Wirelessly powered antenna sensing system

Abstract

An antenna system comprising: a receiving antenna section configured to receive a wireless radio frequency signal; and a rectifier system connected to the receiving antenna section by a primary transmission line that is configured to convey the radio frequency signal received by the receiving antenna section. The rectifier system is configured to convert the received radio frequency signal into a direct current power signal. The antenna system further comprises: a processing unit configured to be powered by the direct current power signal from the rectifier system; and a coupler configured to capacitively couple a portion of the radio frequency signal conveyed by the primary transmission line for processing by the processing unit without passing through the rectifier system.

Description

[0001] WIRELESSLY POWERED ANTENNA SENSING SYSTEM

[0002] Field of the Invention

[0003] The present invention relates to an antenna system able to simultaneously process an incident signal for analysis and use the same signal to power components of the antenna system.

[0004] Background

[0005] Rectifying antennas, also known as rectennas, are used to extract direct current power from incident radio frequency (RF) plane waves. These waves may originate from ambient or dedicated sources. Rectennas have found applications across a range of industries including, for example, wearable devices such as are used in fitness tracking or healthcare monitoring that can be powered using rectified DC output from one or more rectennas. In an industrial setting, the RF power transmitter may be supplied from the mains or from another renewable energy harvesting source, such as a solar panel or a mechanical generator. The RF power can then be delivered to energy-scarce and inaccessible locations, where parameters such as temperature, strain, or vibration need to be detected continuously.

[0006] Rectennas are particularly useful because they are suitable for use in low-power contexts (e.g., powers on the scale of milliwatts), even with ranges exceeding 1 metre (the maximum useable range is typically 10 to 20 metres for a sub-GHz carrier frequency with compact antennas having complex-conjugate matched dipoles, and 20 to 40 metres for a 5.8 GHz system with directional antennas such as a lensbased or large-array-based system having gains of 20 decibels or more).

[0007] In principle, RF signals could be used to passively detect changes in the surroundings of sensing antennas through changes in strain, user proximity, angle, etc. However, as the converted power is dependent on the received waves, the environment can influence the rectennas’ output. In all RF sensing efforts to date, the sensor itself is sensitive to variations in the sensing channel such as blockage or distance variations. These variations require a referencing mechanism so that absolute measurements can be reliably taken and processed. Typically, this requires the use of an entirely new transceiver for each additional function which significantly adds to the cost and complexity of the system.

[0008] There is, therefore, a need to realise an antenna system that is able to simultaneously and reliably perform multiple functions without requiring the addition of complex, costly, and / or fragile components.

[0009] The present invention has been devised in light of the above considerations.

[0010] Summary of the Invention

[0011] In a general sense, the present invention provides a lightweight, low-cost, easy-to-manufacture antenna system capable of simultaneously carrying out multiple functions including powering devices using an incident signal and processing / analysing said signal without compromising the quality of the output of any of these functions. The antenna system described herein therefore provides a significant improvement over and above the multi-transceiver system. In a first aspect, there is provided an antenna system comprising: a receiving antenna section configured to receive a wireless radio frequency signal; a rectifier system connected to the receiving antenna section by a primary transmission line that is configured to convey the radio frequency signal received by the receiving antenna section, wherein the rectifier system is configured to convert the received radio frequency signal into a direct current power signal; a processing unit configured to be powered by the direct current power signal from the rectifier system; and a coupler configured to capacitively couple a portion of the radio frequency signal conveyed by the primary transmission line for processing by the processing unit without passing through the rectifier system.

[0012] In this way, the coupler facilitates the picking off of a signal that can be processed without the information carried in the signal being interfered with, scrambled, or even destroyed by, for example, a rectifier system or any other components that are configured to modulate a signal in such a way that the information carried by the signal would be altered.

[0013] Importantly, the antenna system disclosed herein is able to provide both a powering signal (via the rectifier system) and a picked-off signal useable for processing by the processing unit instead of requiring a wholly separate transceiver system for each functionality.

[0014] Herein the term “radio frequency signal” may mean any wirelessly transmittable electromagnetic signal. For example, the “radio frequency signal” may encompass microwave or mmWave signals, or any other signal suitable dependent on the context in which the antenna system is deployed.

[0015] In some embodiments, the antenna system may further comprise a secondary transmission line connected to the coupler to convey the coupled portion of the radio frequency signal. The secondary transmission line may bypass the rectifier system /

[0016] In some examples, the capacitive coupling between the primary transmission line and the secondary transmission line may be achieved across a physical separation of these transmission lines. In some examples, a dielectric may be provided in the space separating the transmission lines.

[0017] In some examples, the antenna system may be implemented as a waveguide system, wherein each of the primary and secondary transmission lines are defined by respective waveguides. The waveguide system may, for example, be a planar waveguide system. For example, the secondary transmission line may be capacitively coupled to the primary transmission line by providing the transmission lines as physically separated co-planar waveguides or microstrip lines. These separated waveguides may be separated by a layer or section of dielectric material.

[0018] In some embodiments, the antenna system may further comprise a receiver unit connected to the coupler and configured to extract data encoded in the coupled portion of the radio frequency signal. The processing unit may be configured to receive and process the extracted data.

[0019] In some embodiments, the receiver unit may be further configured to: determine a signal strength of the coupled portion of the radio frequency signal; and convey the determined signal strength to the processing unit separately from the extracted data. In this way, the antenna system may be able to reliably and simultaneously carry out three distinct functions: (i) powering the processing unit via the primary transmission line, (ii) receiving and processing information carried by the incident signal, and (iii) carrying out measurements of the antenna system’s environment based on the signal strength of the picked-off signal.

[0020] In some examples, the signal strength of the picked-off signal may be determined as a conventional received signal strength indicator (RSSI) value.

[0021] In some embodiments, the receiving antenna section may be impedance-matched with the rectifier system.

[0022] In this way, losses between the receiving antenna section and the rectifier system may be minimised.

[0023] For example, the receiving antenna section and rectifier system may be matched by tuning the receiving antenna section such that the impedance of the receiving antenna section is equal to the impedance of the rectifier system. In other examples, the complex conjugate of the impedance of the receiving antenna section may be equal to the impedance of the rectifier system.

[0024] In some embodiments, the antenna system may further comprise a power conditioning unit configured to adapt the powering signal.

[0025] For example, the power conditioning unit may be configured to modulate the powering signal. Modulating the powering signal may include gating and / or boosting the powering signal.

[0026] In this way, it may be possible to modulate the powering signal such that the eventual signal provided to power the processing unit is more suitable for providing power, e.g., because the powering signal provided is more continuous, higher-Zlower-current, or higher-Zlower-voltage.

[0027] For example, the power conditioning unit may be configured to modulate the voltage of the powering signal.

[0028] In some embodiments, the power conditioning unit may comprise a boost converter.

[0029] The boost converter may be configured to step-up the voltage of the powering signal, thereby steppingdown the current of the powering signal such that it is safe to pass through the processing unit.

[0030] In some examples, the power conditioning unit may be part of a wake-up radio receiver. In this way, the system may be able to wake-up and receive a packet when the incident power reaches a certain threshold.

[0031] In some embodiments, the power conditioning unit may comprise an energy storage unit.

[0032] The energy storage unit may be configured to smooth variations in the voltage of the powering signal caused by passing the incident signal through the rectifier system to define the powering signal. In this way, the processing unit may be able to draw a more consistent power level during use of the antenna system, thereby providing a more efficient and reliable output from the processing unit.

[0033] The energy storage unit may, for example, be a capacitive storage unit or a battery. In some embodiments, the receiving antenna section may comprise an array of antennas.

[0034] In other words, in some embodiments, the receiving antenna section may be defined by a single antenna, while in other embodiments the receiving antenna section may be defined by a plurality of antennas.

[0035] In some embodiments, the array of antennas may comprise a plurality of coupled antennas.

[0036] In some examples, some or all of the antennas may be mutually coupled.

[0037] By providing the antennas of the receiving antenna section as an array of mutually coupled antennas, it is possible to simultaneously tune all of the coupled antennas to the same operating frequency.

[0038] In some embodiments, the antenna system may further comprise a transmitter unit and a transmitter antenna. The transmitter unit may be configured to receive output from the processing unit, and to convey said output to the transmitter antenna for external communication.

[0039] In this way the results of any processing and / or analysis carried out by the processing unit may be communicated to an external device or system for further analysis / use / application.

[0040] In some embodiments, the transmitter antenna may be an antenna of the receiving antenna section.

[0041] In this way, the overall number of components required to manufacture the antenna system may be reduced because the transmitter antenna can be configured to operate with both receiving and transmitting functionality. This may result in a more lightweight antenna system that is easier to manufacture and operate.

[0042] In some examples, the transmitter antenna may be connected to both a receiver unit (e.g., via the transmission line), and the transmitter unit to facilitate the dual functionality of both receiving and transmitting signals.

[0043] In some embodiments, the transmitter unit may be a transceiver unit coupled to the transmitter antenna.

[0044] In this way the number of components and the complexity of the antenna system may be reduced, thereby facilitating a more lightweight antenna system that is easier to manufacture and operate.

[0045] In some embodiments, the transmitter antenna may be connected to the processing unit by a transceiver communication line.

[0046] Preferably, the transceiver communication line is distinct from the transmission line and facilitates two- way communication between the processing unit and an external device. By providing the transceiver communication line as distinct from the transmission line it is possible to establish a two-way communication channel that does not suffer from having signals conveyed therethrough being modulated, sampled, or otherwise altered.

[0047] In some embodiments, the transmission line is configured to pick-off no more than 1% of the incident signal from the primary transmission line.

[0048] It may be advantageous to minimise the amount of power picked-off from the primary transmission line by the transmission line (via the capacitive coupler) so that as much power as possible is retained in the primary transmission line for powering the processing unit. It is however necessary to ensure that enough of the incident signal is picked-off into the transmission line such that there is sufficient signal for the processing unit to be able to accurately and reliably process the coupled portion.

[0049] In some examples, the coupled portion may be 1 % or less of the incident signal, 0.5 % or less of the incident signal, 0.25% or less of the incident signal, 0.1% or less of the incident signal, 0.01 % or less of the incident signal, 103% or less of the incident signal, or 104% or less of the incident signal.

[0050] The ratio of the power of the coupled portion to the power of the incident signal may be expressed as a strength of the capacitive coupling in decibels. For example, if the capacitive coupling has a strength of OdB, this is indicative that all the power in the incident signal is picked-off into the transmission line. Meanwhile, a capacitive coupling having a strength of -20dB is indicative that 1% of the power in the incident signal is picked-off into the transmission line.

[0051] In some examples, the strength of the capacitive coupling may be -20dB or less, -30 dB or less, -40 dB or less, -50 dB or less, or -60 dB or less.

[0052] In some examples, the strength of the capacitive coupling may be -60 dB or more, -50 dB or more, -40 dB or more, -30 dB or more, or -20 dB or more.

[0053] In some examples, the strength of the capacitive coupling may be between any of the values listed above. For example, the strength of the capacitive coupling may be between -20 and -60 dB, -20 and -50 dB, -20 and -40 dB, -20 and -30 dB, -30 and -60 dB, -30 and -50 dB, -30 and -40 dB, -40 and -60 dB, -40 and -50 dB, or -50 and -60 dB.

[0054] In some examples, the strength of the capacitive coupling may be tuneable, for example by adjusting the effective width of the capacitive coupling between the transmission line and the primary transmission line. This may, for example, be achieved by adjusting the amount of physical separation between the transmission line and primary transmission line. In some examples, the strength of the capacitive coupling may be tuneable between any of the values set out above.

[0055] For example, the strength of the capacitive coupling may be tuneable between -20 and -60 dB, -20 and - 50 dB, -20 and -40 dB, -20 and -30 dB, -30 and -60 dB, -30 and -50 dB, -30 and -40 dB, -40 and -60 dB, - 40 and -50 dB, or -50 and -60 dB.

[0056] The inventors have found that, within the configurations for the antenna system described herein, strengths of the capacitive coupling within the ranges set out above are suitable for simultaneously providing power to the processing unit via the powering line, whilst simultaneously providing sufficient signal to the transmission line for the processing unit to be able to accurately and reliably process.

[0057] In some embodiments, an operating frequency of the antenna system may be tuneable.

[0058] In this way, the antenna system may be more versatile and deployable in a wide range of contexts and use applications, for example, owing to the capability to change frequencies or power levels incident at the antenna. In some embodiments, the receiving antenna section may be electrically DC-blocked from the rectifier system.

[0059] In other words, the receiving antenna section may be interfaced into the output of the rectenna via the rectifier system that is a DC-blocking interface.

[0060] A DC blocker may be particularly useful to reduce the risk of DC signals interfering with the radio frequency inputs received by antennas of the receiving antenna section.

[0061] The DC-blocking (or electrical isolation) of the receiving antenna section from the rectifier system may be a DC-isolation. In some examples, this blocking / isolation may be achieved by placing one or more capacitors between the receiving antenna section and the rectifier system, as part of a voltage-doubling rectifier. Alternatively, rectification may be achieved by placing one or more fully integrated charge-pumps between the receiving antenna section and the DC power conditioning unit.

[0062] In some embodiments, the antenna system may further comprise an analog-to-digital converter configured to receive an output indicative of the signal voltage at the receiving antenna.

[0063] An input to the analog-to-digital converter may be connected to an input of the rectifier system by a high impedance line that runs in parallel with the primary transmission line. In this way, the time variations and fluctuations in the DC output of the rectennas can be monitored for integrated RF sensing. Having a high impedance may reduce the amount of current drawn by the analog-to-digital converter. In this way, it may be possible to ensure that sufficient current is always drawn to power the processing unit.

[0064] In some embodiments, the antenna system may further comprise one or more additional sensors connected to the analog-to-digital converter. The analog-to-digital converter may be configured to convey signals from the one or more additional sensors to the processing unit.

[0065] The one or more additional sensors may be powered by their own power supplies, or they may derive power from the receiving antenna section.

[0066] In this way, the sensing capabilities of the antenna system may be improved (i.e., made more versatile).

[0067] In some examples, the processing unit may include a microcontroller. The microcontroller may be configured to control the one or more additional sensors and / or the analog-to-digital converter.

[0068] In some embodiments, the antenna system may be configured to monitor the occupancy of a room or provide data for localising individuals within a space based on one or more properties of the received radio frequency signal determined by the processing unit.

[0069] For example, the monitoring may be based on a DC voltage level of the rectenna and / or a measured RSSI value of the received signal, as determined by the processing unit.

[0070] In some examples, the antenna system may be implemented using a planar and / or conformable array. The array may, in some examples, be fitted to the fixtures of an indoor space. The antenna system may be powered using one or more (optionally distributed) radio frequency power transmitters that are configured to provide enough power to intermittently power one or more additional sensors such as smoke detectors, ambient temperature monitors, and / or light-level monitors. The propagation of a radio frequency signal transmitted by the radio frequency transmitter(s) may be affected by the presence of occupants in the indoor space. As such, the antenna system may be useable as a room occupancy sensor, or provide data for further functionality - including, but not limited to, the localisation of individuals and / or head-counting. Variations in received voltage levels form the antenna system can be recorded and classified using an appropriate analysis approach, for example classification may be implemented by an appropriately trained machine learning model.

[0071] In some embodiments, the antenna system may be mountable on a portable or wearable device.

[0072] In some embodiments, the antenna system may be integrated in a wirelessly connectable device.

[0073] In some examples, the antenna system may be useable to power a wearable device (or any other suitable device), for example a fitness tracker, healthcare sensor, or a pair of wireless headphones. The antenna may be configured to power the wearable device based on incident signals received from a nearby radio frequency power transmitter. The radio frequency power transmitter could be integrated and / or powered from, for example, a personal computer or phone. This powering device may be a device that belongs to the user of the wearable device. The radio frequency power transmitter could also be deployed in a vehicle, such as a motor vehicle, train, plane, or similar, where the user is stationary over a prolonged period of time.

[0074] By exploiting the antenna system’s ability to split the incident signal into different lines, two-way communication between the radio frequency power transmitter and the radio frequency-powered device (e.g., the wearable device) may be established without impacting on the wireless charging performance of the antenna system (as may be provided by the first transmission line).

[0075] In some examples, the power of the incident radio frequency signal may be dependent on the position of the antenna system relative to the source of the signal. In contexts where the antenna system is mounted on a wearable device, this dependency may facilitate radio frequency-based sensing of user activities including gestures, motion, breathing, and / or cardiac activity (e.g., heart rate).

[0076] In some examples, the antenna system may be powerable by a mobile energy harvesting source, for example a dynamo or generator mounted on a vehicle. For example, on a motorbike or bicycle (or any other suitable vehicle, e.g., a car, bus, tram, train, etc.), the radio frequency power may be supplied from a generator that depends on the travelling speed of the vehicle. In this way, events such as falls, sudden stops, sharp acceleration / deceleration and other variations in motion may be detected by capitalising on the antenna system’s ability to simultaneously receive power from an incident radio frequency signal, and monitor one or more properties of the signal, e.g., an RSSI value, and / or a continuous voltage level associated with the receiving antenna section (e.g., an antenna array making up the receiving antenna section).

[0077] In some examples, a transmitting antenna and / or transmitting sub-system of the antenna system may be based on readily available RFID readers / transmitters or alternatively on bespoke circuitry. In another aspect, there is provided a method of manufacturing the antenna system according to any preceding claim, the method comprising: providing a rectenna having a receiving antenna section, and a primary transmission line comprising a rectifier system; and capacitively coupling a secondary transmission line to the primary transmission line of the rectenna at a point between an antenna of the receiving antenna section and the rectifier system such that the transmission line is able to pick-off a portion of a radio frequency signal received by an antenna of the receiving antenna section.

[0078] In other words, the antenna system described herein may be manufactured by retrofitting a transmission line to a pre-existing rectenna system.

[0079] In some embodiments, the rectenna may further comprise a processing unit for processing the incident signal, said processing unit powered by a direct-current powering signal supplied by the receiving antenna section via the rectifier system. The method may further comprise connecting the transmission line to the processing unit such that the coupled portion is conveyable to the processing unit through the transmission lien without passing through the rectifier system.

[0080] In some examples, the processing unit may be connected to a pre-existing sensing antenna structure enabling the processing unit to process signals received from said sensing antenna structure. In such examples, the method may further comprise disconnecting the processing unit from said sensing antenna structure. In such examples, the RF sensing system may be composed of a combination of multiple antennas, where one or more antennas are useable as a reference. The reference antennas may allow the receiver to isolate unwanted channel variations and sense the environment based on changes in the sensing antenna’s gain.

[0081] In other examples, retrofitting the transmission line to the rectenna may enable to newly formed antenna system to provide additional functionality in the form of a sensing functionality that the rectenna was previously incapable of providing.

[0082] In some embodiments, the method may further comprise: connecting the primary transmission line of the rectenna to a processing unit configured to process the incident signal; and connecting the transmission line to the processing unit such that the coupled portion of the incident signal is conveyable to the processing unit through the transmission line without passing through the rectifier system.

[0083] In other words, the method may further comprise connecting a processing unit to the retrofitted rectenna, thereby defining the antenna system described herein.

[0084] In some examples, the antenna systems described herein (and, optionally, their power supply in the form of a radio frequency transmitter) may be retrofitted to existing DC power supplies including, but not limited to, power rails for trains.

[0085] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided. Summary of the Figures

[0086] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0087] Figure 1 shows an exemplary antenna system that is an embodiment of the invention.

[0088] Figure 2a shows an example of a receiving antenna section coupled to a rectifier system having a single antenna.

[0089] Figure 2b shows an example of a receiving antenna section coupled to a rectifier system having an array of antennas.

[0090] Figure 3 shows an example of a power conditioning unit of the antenna system.

[0091] Figure 4 shows an exemplary antenna system that is another embodiment of the invention.

[0092] Figure 5a shows an exemplary antenna system that is another embodiment of the invention.

[0093] Figure 5b shows a dual-transmitter sensing system configured to operate in conjunction with the antenna system described herein.

[0094] Figure 6 shows an exemplary antenna system that is another embodiment of the invention.

[0095] Figure 7 shows an exemplary antenna system that is another embodiment of the invention.

[0096] Figure 8a shows a cross section of the receiving antenna section of the antenna system described herein having a microstrip line in proximity with the receiving antenna section defining the secondary transmission line of the antenna system.

[0097] Figure 8b shows a plan view of the receiving antenna section shown in Figure 8a.

[0098] Figure 8c shows an alternative plan view of the transmission line positioned in proximity to the primary transmission line of the antenna system.

[0099] Figure 9 shows a plot of the input reflection coefficients and a forward transmission coefficient associated with an exemplary antenna system having an array of three input antennas.

[0100] Figure 10 shows a plot of the forward transmission in the primary direction for an exemplary antenna system having an array of three input antennas.

[0101] Figure 11 shows a plot of the forward transmission from the receiving antenna section to the capacitively coupled transmission line as a function of the clearance distance between the secondary transmission line and primary transmission line.

[0102] Figure 12a shows a plot of the RF to DC conversion efficiency and DC voltage output of the rectifier system for different capacitive coupling values.

[0103] Figure 12b shows a zoomed-in section of the plot of Figure 12a showing the RF-DC efficiency loss for different capacitive coupling values.

[0104] Figure 13 shows plots of a reflection coefficient of the rectifier system, with input matching at 868 MHz. Figure 14 shows a coupling between the receiver and the input from the antenna at 868 MHz.

[0105] Figure 15 shows coupling between the receiver and input as a function of frequency.

[0106] Detailed Description of the Invention

[0107] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0108] Figure 1 shows an exemplary antenna system 100. The antenna system comprises a primary transmission line 102 configured to convey an incident signal from a receiving antenna section 110 to a rectifier system 120. Exemplary configurations of the receiving antenna section 110 and rectifier system 120 will be described in more detail in relation to Figures 2a and 2b below.

[0109] The receiving antenna section 110 is configured to receive an incident radio frequency signal. This received incident signal is conveyed through the primary transmission line 102 towards the rectifier system 120. This rectifier system is configured to convert the incident radio frequency signal to a direct- current powering signal suitable for powering one or more other components of the antenna system 100.

[0110] Meanwhile, a capacitive coupler 130 disposed in close proximity to the primary transmission line 102 is arranged such that it picks-off (i.e. , couple out) a portion of the incident signal from the primary transmission line 102 at a position between the receiving antenna section 110 and the rectifier system 120. The coupled portion is conveyed through a transmission line 132. Importantly, the coupled portion conveyed through the transmission line 132 does not pass through the rectifier system or any other modulation component that risks the modulation, deterioration, or even elimination of any data carried by the incident signal. Instead, the coupled portion of the incident signal is conveyed through the transmission line to a receiver unit 134 that is configured to extract data encoded in the coupled portion of the incident signal. The receiver unit 134 is also configured to separately determine a signal strength of the coupled portion (e.g., in the form of a RSSI value, as described herein). Once the data has been extracted and / or the signal strength determined, the receiver unit 134 is configured to separately convey the extracted data and / or the determined signal strength to one or more other components of the antenna system 100, e.g., as separate or otherwise distinguishable signals.

[0111] Preferably, the coupled portion of the incident signal corresponds to less than 1 % of the power of the incident signal. In particular, the power ratio of the coupled portion to the incident signal may be in the range of -20 to -60 dB. This power ratio is tuneable by adjusting the amount of the physical separation between the primary transmission line 102 and the transmission line 132 (said separation itself defining the capacitive coupler 130). For example, adjusting the physical separation between the primary transmission line 102 and the transmission line 132 may be achieved by varying the spacing and width of PCB traces on which the transmission lines 102, 132 are implemented. A similar approach for adjusting the physical separation can be used on an integrated circuit, where the transmission lines 102, 132 and capacitive coupler 130are implemented on a semiconductor chip, such as a CMOS chip. It is noted that not all embodiments of the antenna system 100 disclosed herein require the provision of a receiver unit 134. For example, as an alternative, the transmission line 134 may convey the coupled portion from the capacitive coupler 130 directly to another component of the antenna system 100, such as a processing unit 150. However, in examples where the receiver unit 134 is provided, the receiver unit 134 may comprise a low-noise amplifier and / or voltage detector.

[0112] The antenna system 100 may further comprise a DC power conditioning unit 140 connected to receive an output from the rectifier 120 via transmission line 103. The DC power conditioning unit 140 is configured to adapt the DC power signal output from the rectifier system 120 to be suitable for further use.

[0113] Exemplary configurations of the DC power conditioning unit 140 will be described in more detail in relation to Figure 3.

[0114] The antenna system 100 further comprises a processing unit 150 configured to process the incident signal. The processing unit 150 is configured to receive a power signal output by the DC power conditioning unit 140 (or directly from rectifier 120 if the DC power conditioning unit 140 is omitted) on transmission line 104. The processing unit 150 is operable to receive and process the coupled portion of the incident signal conveyed via the transmission line 132. This coupled portion is received by processing unit 150 from the receiver unit 134, preferably in the form of an extracted data portion 136 and a determined signal strength portion 138 (e.g., in the form of a determined RSSI value).

[0115] The processing unit 150 may, for example, comprise a microcontroller configured to analyse the determined signal strength received from the receiver unit 134. The microcontroller may be further configured to determine one or more properties of the contextual environment measured by the receiving antenna section 112 based on the determined signal strength.

[0116] For example, as discussed above, the antenna system 100, and other examples of the antenna system disclosed herein, may be used for occupancy monitoring of indoor spaces, speed monitoring of vehicles, or motion / gesture / breathing / heart rate monitoring of a user (i.e., wearer) of a wearable device.

[0117] The processing unit 150 may further comprise a communications unit configured to receive and process the extracted data received from the receiver unit 134. The extracted data may, for example, include one or more instructions configured to cause the processing unit 150 to execute a particular process. For example, the instructions may include one or more of (i) tuning an operating frequency of the receiving antenna section 110, (ii) modulating a power consumption level of the antenna system 100, (iii) adjust the capacitive coupling of the transmission line 132 to the primary transmission line 102 through the capacitive coupler 130, and / or any other suitable instruction.

[0118] The communications unit may additionally or alternatively be configured to generate a communication signal for transmission to an external device / environment. This communication signal may, for example, contain information indicative of the one or more properties determined by the microcontroller. The communication signal may additionally or alternatively include status information indicative of the operational status of the antenna system 100. This status information may, for example, include information indicative of one or more of: (i) the power level of the antenna system 100, (ii) an operating frequency of the receiving antenna section 110, (iii) an amount of capacitive coupling, through the capacitive coupler 130, between the primary transmission line 102 and the transmission line 132, (iv) data received from one or more additional sensors 170 (see below) of the antenna system, and / or any other suitable information.

[0119] The antenna system 100 may, in some examples, further comprise an analog-to-digital converter 160 configured to receive an output indicative of the signal voltage at the receiving antenna. This output is obtained by providing a parallel high impedance line 162 at the input to the rectifier system 120. The analog-to-digital converter 160 operates to convert the AC signal on the high impedance line 162 into an input suitable for the processing unit 150. In this way the processing unit can monitor or otherwise utilise the information about the voltage of the receiving antenna section when processing the signals from the receiver 134.

[0120] The analog-to-digital converter 160 may be configured to receive analog output signals from one or more additional sensors 170, where the output signals reflect properties observed or otherwise measured by said sensor(s) 170. The analog-to-digital converter 160 may be configured to convert each analog output signal into a digital signal suitable for handling by the processing unit 150. In preferred examples, the analog-to-digital converter 160 is directly connected to the processing unit 150. In some examples, the analog-to-digital converter 160 and processing unit 150 may be implemented as parts of a common microcontroller integrated circuit.

[0121] A high impedance line 162 is used for this purpose because analog-to-digital converters do not need to draw large levels of current to be powered. It is desirable to minimise the amount of power that is coupled out of the primary transmission line 102 to ensure that the processing unit 150 receives as much power as possible from the original signal.

[0122] The antenna system 100 may further comprise a transmitter unit 180 connected to the processing unit 150. The transmitter unit 180 is configured to receive communication signals generated by the communications unit and modulate them to be suitable for transmission by a transmitting antenna 190. For example, the transmitter unit 180 may encode the communication signal into a RF carrier wave for transmission.

[0123] Figure 2a shows an example of a receiving antenna section 110 coupled to a rectifier system 120 having a single antenna 112. The combined system comprises a single antenna 112 connected in series to a diode 122. The diode 122 implements the function of the rectifier system 120 to convert the RF signal collected by the antenna 112 into a direct-current powering signal. At a point between the antenna 112 and the diode 122, the capacitive coupler 130 is arranged to pick-off a portion of the incident signal, as discussed above.

[0124] Figure 2b shows an alternative example of a receiving antenna section 110 coupled to a rectifier system 120 having an array of antennas 112a-c. The combined system comprises a plurality of antennas 112a-c, each antenna connected to a system of diodes 122a-f. The system of diodes 122a-f defines the rectifier system 120 of the antenna system 100, while the plurality of antennas 112a-c defines the receiving antenna section 110 of the antenna system. To ensure correct operation, the rectifier system 120 of the antenna system 100 is connected to earth 124.

[0125] Each antenna 112a-c of the receiving antenna section 110 is electrically isolated from the system of diodes 122a-f defining the rectifier system 230 by a plurality of isolators 114a-c. Each isolator may 114a-c may, for example, by a capacitor, or a fully integrated charge-pump. This DC isolation may be used to multiply the rectified DC voltage to achieve a higher sensitivity to voltage variations.

[0126] At a point between a first antenna 1 12a and a first diode 122a, the capacitive coupler 130 is arranged to pick-off a portion of the incident signal, as discussed above.

[0127] As the skilled person will appreciate, either of the systems illustrated in Figure 2a or 2b, or any other technically equivalent system for providing a receiving antenna section 110 and rectifier system 120 may be provided as components of the antenna system 100 of Figure 1.

[0128] Figure 3 shows an example of a power conditioning unit 140 of the antenna system. The power conditioning unit 140 comprises a DC boost converter 142 configured to perform maximum power point tracker (MPPT) boosting on the powering signal to step-up the voltage of the powering signal output from the rectifier system 120 (and correspondingly stepping-down the current of said powering signal) to be suitable for powering the processing unit 150. The DC boost converter 142 is arranged to receive a low- power output from the rectifier system 120.

[0129] The power conditioning unit 140 may preferably (but not necessarily) further comprise a storage unit 144 that is arranged to receive a high-power output from the rectifier system 120. The storage unit may, for example, by a capacitor or supercapacitor defining a capacitive storage unit 144. Alternatively, the storage unit 144 may be a battery. The storage unit 144, due to its capacitance in the case of a capacitive storage unit, is suitable for smoothing out the power distribution to the processing unit 150, thereby providing a more consistent power source for the processing unit 150. A battery may also be suitable for providing a smoothed power distribution.

[0130] The power conditioning unit 140 further comprises a power gating switch 146 configured to facilitate operation of the system at low input voltages, e.g., in a scenario where the input signal has a voltage less than the threshold voltage of the DC boost converter 142. The power gating switch is controlled based on the outputs of first and second voltage monitors 148a, 148b. The first voltage monitor 148a delivers an output based on a voltage associated with the storage unit 144, while the second voltage monitor 148b delivers an output based on a voltage associated with an output of the power gating switch 146. In this way, the power gating switch 148 is operable as a hysteresis switch between two voltage thresholds. When the voltage across the power gating switch 146 is between these two thresholds, power is fed through the hysteresis switch to the processing unit 150.

[0131] Figure 4 shows an exemplary antenna system 100. The antenna system 100 shown in Figure 4 is an exemplary embodiment of the antenna system depicted in Figure 1. The receiving antenna section 110 and the rectifier system 120 is defined by the configuration shown in Figure 2b. The antenna system 100 further comprises a DC power conditioning unit 140, and analog-to-digital converter 160, with or without one or more additional sensors 170 as described above in relation to Figure 1. The analog-to-digital converter 160 samples the voltage output from the rectifier through a high-impedance interface line 162 connecting the rectifier system 120 to the analog-to-digital converter. The ADC shares the same power supply with the system 103, charged using the full antenna array 100.

[0132] Figure 5a shows an alternative exemplary antenna system 100. The antenna system 100 shown in Figure 5a is an exemplary embodiment of the antenna system depicted in Figure 1. The receiving antenna section 110 and the rectifier system 120 are defined by the configuration shown in Figure 2a. The antenna system 100 further comprises a DC power conditioning unit 140, as shown in Figure 3. The processing unit 150 is further connected to the antenna 112 of the receiving antenna section 110 via the transmitter unit 180. In other words, the antenna 112 of the receiving antenna section 110 is configured to operate as the transmitting antenna 190 shown in Figure 1 . In this context, the antenna 112 may be configured to operate in a receiver and a transmitter in orthogonal polarisation to avoid the reception and transmission functionalities from interfering with each other.

[0133] Figure 5b shows a dual-transmitter sensing system 200 configured to operate in conjunction with the antenna system 100, such as that shown in Figure 5a. The dual-transmitter sensing system 200 comprises a transmission node 202 that transmits information from a sensing transmission antenna 204 (i.e. , an antenna configured to transmit a signal whose strength has been modulated as a result of the environment that sensing system 200 is deployed in) and a reference antenna 206 that transmits a signal that is insensitive to the measurements carried out by one or more sensors of the sensing system 200. The variable capacitance and resistor of the sensing transmission antenna 204 depicted in Figure 5b denote the antenna’s own gain changes as a result of external parameters such as strain, relative permittivity, or temperature. These changes modulate the antenna’s gain thus creating an amplitude modulation based on the environment of operation.

[0134] The antenna system 100 described herein, by virtue of its separated primary transmission line 102 and transmission line 132 is able to use a majority of the signals received from the transmission antennas 204, 206 to power the processing unit 150. Meanwhile, the coupled portions of the signals transmitted by the two transmission antennas 204, 206 can be compared by the receiver unit 134 and processing unit 150 to extract so-called sensing information (based e.g. on the signal strength in the form of RSSI values) to determine information about the environment in which the dual-antenna transmission system 200 is deployed in.

[0135] Figure 6 shows another exemplary antenna system 100. The antenna system 100 shown in Figure 6 is an exemplary embodiment of the antenna system depicted in Figure 1. The receiving antenna section 110 and the rectifier system 120 is defined by the configuration shown in Figure 2a. The antenna system 100 further comprises a DC power conditioning unit 140, as shown in Figure 3. The processing unit is further connected to a transmitting antenna 190 via a transceiver unit 185 configured to facilitate two-way communication between the transmitting antenna 190 and the processing unit 150. The antenna 112 of the receiving antenna section 1 10 and the transmitting antenna 190 may be a pair of coupled antennas. Figure 7 shows another exemplary antenna system 100. The antenna system 100 shown in Figure 7 is an exemplary embodiment of the antenna system depicted in Figure 1. The receiving antenna section 110 and the rectifier system 120 is defined by the configuration shown in Figure 2b. The antenna system 100 further comprises a DC power conditioning unit 140, as shown in Figure 3. The antenna system 100 further comprises a DC power conditioning unit 140, and analog-to-digital converter 160 and one or more additional sensors 170 as described above in relation to Figure 1 . The analog-to-digital converter 160 is powered by a high-impedance interface line 162 connecting the rectifier system 120 to the analog-to- digital converter 160 that operates as a secondary power line.

[0136] Figure 8a shows a cross section view of the receiving antenna section 110 of the antenna system 100 described herein. The receiving antenna section 110 comprises a plurality of dipole-radiating antennas 112. Each antenna 112 comprises an inductive slot 1 16 for tuning the operating frequency of the antenna 112. The operating frequency of the antenna may be understood as being the frequency at which the dipole-radiating antenna 112 resonates. The operating frequency of the antenna 112 may be tuned by varying the dimensions of the inductive slot 116. The length of each dipole-radiating antenna may be, for example, 114 mm. With such an antenna, the operating frequency of the antennas 112 will be of the order of 100 MHz. Each antenna 112 is connected to a port of the rectifier system 120.

[0137] Additionally, a microstrip line 300 is provided in physical proximity to the antennas 112. The microstrip line (as will be discussed below in relation to Figure 8b) includes the transmission line 132. Preferably the microstrip line 300 is held away from the antennas 112 by a dielectric substrate 400. The separation between the transmission line 132 carried by the microstrip line 300 and the nearest of the antennas 112 of the receiving antenna section 110 may, for example, be approximately 2.5 mm.

[0138] Figure 8b shows a plane view of the receiving antenna section 110 depicted in Figure 8a, with the microstrip line 300 bearing the transmission line 132 shown extending away from the receiving antenna section 110.

[0139] Figure 8c shows an alternative plan view of the transmission line 132 positioned in proximity to the primary transmission line 102. As can be seen from Figure 8c, the transmission line 132 (carried by the microstrip line 300) is separated from the primary transmission line 102 by a dielectric substrate 400. This physical arrangement shown in Figure 8c with orthogonally extending lines is, in effect a configuration with a microstrip coupled to a co-planar waveguide. The dielectric substrate 400 may be formed from any suitable high-resistivity material such as, for example, a polyimide or polyurethane.

[0140] Figure 9 shows a plot of the input reflection coefficients and a forward transmission coefficient associated with an exemplary antenna system 100 having a receiving array section 110 comprising an array of three antennas 112. The antenna system 100 for which data has been plotted in Figure 9 has an operating frequency of 868 MHz. As can be seen from Figure 9, the reflection coefficient of each antenna is between -10 and -20 dB indicating that between 90 and 99% of the incident radiation is successfully coupled into the rectifier system 120. Meanwhile, the forward transmission coefficient from one of the antennas to the coupled line is shown to be less than -25 dB, indicating that the forward transmission does not affect the antenna’s 112 matching or reduce the power received by the rectifier. Figure 10 shows a plot of the forward transmission in the primary direction from the receiving antenna section 110 to the rectifier system 120 for an exemplary antenna system 100 having a receiving antenna section 110 comprising an array of three antennas 112. Figure 10 clearly shows that there is less than a 1dB loss in the transmission from the receiving antenna section 110 to the rectifier system 120 all the way up to an operating frequency of 2.6 GHz. As such, it can be clearly seen that the antenna system 100 described herein is operable across a wide range of frequencies.

[0141] Figure 11 shows a plot of the forward transmission from the receiving antenna section 110 to the capacitively coupled transmission line 132 as a function of the clearance distance between the secondary transmission line 132 and the primary transmission line 102. It can be clearly seen that the strength of the capacitive coupler 130 can be tuned from -20 dB to -75 dB by varying the operating frequency of the antenna system 100 from 0.3 to 3 GHz, and the physical separation between the secondary transmission line 132 and the primary transmission line 102 from 0 to 2.5 mm.

[0142] Figure 12a shows a plot of the RF to DC conversion efficiency and DC voltage output of the rectifier system 120 for different capacitive coupling values, indicating that the coupling of power into the receiver does not affect the DC output of the system.

[0143] Figure 12b shows a zoomed-in section of the plot of Figure 12a that highlights that the variation in the RF- to-DC efficiency for low coupling values (under -30 dB) is less than 0.5 % indicating that the performance of the antenna system 100 is robust across a broad a range of coupling levels.

[0144] Figure 13 shows a plot of the reflection coefficient of the rectifier system 120 of the antenna system 100, with input matching at 868 MHz, for a range of capacitive coupling strengths. As can be seen from Figure

[0145] 13, the capacitive coupling provided by the capacitive coupler 130 has no effect on the input matching of the rectifier system 120. This demonstrates that it is possible to retrofit pre-existing rectenna systems with a loosely (capacitively) coupled transmission line 132 to manufacture the antenna system 100 described herein.

[0146] Figure 14 shows a coupling between the receiver and the input from the receiving antenna section 110, at 868 MHz, for a range of capacitive coupling strengths, from 0.002 to 0.1 pF. As can be seen from Figure

[0147] 14, the coupling between the receiver and the input for the receiving antenna section 110 is independent of the power of the signal received by the antenna(s) 112 of the receiving antenna section 110.

[0148] Figure 15 shows a coupling between the receiver and input as a function of frequency, for a range of capacitive coupling strengths. As can be seen from Figure 15, sufficient power can be coupled from the primary transmission line 102 even out-of-band (i.e. , at frequencies remote from 868 MHz) to allow the receiver 134 to receive the data 136 and perform any sensing functionalities 138, while the power is being delivered to the rest of the system 104. .

[0149] ***

[0150] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0151] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0152] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0153] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0154] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0155] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

[0156] Reference Numerals

[0157] 100 Antenna system

[0158] 102 Primary transmission line

[0159] 103 Transmission line

[0160] 104 Transmission line

[0161] 110 Receiving antenna section

[0162] 112 Antenna

[0163] 114 DC-blocker

[0164] 116 Inductive slot

[0165] 120 Rectifier

[0166] 122 Diode

[0167] 124 Ground

[0168] 130 Capacitive coupler

[0169] 132 Transmission line Receiver unit

[0170] Extracted data portion

[0171] Determined signal strength portion DC power conditioning unit DC boost converter

[0172] Storage

[0173] Power gating switch a First voltage monitor b Second voltage monitor

[0174] Processing unit

[0175] Analog-to-digital converter High-impedance interface line Sensors

[0176] Transmitter unit

[0177] Transceiver unit

[0178] Antenna

[0179] Dual-antenna transmission system Transmission node

[0180] Sensing transmission antenna

[0181] Reference antenna

[0182] Microstrip line

[0183] Dielectric substrate

Claims

Claims:1 . An antenna system comprising: a receiving antenna section configured to receive a wireless radio frequency signal; a rectifier system connected to the receiving antenna section by a primary transmission line that is configured to convey the radio frequency signal received by the receiving antenna section, wherein the rectifier system is configured to convert the received radio frequency signal into a direct current power signal; a processing unit configured to be powered by the direct current power signal from the rectifier system; and a coupler configured to capacitively couple a portion of the radio frequency signal conveyed by the primary transmission line for processing by the processing unit without passing through the rectifier system.

2. The antenna system of claim 1 further comprises a secondary transmission line connected to the coupler to convey the coupled portion of the radio frequency signal, wherein the secondary transmission line bypasses the rectifier system.

3. The antenna system according to claim 1 or 2, further comprising a receiver unit connected to the coupler and configured to extract data encoded in the coupled portion of the radio frequency signal, wherein the processing unit is configured to receive and process the extracted data.

4. The antenna system according to claim 3, wherein the receiver unit is further configured to: determine a signal strength of the coupled portion of the radio frequency signal; and convey the determined signal strength to the processing unit separately from the extracted data.

5. The antenna system according to any preceding claim, wherein the receiving antenna section is impedance-matched with the rectifier system.

6. The antenna system according to any preceding claim, wherein the rectifier system comprises a power conditioning unit configured to adapt the direct current power signal for the processing unit.

7. The antenna system according to claim 6, wherein the power conditioning unit comprises a boost converter.

8. The antenna system according to claim 6 or 7, wherein the power conditioning unit comprises an energy storage unit.

9. The antenna system according to any preceding claim, wherein receiving antenna section comprises an array of antennas.

10. The antenna system according to claim 9, wherein the array of antennas comprises a plurality of coupled antennas.11 . The antenna system according to any preceding claim, further comprising a transmitter unit and a transmitter antenna, wherein the transmitter unit is configured to receive an output from the processing unit, and to convey said output to the transmitter antenna for external communication.

12. The antenna system according to claim 10, wherein the transmitter antenna is an antenna of the receiving antenna section.

13. The antenna system according to claim 1 1 or 12, wherein the transmitter unit is a transceiver unit coupled to the transmitter antenna.

14. The antenna system according to claim 13, wherein the transmitter antenna is connected to the processing unit by a transceiver communication line.

15. The antenna system according to any preceding claim, wherein the coupler is configured to couple no more than 1 % of the radio frequency signal from the primary transmission line.

16. The antenna system according to any preceding claim, wherein an operating frequency of the antenna system is tuneable.

17. The antenna system according to any preceding claim, wherein the receiving antenna section is DC-blocked from the rectifier system.

18. The antenna system according to any preceding claim, further comprising an analog-to- digital converter configured to receive an output indicative of the signal voltage at the receiving antenna.

19. The antenna system according to claim 18, wherein an input to the analog-to-digital converter is connected to an input of the rectifier system by a high impedance line that runs in parallel with the primary transmission line.

20. The antenna system according to any preceding claim, wherein the antenna system is configured to monitor the occupancy of a room or provide data for localising individuals within a space based on one or more properties of the received radio frequency signal determined by the processing unit.21 . The antenna system according to any preceding claim, wherein the antenna system is mountable on a portable or wearable device.

22. The antenna system according to any preceding claim, wherein the antenna system is integrated in a wirelessly connectable device.

23. A method of manufacturing the antenna system according to any preceding claim, the method comprising: providing a rectenna having a receiving antenna section, and a primary transmission line comprising a rectifier system; and capacitively coupling a secondary transmission line to the primary transmission line of the rectenna at a point between an antenna of the receiving antenna section and the rectifier system such that the transmission line is able to pick-off a portion of a radio frequency signal received by an antenna of the receiving antenna section.

24. The method according to claim 23, wherein the rectenna further comprises a processing unit for processing the radio frequency signal, said processing unit powered by a direct-current powering signal supplied by the rectifier system, and wherein the method comprises connecting the secondary transmission line to the processing unit such that the coupled portion of the radio frequency signal is conveyable to the processing unit through the secondary transmission line without passing through the rectifier system.

25. The method according to claim 23, further comprising: connecting the primary transmission line of the rectenna to a processing unit configured to process the radio frequency signal; and connecting the secondary transmission line to the processing unit such that the coupled portion of the radio frequency signal is conveyable to the processing unit through the transmission line without passing through the rectifier system.

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