Device for wireless communication using back-to-back antennas

Abstract

Device (20) for wireless communication, comprising a first antenna (12), a second antenna (22), and a hybrid coupler (11) connecting the first antenna (12) and the second antenna (22) to opposite transmission paths (TX), to potentially double the TX coverage of the space, wherein the first antenna (12) is connected to a first port (2) of the hybrid coupler (11), wherein the second antenna (22) is connected to a second port (3) of the hybrid coupler (11), and wherein the first antenna (12) and the second antenna (22) are mutually isolated and arranged in a back- to-back configuration.

Description

[0001]DEVICE FOR WIRELESS COMMUNICATION USING BACK-TO-BACK ANTENNAS FIELD OF THE INVENTION The present invention relates to a device and a method for wireless communication. BACKGROUND In wireless communications, simultaneous transmission and reception (STR) of signals ishighly desirable. Techniques such as frequency division duplex (FDD) or full-duplex (FD) havebeen developed or are currently in development to address this demand. For example, IEEEstandard 802.11be, also designated “Wi-Fi 7”, provides implementation for the support of FDD.However, there are many hurdles to overcome in the quest for achieving real, on-chip FD. Oneof these hurdles is to obtain a better degree of self-interference cancellation (SIC), in otherwords reducing the leakage of the transmitted signal onto the receive chain with very highpower. To address this issue, several solutions have been proposed. One approach is to utilize twoantennas, one of which is exclusively used for transmission (TX), and one of which is solelyused for reception (RX). This results in an inherent isolation between the transmission and thereception chains, and no reflection occurs. However, in order to achieve maximum coverage, this approach requires a large number of antennas which results in transceivers that are large and expensive.Another approach is to employ a single antenna for both reception and transmission inconjunction with an electrically balanced duplexer. For example, US 2010 / 304701 A1,proposes to use a transmission leakage signal apparatus comprising a reflection coefficient adjustment unit that outputs a signal to the reception path with the same amplitude and opposite phase than that of the signal or signals leaked from the transmission path. However, this solution requires a split of the transmission power between the antenna and the adjustment unit, as well as a split of the reception signal between the power amplifier (PA) and the low noise amplifier(LNA). Thus, the use of the adjustment unit leads to power losses on the order of 3dB for bothTX and RX.In view of this, it is an object of the present disclosure to provide an improved device forwireless communication. SUMMARY OF THE INVENTIONIn a first aspect of the present disclosure, this object is achieved with a device according toclaim 1. Implementations are set forth in the dependent claims.The device according to the first aspect comprises a first antenna, a second antenna, and a hybridcoupler connecting the first antenna and the second antenna to mutually independenttransmission paths, a first transmission path for the first antenna and a second transmission path for the second antenna. The first antenna is connected to a first port of the hybrid coupler, the second antenna is connected to a second port of the hybrid coupler, and the first antenna and the second antenna are arranged in a back-to-back configuration. In particular, the device may be a radio frequency front-end, RFFE. Herein, the term “back-to-back configuration” generally means that the first and the second antenna are oriented towards opposite sides, i.e., opposite hemispheres. Further, the antennasare arranged in close spatial proximity. For example, the first and the second antenna may bedirectional antennas, such as patch antennas arranged in such a way that they face oppositehemispheres, for example, the first and the second antenna may be provided on oppositesurfaces of the same substrate. However, it is also possible that each antenna is provided on aseparate substrate, but facing opposite directions. Furthermore, the first and the second antennaare preferably mutually isolated, in particular electrically isolated. Such an isolation can preventa mutual cancellation of the reception signals of the antennas inside the hybrid coupler.The term “hybrid coupler” is to be understood in its usual technical meaning, i.e., as a directional coupler designed to split power equally between two ports.By using the back-to-back configuration, it is possible to transmit signals with the first andsecond antennas in both hemispheres. In other words, a high spatial coverage is possible.Further, in the back-to-back configuration, the reflection signal from the first antenna can be cancelled by a corresponding reflection signal from the second antenna, and vice versa, without having to use additional electronic adjustment circuits.In other words, instead of shaping half of the TX signal in a dedicated circuit, as it is done inthe prior art, the invention shapes half of the TX signal in an identical antenna that also transmitsthe signal in a different direction, thus achieving a high degree of SIC and increasing the spatialcoverage from 180° to 360°. Implementations of the first aspect are described hereinafter.The hybrid coupler may be configured to supply the first antenna with power from the firsttransmission path and the second antenna with power from the second transmission path such that a reflection signal from the first antenna is at least partially cancelled by a reflection signalfrom the second antenna, and vice versa. In particular, the hybrid coupler may be configured toprovide the power such that the signals in the first and second antennas have a phase difference.In particular, the hybrid coupler may be a 0 / 180° hybrid coupler. In other words, the hybridcoupler may be configured to add the first antenna and the second antenna with a phase difference of 180°. In this case, a high degree of cancellation of a reflection signal from the first antenna by a reflection signal of the second antenna, and vice versa, may be achieved, inparticular without additional electronics. In particular, while the first antenna and the secondantenna will transmit with the same phase, a reflection signal from the first antenna will becancelled by a reflection signal from the second antenna inside the hybrid coupler at the receiveport.The first antenna and the second antenna may be of an identical type. For example, the firstantenna and the second antenna may be directional antennas, such as patch antennas. The first and second antennas may have the same internal structure. By utilizing identical types of antennas, cancellation of a reflection signal from the first antenna by a reflection signal of the second antenna, and vice versa, may be further improved.The hybrid coupler may further connect the first antenna and the second antenna to a receptionpath. Thus, both antennas may be used for transmission. On the other hand, simultaneousreception may impair reception as the receiver cannot differentiate between the two RX signals.So this may be utilized only in special cases whereas the common practice is to receive onlyfrom one direction and at the same time transmit to opposite directions. As such, the device may be used as a transceiver capable of STR with high spatial coverage and low self- interference.The device according may further comprise a first antenna array, and a second antenna array,wherein the first antenna array comprises the first antenna, wherein the second antenna arraycomprises the second antenna, and wherein the first antenna array and the second antenna arrayare arranged in a back-to-back configuration. By utilizing back-to-back antenna arrays,efficiency of the device may be further improved. The device may further comprise a first antenna tuner arranged between the first port and thefirst antenna, and a second antenna tuner arranged between the second port and the secondantenna. The use of the first and second antenna tuners may improve impedance matchingbetween the respective port and the antenna, leading to lower signal losses. In particular, theuse of antenna tuners may remove differences between the reflected signals from the first antenna and the second antenna, which may arise due to differences between the properties of the first antenna and the properties of the second antenna and / or differences between the signal path from the first port to the first antenna and the signal path from the second port to the second antenna. Further, antenna tuners may be used to offset internal leakage in the hybrid coupler.In particular, the first antenna tuner and / or the second antenna tuner comprise a Chebyshev-type antenna tuner. The Chebyshev-type antenna tuner may comprise an nth order Chebyshevbandpass filter, where n is between 1 and infinity, preferably between 2 to achieve 2 degrees oftuning freedom and 8, to keep power losses as low as possible and circuit size compact. TheChebyshev-type antenna tuner may be an antenna tuner such as disclosed in D. Regev, I. Melamed, N. Ginzberg and E. Cohen, "A Full Duplex RF Front End Employing an Electrical Balanced Duplexer and a Chebyshev Load-Balancing Filter," 2023 IEEE / MTT-S InternationalMicrowave Symposium - IMS 2023, San Diego, CA, USA, 2023, pp. 378-381, doi:10.1109 / IMS37964.2023.10188090. Such an antenna tuner may further improve impedance matching between the respective port and the antenna. According to a second aspect, the present disclosure provides a method for wireless communication, in particular using a device comprising one or more of the above-defined features. The method comprises: ^supplying a transmission signal, via a hybrid coupler, to a first antenna and a secondantenna; ^wherein the first antenna is connected to a first port of the hybrid coupler,^ wherein the second antenna is connected to a second port of the hybrid coupler, and^ wherein the first antenna and the second antenna are arranged in a back-to-backconfiguration; and ^transmitting the transmission signal via the first antenna and / or the second antenna.In an implementation of the second aspect, the method may further comprise ^adapting, via a first antenna tuner arranged between the first port and the first antenna,an impedance of the first port to match an impedance of the first antenna; and ^adapting, via a second antenna tuner arranged between the second port and the secondantenna, an impedance of the second port to match an impedance of the second antenna.The method may, in another implementation, further comprise receiving a signal via the firstantenna or the second antenna. Further implementations of the second aspect correspond to implementations described with respect to the first aspect.The advantages mentioned for the device described above for the first aspect and theimplementations thereof apply analogously to the corresponding features of the methoddescribed with respect to the second aspect and its implementations.According to a third aspect, the present disclosure provides a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the second aspect or one of the implementations thereof. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present disclosure will now be described in combination with the enclosed figures.Figure 1 schematically shows a device for reducing self-interference according tothe prior art;Figures 2 and 3 schematically show embodiments of a device for wireless transmission;andFigure 4 schematically shows two antennas in a back-to-back configuration.DETAILED DESCRIPTION OF THE INVENTIONFigure 1 schematically shows a device 10 for reducing self-interference according to the priorart. The device 10 comprises a four-port duplexer 11. The four-port duplexer 11 comprises afirst port 1, a second port 2, a third port 3, and a fourth port 4. The first port 1 is connected to a transmission path TX of a device for wireless communication. The fourth port 4 is connected to a reception path RX of a device for wireless communication. The four-port duplexer 11 may be, for example, a 0 / 180° hybrid coupler.The device 10 further comprises an antenna 12, which is used for transmission and reception.The antenna 12 is connected to the second port 2 of the four-port duplexer 11. The antenna 12has a reflection coefficient Γ^. The device 10 further comprises a load balancing module 13,which is connected to the third port 3 of the four-port duplexer 11. The load balancing module13 may comprise a circuit as, for example, known from US 2010 / 304701 A1. The loadbalancing module 13 has a reflection coefficient Γ^.The device 10 further comprises a power amplifier (PA) 14 arranged in the transmission pathTX and a low noise amplifier (LNA) 15 arranged in the reception path RX.In operation, a transmission signal enters the four-port duplexer 11 via the transmission pathTX and the power amplifier 14 with power PTX at port 1. Due to the properties of the four-portduplexer 11, the signal is distributed to ports 2 and 3 with a power loss of 3 dB. The signals are,thus, distributed to the antenna 12 and the load balancing module 13 with reduced power PTX’.At the antenna 12, reflection of the transmission signal occurs with reflection coefficient Γ^.The reflected signal is transferred back to the four-port duplexer 11 through port 2.The load-balancing module 13 generates, from the transmission signal with reduced power PTX’,a SIC signal with reflection coefficient reflection coefficient Γ^. This signal is fed back into thefour-port duplexer 11 through port 3 with power PSIC.The four-port duplexer 11 distributes the signals received through ports 2 and 3 from antenna12 and load-balancing module 13, respectively, to ports 1 and 4. The signals, again, be reducedby 3 dB. In particular, the SIC signal will have a reduced power PSIC’. As can be seen from Figure 1, these signals will also be transmitted to the RX path and the LNA 15. In order to prevent unwanted noise from the reflected transmission signal, it is necessary that the SIC signal that arrives in the RX path cancels the reflected signal. The cancellation condition is, thus, generally that the reflection coefficient Γ^is the inverse of the reflection coefficient Γ^, or that their absolutes are equal: Γ^ = − Γ^|Γ^| = |Γ^|In more detail, the total power leakage S41,D from the TX path to the RX path between the ports4 and 1 of the four-port duplexer may be approximated by the following formula:^^^,^ ≈ ^^^ + Γ^^^^^^^ + Γ^^^^^^^Herein, S represents the usual S-parameters, which denote the transfer function of the root square of the power transfer function.In this formula, S41 is direct leakage between ports 1 and 4 in the four-port duplexer. The termΓ^^^^^^^describes the reflected transmission signal from antenna 12. The term has acomponent S21 corresponding to the transmission signal as passed from port 1 to port 2, and acomponent passed from port 2 to port 4, i.e. to the RX path, modified by reflection coefficientΓ^. Analogously, the term Γ^^^^^^^describes the SIC signal generated by the load-balancing module 13. This term has a component S31 corresponding to the transmission signal as passedfrom port 1 to port 3, and a component passed from port 3 to port 4, i.e. to the RX path, in thereflection, modified by reflection coefficient Γ^.Generally, the direct leakage S41 will be small compared to the reflected components: ^^^ ≪ Γ^^^^^^^^^^ ≪ Γ^^^^^^^Thus, in order to achieve a small total power leakage S41,Dfrom the TX path to the RX path,i.e., ^^^,^ ≈ 0, the conditionΓ^^^^^^^ = −Γ^^^^^^^ should be fulfilled. In the prior art as illustrated in Figure 1, this requires careful tuning of the load-balancingmodule 13 to match the reflection signal coming from antenna 12.It is to be noted that the above only addresses the situation when a signal is sent. If a signal is received at the same time, an additional signal will be passed from the antenna 12 to thereception path RX with power PRX, reduced by 3 dB due to the four-port duplexer 11. However,since the circuit is linear, this does not change the above-discussed cancellation condition.Figure 2 illustrates a device 20 for wireless communication according to the present disclosure.In particular, the device 20 may be part of a RFFE.Like the device 10 illustrated in Figure 1, the device 20 comprises a four-port duplexer 11 withfour ports 1, 2, 3, and 4, a PA 14, and a LNA 15. The first port 1 is connected to a transmission path TX of a device for wireless communication, and the fourth port 4 is connected to a reception path RX of a device for wireless communication. In the illustrated embodiment, thefour-port duplexer 11 is a 0 / 180° hybrid coupler 11. As in device 10, device 20 also comprisesa first antenna 12, which the second port 2 of the hybrid coupler 11 connects to a firsttransmission path TX1. However, unlike the device 10 shown in Figure 1, the device 20 illustrated in Figure 2 comprisesa second antenna 22, which is connected by the third port 3 of the hybrid coupler 11 to a secondtransmission path TX2. The first antenna 12 and the second antenna 22 are of the same typeand are arranged in a back-to-back configuration, which is indicated by the opposite orientation of the symbols representing the antennas 12 and 22 in Figure 2. The first antenna 12 has a reflection coefficient Γ^^, and the second antenna 22 has a reflection coefficient Γ^^. Since the antennas 12 and 22 are of the same type, their properties, in particular their reflection coefficients, should be inherently identical: Γ^^ = Γ^^As discussed above, total power leakage S41,Dfrom the TX path to the RX path between the ports 4 and 1 of the four-port duplexer may approximated by the following formula: ^^^,^ ≈ ^^^ + Γ^^^^^^^^ + Γ^^^^^^^^ Again, assuming the direct leakage S41 to be negligible, the second and third terms inherently have the same magnitude due to the identical nature of antennas 12 and 22. Further, since the hybrid coupler 11 is a 0 / 180° hybrid coupler, the signal provided to antenna 12 has a 180° phase difference with the, otherwise identical, signal provided to antenna 22. As such, the cancellation condition Γ^^^^^^^^ = − Γ^^^^^^^^If the antennas are identical the condition is fulfilled due to the properties of the hybrid coupler 11. Further, since the antennas 12 and 22 are arranged back-to-back, the transmission signal is transmitted via antenna 12 into a first hemisphere and it is transmitted to the opposite hemisphere via antenna 22. Thus, device 20 doubles spatial coverage of the transmission compared to the prior art shown in Figure 1, while inherently reducing self-interference. It is to be noted that Figure 2 illustrates an embodiment with one first antenna 12 and one second antenna 22. However, it is possible that the first antenna 12 is part of a first antenna array which is connected to the second port 2 of the hybrid coupler 11, and that the second antenna 22 is part of a second antenna array which is connected to the third port 3 of the hybrid coupler 11. In this embodiment, the first antenna array and the second antenna array are also arranged in a back-to-back configuration.Figure 3 shows a further embodiment of the device 20 for wireless communication accordingto the present invention. Compared the embodiment shown in Figure 2, the device 20 asillustrated in Figure 3 further comprises an antenna tuner 16 arranged between the second port 2 of the four-port duplexer 11 and the first antenna 12, and an antenna tuner 16 arranged between the third port 3 of the four-port duplexer 11 and the second antenna 22. The antenna tuners 16 may be Chebyshev-type antenna tuners, in particular, the antenna tuners 16 may eachcomprise a nth order Chebyshev bandpass filter, where n is between 1 and infinity, in particularin between 2 and 8The antenna tuners 16 can be used to improve electrical balance. In particular, it is possible thatthe properties of antennas 12 and 22 are not fully identical, even if they are of the same type. Also, their reflection maybe impacted by different environments to which they are directed.Thus, small differences may exist in the reflected signals, and no full cancellation of thereflected signals may be achieved without the antenna tuners 16. For example, the reflectioncoefficient Γ^^ may be slightly different from the reflection coefficient Γ^^. The antenna tuners16 may be used to cancel these small differences by fine-tuning the impedances between port 2 and antenna 12, and port 3 and antenna 22, respectively. Further, the antenna tuners 16 may be used to offset direct leakage between ports 1 and 2 of thefour-port duplexer 11. As discussed above, it is possible that the first antenna 12 is part of afirst antenna array, and the second antenna 22 is part of a second antenna array.Figure 4 schematically shows a part of an embodiment of a device 20 for wirelesscommunication according to the present disclosure. Figure 4 shows a first antenna 12 and a second antenna 22 in a back-to-back configuration. The transmission directions of antennas 12 and 22 are indicated by the respective arrows.In the illustrated example, antennas 12 and 22 are patch antennas. The antennas 12, 22 aremutually isolated and point in opposite directions. Further, the antennas 12, 22 only transmit forward, but not backwards. Thereby, the RFFE transmits in both directions and receives in most scenarios only from one direction. It can be seen that antennas 12 and 22 are arranged on opposite sides of a substrate 100. The substrate 100 may be, for example, a printed-circuit board. Connectors (not shown) may be provided on the substrate that can be used to connect antenna 12 to a first port of a hybrid coupler and to connect antenna 22 to a second port of a hybrid coupler. In the embodiment shown in Figure 4, it can be seen that antennas 12 and 22 overlap fully, i.e., their respective planar projections on the substrate 100 is the same. However, it is to be notedthat antennas 12 and 22 could also overlap only partially or not at all. It is also possible thateach antenna is provided on its own substrate. Although the previously discussed embodiments and examples of the present invention have been described separately, it is to be understood that some or all of the above-described features can also be combined in different ways. The above discussed embodiments are particularly not intended as limitations, but serve as examples, illustrating features and advantages of the present disclosure.

Claims

CLAIMS1. Device (20) for wireless communication, comprising:a first antenna (12);a second antenna (22); anda hybrid coupler (11) connecting the first antenna (12) to a first transmissionpath (TX1) and the second antenna (22) to a second transmission path (TX2);wherein the first antenna (12) is connected to a first port (2) of the hybrid coupler(11), wherein the second antenna (22) is connected to a second port (3) of the hybridcoupler (11), andwherein the first antenna (12) and the second antenna (22) are arranged in a back-to-back configuration.

2. Device (20) according to claim 1,wherein the hybrid coupler (11) is configured to supply the first antenna (12) with power from the first transmission path (TX1) and the second antenna (22) with power from the second transmission path (TX2) such that a reflection signal from the first antenna (12) is at least partially cancelled by a reflection signal from the secondantenna (22), and vice versa.

3. Device (20) according to any of the preceding claims, wherein the hybrid coupler (11)is a 0 / 180° hybrid coupler.

4. Device (20) according to any of the preceding claims, wherein the first antenna (12) andthe second antenna (22) are of an identical type.

5. Device (20) according to any of the preceding claims, wherein the hybrid coupler (11)further connects the first antenna (12) and the second antenna (22) to a reception path (RX).

6. Device (20) according to any of the preceding claims, comprisinga first antenna array; and a second antenna array; wherein the first antenna array comprises the first antenna (12),wherein the second antenna array comprises the second antenna (22), andwherein the first antenna array and the second antenna array are arranged in a back-to-back configuration.

7. Device (20) according to any of the preceding claims, further comprisinga first antenna tuner (16) arranged between the first port (2) and the first antenna (12); and a second antenna tuner (16) arranged between the second port (3) and the second antenna (22).

8. Device (20) according to claim 6, wherein the first antenna tuner (16) and / or the secondantenna tuner (16) comprise a Chebyshev-type antenna tuner.

9. Method for wireless communication, in particular using a device according to any of thepreceding claims, comprising: supplying a first transmission signal, via a hybrid coupler (11), to a first antenna(12) and a second transmission signal to a second antenna (22);wherein the first antenna (12) is connected to a first port (2) of the hybrid coupler (11), wherein the second antenna (22) is connected to a second port (3) of the hybrid coupler (11), andwherein the first antenna (12) and the second antenna (22) are arranged in a back-to-back configuration; and transmitting the first transmission signal via the first antenna (12) and / or thesecond transmission signal the second antenna (22).

10. Method according to claim 9,wherein the hybrid coupler (11) is configured to supply the first antenna (12)with power from the first transmission path (TX1) and the second antenna (22) with power from the second transmission path (TX2) such that a reflection signal from the first antenna (12) is at least partially cancelled by a reflection signal from the second antenna (22), and vice versa.

11. Method according to any of claims 9 or 10, wherein the hybrid coupler (11) is a 0 / 180°hybrid coupler.

12. Method according to any of claims 9 to 11, wherein the first antenna (12) and the secondantenna (22) are of an identical type.

13. Method according to any of claims 9 to 12, further comprisingadapting, via a first antenna tuner (16) arranged between the first port (2) andthe first antenna (12), an impedance of the first port (2) to match an impedance of thefirst antenna (12); andadapting, via a second antenna tuner (16) arranged between the second port (3) and the second antenna (22), an impedance of the second port (3) to match an impedanceof the second antenna (22).

14. Method according to claim 13, wherein the first antenna tuner (12) and / or the secondantenna (22) tuner comprise a Chebyshev-type antenna tuner.

15. Method according to any of claims 9 to 14, further comprising receiving a signal via thefirst antenna (12) or the second antenna (22).

16. Computer-readable medium comprising instructions which, when executed by acomputer, cause the computer to carry out the method according to any of claims 9 to 15.

Images