrically conductive regions is arranged in an array having an array pitch corresponding to an operating frequency of the antenna.

15. The antenna according to any preceding claim, wherein the antenna is configured to transmit power, optionally wherein the transmitted power is at least 1 W, optionally wherein the transmitted power is at least 10 W, optionally wherein the transmitted power is at least 100 W, optionally wherein the transmitted power is at least 1 kW, optionally wherein the transmitted power is at least 1 MW, optionally wherein the transmitted power is at least 1 GW.

16. The antenna according to any preceding claim, wherein the plurality of antenna elements are metal elements printed on a flexible film.

17. A vector phased array comprising a controller and a plurality of antennae according to any of claims 1 to 16.

18. The vector phased array of claim 17, wherein the antennae are arranged at random or irregular intervals, optionally arranged as a result of an optimisation process.

19. A wireless power transfer system comprising: a rectenna; and one or more antennae according to any of claims 1 to 16, and / or the vector phased array according to claim 17 or 18.

20. The wireless power transfer system according to claim 19, wherein the one or more antennae and / or the vector phased array are mounted on a satellite.

21. The wireless power transfer system according to claim 19 or claim 20, wherein the one or more antennae and / or the vector phased array are configured to transmit power of at least 1 W, optionally at least 10 W, optionally at least 100 W, optionally at least 1 kW, optionally at least 1 MW, optionally at least 1 GW.

22. A method of operating the antenna according to any of claims 1 to 16, the method comprising: determining a beam direction; selecting a combination of phase angles of an input signal from the plurality of different combinations based on the beam direction; and applying the combination of phase angles of an input signal to the plurality of antenna elements, thereby to enable optimisation of gain associated with the beam direction.

23. The method according to claim 22, further comprising: varying the relative phase of the input signal at each of the plurality of antenna elements.

24. The method according to claim 22 or claim 23, further comprising: transmitting power in the beam direction.

25. A method of operating the antenna according to any of claims 1 to 16, the method comprising: sequentially applying different combinations of the plurality of different combinations of phase angles of an input signal to the plurality of antenna elements; and transmitting a signal and detecting a response to the transmitted signal associated with one of the plurality of different combinations of phase angles of an input.

26. The method according to claim 25, further comprising: varying the relative phase of the input signal at each of the plurality of antenna elements.

27. The method according to claim 25 or claim 26, further comprising: using the detected response to identify an object associated with the detected response.

28. A method of wirelessly transferring power using the system according to any of claims15 to 17, the method comprising: determining a beam direction based on the location of the rectenna with respect to the one or more antennae and / or vector phased array; selecting a combination of phase angles of an input signal from the plurality of different combinations based on the beam direction; applying the combination of phase angles of an input signal to the plurality of antenna elements, thereby to enable an improvement in gain optimisation associated with the beam direction; and transmitting power from the one or more antennae and / or the vector phased array to the rectenna.

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