Antenna and antenna array

Abstract

An antenna for a phased antenna array includes a conductive element, a slot provided in a conductive side of a first substrate attached to a first side of the conductive element, a radio frequency (RF) input for feeding RF energy to the slot, a patch antenna for transmitting EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side of the conductive element, and a cavity extending through the conductive element and positioned between the first and second substrates. The conductive element is configured to couple the slot and the patch antenna such that EM energy received at the slot from the RF input propagates through the cavity and is emitted as EM waves by the patch antenna.

Description

[0001] ANTENNA AND ANTENNA ARRAY

[0002] Field

[0003] The present disclosure relates to wireless communications and in particular to an antenna and an antenna array for transmitting and receiving electromagnetic waves.

[0004] Background

[0005] SAR is a type of imaging technology that can be used for a variety of applications such as Earth observation, mapping, object tracking, change detection (e.g., in glaciers), natural catastrophe monitoring, and many others. SAR images are a type of image created by transmitting radar pulses, receiving the reflected and scattered return echoes, and processing the return echoes in order to form the image. This is in contrast to optical imagery, a passive technology wherein images are captured by receiving light reflected or originating from an object. SAR technology, on the other hand, is an active rather than a passive technology since it relies on transmitting radar pulses instead of relying on sunlight or other light sources. A significant advantage of SAR technology over optical imagery is that SAR technology can image at night as well as through clouds and other adverse weather conditions. However, forming an image using SAR technology is generally more complex and requires significant signal processing of the returned echoes in order to generate the image.

[0006] More particularly, SAR images are acquired from a moving transceiver, such as a transceiver that comprises part of a satellite or a high-altitude aircraft. In a conventional imaging radar, meaning a real aperture radar without pulse compression, the spatial resolution of an image generated by measuring reflections of a radar signal is directly proportional to the time duration of the transmitted radar pulse and inversely proportional to the along-track dimension of the antenna used to transmit and receive the radar signal. In other words, the longer the antenna, the finer the along-track resolution. This means that the length of the antenna that would be required to capture high-resolution images using conventional radar is often impractical, particularly for airborne use.

[0007] In contrast, SAR images are captured using a “synthetic aperture”. A smaller and consequently more practical antenna is used on a moving platform to make a series of measurements of reflected radar signals, and those measurements are combined to simulate a much larger antenna. This is achieved by exploiting the Doppler effect created by the moving SAR platform. Consequently, the resolution of a SAR image corresponds to the resolution of a conventional radar image captured using an antenna much longer than the one used to capture the SAR image.

[0008] Various types of antennas are used for SAR applications. For example, parabolic antennas have a high gain and the ability to generate narrower beams with lower side beams. However, their relatively large size and weight have a large negative impact when the antennas are deployed on airborne / spaceborne platforms. Passive plane antennas are simpler to manufacture and cheaper, although their beamwidth is wider, and they lack the ability to be steered. Active phased array antennas, on the other hand, have the same capabilities as passive plane antennas, but benefit from beam steering and narrower beamwidths, at the cost of increased complexity.

[0009] Summary

[0010] According to a first aspect of the disclosure, there is provided an antenna for a phased antenna array, comprising: a conductive element; a slot provided in a conductive side of a first substrate attached to a first side of the conductive element; a radio frequency (RF) input for feeding RF energy to the slot; a patch antenna for transmitting EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side of the conductive element; and a cavity extending through the conductive element and positioned between the first and second substrates, wherein the conductive element is configured to couple the slot and the patch antenna such that EM energy received at the slot from the RF input propagates through the cavity and is emitted as EM waves by the patch antenna.

[0011] At least one of the first and second substrates may be flexible.

[0012] At least one of the first and second substrates may be a printed circuit board (PCB).

[0013] The conductive side of the first substrate may face toward the cavity.

[0014] The patch antenna may be provided on a side of the second substrate that faces away from the cavity.

[0015] The side of the second substrate that faces away from the cavity may be conductive, and the second substrate may further comprise a side that faces the cavity and that is non- conductive. The conductive element may be rigid.

[0016] The EM waves may be in one or more of the X-band, the C-band, the L-band, and the Ka- band.

[0017] The conductive side of the first substrate, and the patch antenna, may be coated with a material to prevent oxidation.

[0018] The first substrate may further comprise a second side that faces away from the cavity and on which is formed an RF feed that extends in a direction perpendicular to the direction in which the slot extends.

[0019] The RF feed may comprise a feed stub at an end thereof, and the feed stub may extend past the slot.

[0020] According to a further aspect of the disclosure, there is provided an antenna for a phased antenna array, comprising: a conductive element; a slot provided in a conductive side of a first substrate attached to a first side of the conductive element; a radio frequency (RF) output for receiving RF energy from the slot; a patch antenna for receiving EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side of the conductive element; and a cavity extending through the conductive element and positioned between the first and second substrates, wherein the conductive element is configured to couple the slot and the patch antenna such that EM waves received at the patch antenna propagate through the cavity and are received as EM energy at the RF output from the slot.

[0021] According to a further aspect of the disclosure, there is provided a phased antenna array comprising: multiple antennas, each antenna in accordance with any of the abovedescribed antennas; one or more radio frequency (RF) sources for generating one or more RF signals to be delivered to each RF input; and one or more controllers configured to control the one or more RF sources to control an RF beam generated by the antennas as a result of the EM waves emitted by each patch antenna.

[0022] Each first substrate may be part of a first common substrate. Each second substrate may be part of a second common substrate. Each conductive element may be part of a common conductive grid through which each cavity extends. According to a further aspect of the disclosure, there is provided a synthetic aperture radar (SAR) imaging system comprising a phased antenna array according to any of the abovedescribed phase antenna arrays.

[0023] According to a further aspect of the disclosure, there is provided a spaceborne or airborne platform comprising a phased antenna array according to any of the above-described phase antenna arrays and configured to perform synthetic aperture radar (SAR) imaging.

[0024] According to a further aspect of the disclosure, there is provided a method of performing synthetic aperture radar (SAR) imaging, comprising: flying a spaceborne or airborne platform over a target location on the Earth’s surface, wherein the spaceborne or airborne platform comprises a phased antenna array according to any of the above-described phased antenna arrays, and wherein the phased antenna array is configured to perform synthetic aperture radar (SAR) imaging; and performing SAR imaging of the target location using the phased antenna array.

[0025] This summary does not necessarily describe the entire scope of all aspects. Other aspects, features, and advantages will be apparent to those of ordinary skill in the art upon review of the following description of specific embodiments.

[0026] Drawings

[0027] Embodiments of the disclosure will now be described in detail in conjunction with the accompanying drawings of which:

[0028] FIG. 1 is a schematic diagram of a SAR satellite orbiting the Earth, according to an embodiment of the disclosure;

[0029] FIG. 2 is a schematic diagram of a ground station relaying SAR image data from a SAR satellite to a SAR processing station, according to an embodiment of the disclosure;

[0030] FIG. 3 is a schematic diagram of a computing device configured to process and generate SAR image data, according to an embodiment of the disclosure;

[0031] FIG. 4 is a first perspective view of an antenna for a phased antenna array, according to an embodiment of the disclosure;

[0032] FIG. 5 is a second perspective view of the antenna of FIG. 4, according to an embodiment of the disclosure; FIG. 6 is a first cross-sectional view of the antenna of FIG. 4, according to an embodiment of the disclosure;

[0033] FIGS. 7A and 7B are further cross-sectional views of the antenna of FIG. 4, according to an embodiment of the disclosure;

[0034] FIG. 8 is a first perspective view of a phased antenna array according to an embodiment of the disclosure;

[0035] FIG. 9 is a second perspective view of the phased antenna array of FIG. 8, according to an embodiment of the disclosure;

[0036] FIG. 10 is a perspective view of a conductive grid of the phased antenna array of FIG. 8, according to an embodiment of the disclosure;

[0037] FIG. 11 is a plot of simulated electric field distribution using the antenna of FIG. 4, according to an embodiment of the disclosure;

[0038] FIG. 12 is a plot of simulated far-field electric field distribution using the antenna of FIG. 4 at 9.2 GHz, according to an embodiment of the disclosure;

[0039] FIG. 13 is a plot of simulated far-field electric field distribution using the antenna of FIG. 4 at 9.65 GHz, according to an embodiment of the disclosure;

[0040] FIG. 14 is a plot of simulated far-field electric field distribution using the antenna of FIG. 4 at 10.4 GHz, according to an embodiment of the disclosure;

[0041] FIG. 15 is a plot of a simulated Sn parameter using the antenna of FIG. 4, according to an embodiment of the disclosure;

[0042] FIG. 16 is a plot of a measured Sn parameter using the antenna of FIG. 4, according to an embodiment of the disclosure;

[0043] FIG. 17 is a third perspective view of the antenna of FIG. 4, according to an embodiment of the disclosure;

[0044] FIG. 18 is a fourth perspective view of the antenna of FIG. 4, according to an embodiment of the disclosure;

[0045] FIG. 19 is a third cross-sectional view of the antenna of FIG. 4, according to an embodiment of the disclosure; and FIG. 20 is a cross-sectional view of an antenna for a phased antenna array, according to an embodiment of the disclosure.

[0046] Detailed Description

[0047] The present disclosure seeks to provide a novel antenna and a novel antenna array (such as a phased antenna array) comprising multiple such antennas. While various embodiments of the disclosure are described below, the disclosure is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the disclosure which is to be limited only by the appended claims.

[0048] Generally, according to embodiments of the disclosure, there is provided an antenna that may be used, for example, in a phased antenna array. The antenna (or “antenna element”, when referring to one such antenna in an array of such antennas) comprises a conductive element, a slot provided in a conductive side of a first substrate attached to a first side of the conductive element, a radio frequency (RF) input for feeding RF energy to the slot, a patch antenna for transmitting EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side, and a cavity extending through the conductive element and positioned between the first and second substrates. The conductive element is configured to couple the slot and the patch antenna such that EM energy received at the slot from the RF input propagates through the cavity and is emitted as EM waves by the patch antenna. Such an antenna may be used to transmit EM waves (i.e. , act as a transmitter), but may equally well be used to receive EM waves (i.e., act as a receiver), in which case the RF input acts as an RF output and the conductive element is configured to couple the slot and the patch antenna such that EM waves received at the patch antenna propagate through the cavity and are received as EM energy at an RF output from the slot.

[0049] According to some embodiments, the antenna may have a bandwidth of about 2.11 GHz. According to some embodiments, the antenna may have an injection loss of less than -20 dB from 9.2 GHz to 10.4 GHz. According to some embodiments, the antenna may have a mismatch loss of <= 0.04 dB.

[0050] The conductive element may be rigid in which case the conductive element may render the antenna more structurally sound. According to some embodiments, the conductive element may be formed of any material that is conductive to RF energy, including but not limited to aluminium and carbon fiber. Ideally, the material should be lightweight. According to some embodiments, the conductive element may be wholly conductive or may comprise a first material that is coated with a second material that is RF-conductive. Furthermore, the pair of substrates need not be directly connected which may increase the immunity of the antenna to electrostatic discharge.

[0051] According to some embodiments, air or a vacuum is used as the dielectric within the cavity. When multiple such antennas are incorporated to form a phased antenna array, the conductive element of each antenna may form part of a single “honeycomb” structure or grid, an example of which can be seen in FIG. 10. The conductive grid may improve isolation between elements of the antennas and may improve the maximum scanning angle of the phased array.

[0052] The antenna and phased antenna array described herein may be used in synthetic aperture radar (SAR) applications, and for example may be mounted on a satellite orbiting the Earth (for example, in a Low Earth Orbit) for use in SAR imaging.

[0053] FIG. 1 depicts an exemplary satellite 100 in orbit around the Earth of the kind which may include a phased antenna array as described herein. Satellite 100 comprises a body 110 which may be referred to in the art as a “bus” since it may house or support so-called bus components of a satellite. Body 110 may additionally house one or more batteries. Body 110 may be partially enclosed, for example to house and protect components. A housing may provide surfaces on which components may be mounted. In the example of FIG. 1 , a solar panel is mounted on one rectangular surface of body 110 and additional solar panels 150 may be attached to this solar panel by struts.

[0054] Satellite 100 comprises a radar antenna array 160 in the form of a generally planar structure extending from bus 110 in two opposing directions to provide two “wings”. The structure comprising wings 160 is shown to be mounted on or adjacent to a rectangular surface of body 110. Body 110 and wings 160 of satellite 100 may be collectively referred to as the spacecraft frame. Antenna array 160 together with associated amplifiers and a power distribution system (not shown) collectively form an image acquisition apparatus of satellite 100. Radar antenna array 160 may comprise a phased antenna array as described herein.

[0055] As described above, in a synthetic aperture radar system (SAR system), antenna array 160 is operated to transmit radar signals to the Earth and receive returning echoes or reflections of these signals. By recording the echoes, an image of the Earth’s surface can be constructed from the data, including the length of time taken for the echo to return (indicating location), the amplitude of the radar return, and the phase information that is included within the radar return. Further location information is obtained from the frequency of the radar return which is shifted due to the Doppler effect as a result of the motion of satellite 100 relative to the Earth.

[0056] Satellite 100 is provided with a propulsion system 190 for manoeuvring satellite 100 with a generated thrust. Propulsion system 190 comprises a plurality of thrusters 192, 194, 196, 198 that produce thrust for manoeuvring satellite 100 when required, for example to position satellite 100 onto a different orbital track. Thrusters 192, 194, 196, 198 shown in FIG. 1 are positioned at the comers of one side of body 110 and may be equally spaced apart. However, in other embodiments, propulsion system 190 may have a different configuration.

[0057] In some embodiments, satellite 100 may be orbiting Earth in a low-earth orbit. A low-earth orbit may have an altitude between 160 kilometres and 1 ,000 kilometres above the surface of the Earth. Examples of Earth-observation satellites operating SAR payloads can accordingly have orbits with an altitude of between 450 kilometres and 650 kilometres above the Earth. In one particular example, a SAR satellite may have an orbit that is approximately 550 kilometres above the Earth’s surface. At an orbit of 550 kilometres above the Earth, the satellite may be effectively traversing the ground at approximately 7.5 kilometres per second, or 27,000 kilometres per hour. Most satellites in such an orbit will traverse the Earth at a speed that is in the range of 7-8 kilometres per second.

[0058] As a SAR satellite operates its SAR payload and receives radar returns, it accumulates raw “SAR data”. Raw SAR data generally comprises the recorded radar signals as they are received by the SAR sensor. These signals are typically represented as complex-valued numbers, where each complex value consists of two components: the in-phase (I) component and the quadrature (Q) component. SAR data is typically received and processed in I and Q channels, and therefore it is traditional to represent SAR data in this form. These components correspond to the real and imaginary parts of the complex number and contain the information necessary to derive the amplitude and phase of the received radar signal. In order to construct an image corresponding to the SAR data, the data must be processed. While in theory the data may be processed by any suitable computer processor, even a computer processor onboard the satellite, it is more typical for the raw SAR data to be first transmitted or downlinked from the SAR satellite to a ground station on the Earth’s surface. The data can be downlinked whenever the SAR satellite has line of sight to the ground station. The downlinked SAR data is then typically relayed to a SAR processing station which performs the necessary processing of the SAR data, as now described in further detail.

[0059] In particular, referring to FIG. 2, there is shown a schematic diagram of hardware components onboard satellite 100 being used to allow satellite 100 to communicate with a SAR processing station 20 on the Earth’s surface. SAR processing station 20 houses the computer hardware components that are used to process the SAR data and generate the SAR images. Typically, satellite 100 will first downlink the SAR data to a ground station 39, and ground station 39 will relay (using a wired or wireless communication link) the downlinked SAR data to SAR processing station 20. However, it is possible, according to some embodiments, for ground station 39 to process the SAR data, in which case ground station 39 effectively performs the function of SAR processing station 20. SAR processing station 20 can be an office, an operations station, or any other location comprising any computer device (such as a laptop) capable of processing the SAR data. The SAR processing may also be carried out using cloud computing, for example through the use of multiple processors operating in parallel, in which case SAR processing station 20 is the location at which the SAR data is received and passed to the cloud.

[0060] Generally, satellite 100 includes a SAR payload 16 (e.g., comprising antenna array 160), satellite processing equipment 34, and a transmitter 36. Meanwhile, SAR processing station 20 includes a receiver 22 and SAR Processing Equipment 24. Satellite processing equipment 34 and SAR Processing Equipment 24 comprise suitable computer processors, comprising circuitry, and computer-readable media configured to perform various data processing functions. Ground station 39 includes a transceiver 37 (or a separate transmitter and receiver) for relaying the SAR data from satellite 100 to SAR processing station 20. For example, relaying the SAR data from ground station 39 to SAR processing station 20 can be performed through a wired or wireless terrestrial network. According to some embodiments, if satellite 100 is not in direct communication with ground station 39, the SAR data can be relayed to ground station 39 via another satellite or an aircraft.

[0061] During operation, data captured by SAR payload 16 is passed to satellite processing equipment 34 for pre-processing (which may include, for example, basic compression / encoding / packaging). Following pre-processing, the pre-processed data is passed to transmitter 36 which transmits or otherwise downlinks the data to transceiver 37 of ground station 39. Transceiver 37 of ground station 39 then relays the SAR data to receiver 22 of SAR processing station 20. Receiver 22 passes the data to SAR Processing Equipment 24 which processes the data.

[0062] Turning to FIG. 3, there is shown an example of hardware components in SAR Processing Equipment 24. In particular, a computer system 200 comprises a processor 202 that controls computer system’s 200 overall operation. Processor 202 is communicatively coupled to and controls several subsystems. These subsystems comprise an input / output (“I / O”) controller 211 , which is communicatively coupled to user input devices 204. User input devices 204 may comprise, for example, any one or more of a keyboard, mouse, touch screen, and microphone. The subsystems further comprise random access memory (“RAM”) 206 which stores computer program code for execution at runtime by processor 202; non-volatile storage 208 which stores the computer program code executed by RAM 206 at runtime; graphical processing units (“GPU”) 212 which control a display 216; and a network interface 214 which facilitates network communications with a database 218. Nonvolatile storage 208 has stored on it computer program code that is loaded into RAM 206 at runtime and that is executable by processor 202. When the computer program code is executed by processor 202, processor 202 causes computer system 200 to generate SAR image data. Additionally or alternatively, multiple of computer systems 200 may be networked together and collectively perform that method using distributed computing.

[0063] Turning to FIG. 4, there is shown a first perspective view of an antenna 400 for a phased antenna array, according to an embodiment of the disclosure.

[0064] Antenna 400 includes a first flexible printed circuit board (PCB) 40 attached to a first side of a rigid, conductive element 46. While the rigidity of conductive element 46 lends structural integrity to antenna 400, conductive element 46 need not be rigid and according to some embodiments may be flexible instead. According to some embodiments, conductive element 46 may comprise aluminum. Antenna 400 further includes a second PCB 42 attached to an opposite, second side of conductive element 46. According to some embodiments, substrates other than PCBs may be used. According to some embodiments, the substrates need not be flexible, and may be rigid. According to some embodiments, conductive element 46 may be made of other suitably conductive metals and materials such as carbon fibre. A patch antenna 44 (or “patch 44”) is formed on one side of PCB 40 (in particular, the side facing away from conductive element 46) and is used for transmitting or receiving electromagnetic (EM) waves, as described in further detail below. Patch antenna 44 may comprise conductive copper metal and may be coated with silver oxide to prevent oxidation in space. According to some embodiments, the EM waves that may be transmitted / received by patch 44 may be between 9.2 and 10.4 GHz (in the X-band). However, as described in further detail below, various parameters of antenna 400 may be adjusted in order to tailor antenna 400 such that it may transmit / receive EM waves in other bands, such as the C-band, the L-band, and the Ka-band.

[0065] Given their flexibility, PCBs 40 and 42 may be referred to as flexible circuits (sometimes known as “flex-circuits”). According to some embodiments, PCBs 40 and 42 may comprise RF laminates formed of a woven matrix of fiberglass fabric that is coated with PTFE. For example, PCBs 40 and 42 may comprise RF laminates formed of Taconic™ TLP-5 (this material generally having good RF characteristics for wideband antenna designs (e.g., a low dielectric constant and low tangent delta)). Although the coefficient of thermal expansion of such material in the z-direction may be higher, such expansion may have a negligible impact on the overall structure of antenna 400 given the relatively low thickness of the laminate (according to one example embodiment, a thickness of 0.254 mm).

[0066] As will be made clearer below and with reference to FIGS. 7A and 7B, PCB 42 is a doublesided PCB, meaning that PCB 42 comprises a first side 42a, facing an internal cavity 43, that is conductive and into which a slot 48 has been formed, and a second side 42b, facing away from cavity 43, on which a conductive RF feed 49 has been formed as a microstrip. Slot 48 and RF feed 49 can be formed by a subtractive process, such as etching away, according to a pattern, the conductive material that is not desired, or by an additive process such as printing the conductive material onto the substrate. PCB 40 may be a single-sided or a double-sided PCB. In the case of a single-sided PCB, PCB 40 comprises a first side 40a, facing cavity 43, that is non-conductive, and a second side 40b, facing away from cavity 43, that is conductive and has been formed into patch 44. If PCB 40 starts as a double-sided PCB, the conductive material on the side facing cavity 43 (i.e., side 40a) can be removed such that side 40a is not conductive. Optionally, the conductive material 45 can be left in those places where PCB 40 attaches to conductive element 46. This can have the benefit of helping adhesion between conductive element 46 and PCB 40, but is not always necessary. The conductive surfaces of both PCBs (PCB 40 and PCB 42) can comprise copper. The conductive surfaces can also be coated with a material such as silver oxide to provide improved oxidation resistance.

[0067] Turning to FIG. 5, there is shown the other side of antenna 400. As can be seen, an RF connector 41 is coupled to RF feed 49 formed on the outward-facing side 42b of PCB 42. RF feed 49 couples EM energy to / from slot 48 (not shown in FIG. 5 but shown in FIGS. 6 and 7) formed in the conductive surface of the opposite, inward-facing side 42a of PCB 42. Slot 48 is formed in the cavity-facing conductive surface 42a of PCB 42, such that the rest of surface 42a is conductive. According to some embodiments, instead of being formed as a microstrip, RF feed 49 may comprise a stripline instead.

[0068] FIG. 6 shows a cross-sectional view of antenna 400 taken through a plane defined by conductive element 46. As can be seen, internal cavity 43 extends through conductive element 46, and is defined by side 40a of PCB 40 (not shown), side 42a of PCB 42, and by the interior walls of conductive element 46. Cavity 43 is filled with a dielectric such as air or a vacuum. As described above, slot 48 is shown formed in conductive side 42a of PCB 42. Slot 48 extends in a direction perpendicular to the direction in which RF feed 49 extends.

[0069] FIGS. 7A and 7B show different cross-sectional views of antenna 400, this time in schematic form and taken through PCB 40, conductive element 46, and PCB 42. FIG. 7B is shown not to scale, so as to emphasize in particular the RF feed, the slot, and the patch. As can be seen, patch 44 is formed (e.g., by etching or by an additive process) out of conductive side 40b of PCB 40 that faces away from cavity 43, whereas slot 48 is formed in side 42a of PCB 42 that faces toward cavity 43. RF feed 49 can be seen formed on side 42b of PCB 42 that faces away from cavity 43, and extends over slot 48. The long length of slot 48 extends in and out of the page, perpendicular to the long length of RF feed 49.

[0070] The dimensions of the components of antenna 400 are designed such that, when performing a transmitting function, EM energy received at slot 48 propagates through cavity 43 and is emitted as EM waves by patch 44. Likewise, the dimensions of the components of antenna 400 are designed such that, when performing a receiving function, EM waves received at patch 44 propagate through cavity 43 and are received as EM energy at slot 48. In this context, FIGS. 17-19 illustrate dimensions that may be used according to one specific embodiment of the disclosure. In particular, FIG. 17 shows the length and width of patch 44, as well as the length and width of one antenna element. FIG. 18 shows the length and width of slot 48 as well as the total length and width of RF feed 49. As can also be seen in FIG. 18, slot 48 extends in a direction perpendicular to the direction in which RF feed 49 extends. RF feed 49 ends in an open-ended feed stub 47 that extends past the center of slot 48 and whose dimensions are carefully chosen through simulation to maximize transfer of EM waves through slot 48 at the required frequency. As can be seen in FIG. 18, according to the example embodiment shown therein, feed stub 47 may have a length of 1.57 mm. FIG. 19 shows the length and width of cavity 43 and the thickness of conductive element 46.

[0071] Multiple such antennas 400 (or “antenna elements 400”) may be combined together to form an antenna array, an example of which is shown in FIGS. 8 and 9. As can be seen in FIG. 8, an 8x16 array of antenna elements 400 has been formed in order to implement a phased antenna array 500. Whereas FIG. 8 shows sides 40b of each antenna element 400, FIG. 9 shows sides 42b of each antenna element 400. One difference between the antenna elements 400 shown in FIG. 9 and the one described in FIGS. 4-7 is the relative positions of RF connectors 41. In particular, in the array shown in FIG. 9, each row of antenna elements 400 comprises a single RF connector 41 (or “RF input / output” 41) configured to deliver RF power I receive an RF signal to / from each of eight distinct antenna elements 400.

[0072] As can be seen in FIG. 9, a number of RF inputs / outputs 41 (depending on whether phased antenna array 500 is being used as a transmitter or a receiver) are provided on antenna array 500. Each RF input / output 41 is used to feed / receive RF energy to / from a single row of antenna elements 400. In particular, each RF input / output 41 is connected by a feed network 54 to the respective slot 48 of each antenna element 400. Feed network 54 may comprise any suitable architecture, and in the example shown in FIG. 9 includes T-junctions 55 implemented using microstrip lines. However, striplines may be used instead, for example.

[0073] When being used to perform a transmitting function, an RF signal is provided to each RF input 41 which then distributes the RF signal, via feed network 54, to each connected slot 48. The RF signal is then propagated through each cavity of each antenna element in the same row as RF input 41. The RF signal is then received at each patch of each antenna element. Each patch then causes the RF signal to be emitted as EM waves. Similarly, when performing a receiving function, EM waves are received at a patch and propagate through the cavity before being received at the associated slot. The slot then causes the received RF signal to be passed to RF output 41 , via feed network 54. Once received at RF output 41 , the RF signal can then be decoded using suitable signal processing techniques known in the art.

[0074] The RF signal that is passed to each RF input 41 can be controlled using one or more controllers (not shown) comprising circuity (such as one or more microcontrollers). In particular, any of the amplitude, phase, frequency, pulse width, duty cycle, and pulse repetition frequency may be controlled. Furthermore, controlling the phase of the RF signal provided to each RF input 41 allows for steering of the EM beam that is generated as a result of each antenna element 400 of antenna array 500 transmitting / receiving EM waves. Between the PCB substrate that forms a first side of antenna array 500 and the PCB substrate that forms a second, opposite side of antenna array 500, a conductive grid 600 is provided which provides the conductive element of each antenna element. In particular, a number of apertures 650 extend through conductive grid 600 and, when each PCB substrate is attached to each respective side of conductive grid 600, each aperture 650 forms a cavity for each antenna element 400. As described above, conductive grid 600 may be formed of a suitable conductive material such as aluminum or carbon fiber.

[0075] FIG. 20 shows another antenna element 1400 that forms part of array 500. Unlike antenna element 400, the conductive element of each antenna element 1400 includes curved portions 147 to allow for mounting holes 149 to be provided in antenna element 1400. Mounting holes 149 can be used to mount array 500 to the rest of the satellite structure. It has been found that this modification to the shape of the cavity has minimal effect on the efficacy of the antenna. However, the number of antenna elements 1400 relative to antenna elements 400 is still kept relatively low, to further limit the effect that mounting holes 149 might have on the array’s performance. Also visible in antenna elements 400 and 1400 of FIG. 20 are vent holes 81 that extend from the outside of the antenna elements into the cavities. Vent holes 81 can be useful in applications where pressure equalization is desired, and particularly in space applications to provide, after launch, a way for the air to escape into the vacuum of space. In some other applications these vent holes may not be needed. When designing the antenna shown in FIGS. 17-19, the Sn parameter was focussed on, with the objective being an injection loss of no more than -20 dB in the 9.2 GHz to 10.4 GHz bandwidth. As known in the art, the Sn parameter is a measure of the reflection coefficient at the input port of the network, and describes how much of the incident signal is reflected back from the input port due to impedance mismatches. The parameters taken into account for the optimization of the antenna were: patch width, patch height, slot width, slot height, the length of feed stub 47, and the dimensions and location of RF feed 49 relative to slot 48.

[0076] To design the antenna, simulations were carried out to determine the dimensions of the various parts of the antenna, such as the slot, the patch, and the feed, in order to optimize for minimum reflected energy and maximum forward energy. In the simulations, the interior walls of the cavity being simulated were assumed to be perfectly square in order to accelerate the design and optimization process, but the comers of the walls may be rounded to simplify fabrication of the grid shown in FIG. 10.

[0077] FIG. 11 shows a simulated electric field distribution using antenna 400, with the patch facing up on the page, and the RF feed and the slot visible below.

[0078] FIG. 12 shows a simulated far-field electric field distribution using antenna 400 at 9.2 GHz. Darker shading correlates to stronger field strength. A uniform electric field pattern emitted by the antenna can be seen, with a peak gain occurring at the top of the rounded portion equal to 7.22 dB.

[0079] FIG. 13 shows a simulated far-field electric field distribution using antenna 400 at 9.65 GHz. The emission pattern is similar to the pattern obtained at 9.2 GHz, but with a slightly higher peak gain of 7.8 dB.

[0080] FIG. 14 shows a simulated far-field electricfield distribution using antenna 400 at 10.4 GHz. The emission pattern of this example is similar to the ones at 9.2 GHz and 9.65 GHz, but with a yet higher peak gain of 8.32 dB. FIGS. 12 - 14 show that it is possible to maintain a consistent emission pattern over a given range of frequencies, with a relatively small change in gain across the frequency range. It is not surprising to have a slightly higher peak gain with higher frequency.

[0081] FIG. 15 is a plot of simulated Sn parameters (reflected energy) versus frequency using antenna 400. As known in the art, the Sn parameter is a measure of the reflection coefficient at the input port of the network, and describes how much of the incident signal is reflected back from the input port due to impedance mismatches. As can be seen in the plot of FIG. 15, the antenna displays very low reflected energy (e.g., less than -20 dB) in the frequency range of interest from about 9.2 GHz to about 10.4 GHz. When designing the antenna elements, the performances of a collection of antenna elements with different patch sizes were tested. Once the parameters of the antenna elements were finalized (as can be seen in FIGS. 17-19), an array of 8x16 antenna elements was formed (as can be seen in FIGS. 8 and 9). FIG. 16 which shows the measurements of the Sn parameters for each row of the final antenna array vs. frequency. As can be seen, the actual results also demonstrated performance with low reflected energy, staying below the -20 dB line from approximately 9.2 GHz to 10.4 GHz. In fact, even lower reflected energy (e.g., down to -50 dB) was demonstrated at certain frequencies in the actual results when compared to the simulated results in which reflected energy only went down to about -27 dB. The following operational parameters were recorded for the array.

[0082] This result illustrates an example lightweight antenna, according to the current disclosure, that exhibits relatively high forward power (99%), relatively low reflected power (1 %), and relatively low return losses and low mismatch losses.

[0083] Although examples of the antenna described herein may be beneficial for Synthetic Aperture Radar (SAR) applications on a satellite in space, the antenna could also be used in many other antenna applications, and in different frequency ranges, in which a lightweight antenna with relatively high forward power, relatively low reflected power, and relatively low return losses and low mismatch losses is desired.

[0084] The word “a” or “an” when used in conjunction with the term “comprising” or “including” in the claims and / or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one” unless the content clearly dictates otherwise. Similarly, the word “another” may mean at least a second or more unless the content clearly dictates otherwise.

[0085] The terms “coupled”, “coupling” or “connected” as used herein can have several different meanings depending on the context in which these terms are used. For example, as used herein, the terms coupled, coupling, or connected can indicate that two elements or devices are directly connected to one another or connected to one another through one or more intermediate elements or devices via a mechanical element depending on the particular context. The term “and / or” herein when used in association with a list of items means any one or more of the items comprising that list. As used herein, a reference to “about” or “approximately” a number or to being “substantially” equal to a number means being within + / - 10% of that number.

[0086] Use of language such as “at least one of X, Y, and Z,” “at least one of X, Y, or Z,” “at least one or more of X, Y, and Z,” “at least one or more of X, Y, and / or Z,” or “at least one of X, Y, and / or Z,” is intended to be inclusive of both a single item (e.g., just X, or just Y, or just

[0087] Z) and multiple items (e.g., {X and Y}, {X and Z}, {Y and Z}, or {X, Y, and Z}). The phrase “at least one of” and similar phrases are not intended to convey a requirement that each possible item must be present, although each possible item may be present.

[0088] While the disclosure has been described in connection with specific embodiments, it is to be understood that the disclosure is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the disclosure.

[0089] It is furthermore contemplated that any part of any aspect or embodiment discussed in this specification can be implemented or combined with any part of any other aspect or embodiment discussed in this specification.

Claims

Claims1 . An antenna for a phased antenna array, comprising: a conductive element; a slot provided in a conductive side of a first substrate attached to a first side of the conductive element; a radio frequency (RF) input for feeding RF energy to the slot; a patch antenna for transmitting EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side of the conductive element; and a cavity extending through the conductive element and positioned between the first and second substrates, wherein the conductive element is configured to couple the slot and the patch antenna such that EM energy received at the slot from the RF input propagates through the cavity and is emitted as EM waves by the patch antenna.

2. The antenna of claim 1 , wherein at least one of the first and second substrates is flexible.

3. The antenna of claim 1 or 2, wherein at least one of the first and second substrates is a printed circuit board (PCB).

4. The antenna of any one of claims 1 -3, wherein the conductive side of the first substrate faces toward the cavity.

5. The antenna of any one of claims 1-4, wherein the patch antenna is provided on a side of the second substrate that faces away from the cavity.

6. The antenna of claim 5, wherein the side of the second substrate that faces away from the cavity is conductive, and wherein the second substrate further comprises a side that faces the cavity and that is non-conductive.

7. The antenna of any one of claims 1 -6, wherein the conductive element is rigid.

8. The antenna of any one of claims 1 -7, wherein the EM waves are in one or more of the X-band, the C-band, the L-band, and the Ka-band.

9. The antenna of any one of claims 1 -8, wherein the conductive side of the first substrate, and the patch antenna, are coated with a material to prevent oxidation.

10. The antenna of any one of claims 1-9, wherein the first substrate further comprises a second side that faces away from the cavity and on which is formed an RF feed that extends in a direction perpendicular to the direction in which the slot extends.11 .The antenna of claim 10, wherein the RF feed comprises a feed stub at an end thereof, and wherein the feed stub extends past the slot.

12. An antenna for a phased antenna array, comprising: a conductive element; a slot provided in a conductive side of a first substrate attached to a first side of the conductive element; a radio frequency (RF) output for receiving RF energy from the slot; a patch antenna for receiving EM waves and positioned on a second substrate attached to a second side of the conductive element that is opposite the first side of the conductive element; and a cavity extending through the conductive element and positioned between the first and second substrates, wherein the conductive element is configured to couple the slot and the patch antenna such that EM waves received at the patch antenna propagate through the cavity and are received as EM energy at the RF output from the slot.

13. A phased antenna array comprising: multiple antennas, each antenna in accordance with any one of claims 1-11 ; one or more radio frequency (RF) sources for generating one or more RF signals to be delivered to each RF input; and one or more controllers configured to control the one or more RF sources to control an RF beam generated by the antennas as a result of the EM waves emitted by each patch antenna.

14. The phased antenna array of claim 13, wherein:each first substrate is part of a first common substrate; each second substrate is part of a second common substrate; and each conductive element is part of a common conductive grid through which each cavity extends.

15. A synthetic aperture radar (SAR) imaging system comprising a phased antenna array according to claim 13 or 14.

16. A spaceborne or airborne platform comprising a phased antenna array according to any one of claims 13-15 and configured to perform synthetic aperture radar (SAR) imaging.

17. A method of performing synthetic aperture radar (SAR) imaging, comprising: flying a spaceborne or airborne platform over a target location on the Earth’s surface, wherein the spaceborne or airborne platform comprises a phased antenna array according to claim 13 or 14, and wherein the phased antenna array is configured to perform synthetic aperture radar (SAR) imaging; and performing SAR imaging of the target location using the phased antenna array.

Images