Active reflective intelligent surface circuit

Abstract

There is disclosed an active reconfigurable surface (A-RIS) circuit. The A-RIS circuit comprises antenna modules. Each of the antenna modules comprises at least one antenna element, two reflection-NETworks (R-NETs) and a Quadrature-Hybrid Coupler (QHC). Each of the R-NETs comprises a variable negative resistor and a 5 variable reactive component. The variable negative resistor and the variable reactive component are tunable to reflection properties of the A-RIS circuit. The at least one antenna element is coupled to the two R-NETs via the QHC.

Description

[0001] ACTIVE REFLECTIVE INTELLIGENT SURFCE CIRCUIT

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to an active reconfigurable surface circuit, and a radio equipment comprising such an active reconfigurable surface circuit.

[0004] BACKGROUND

[0005] Beamforming has been introduced as part of fifth generation (5G) telecommunication systems. Beamforming can greatly improve the physical layer of the telecommunication system. This is especially prominent in Line-Of-Sight (LOS) communication, but also in Non-Line-Of-Sight (NLOS) communication. However, NLOS communication still provides more challenges than LOS communication, both in the downlink (DL; from network towards user) and the uplink (UL; from user towards network). Reconfigurable Intelligent Surfaces (RIS) have been proposed as a possible technology for sixth generation (6G) telecommunication systems, to improve the communication channel in NLOS communications. An overview of RIS technologies is provided in the paper entitled “Reconfigurable Intelligent Surfaces: Principles and Opportunities,” authored by Y. Liu et al., and published in IEEE Communications Surveys & Tutorials, vol. 23, no. 3, pp. 1546-1577, third quarter 2021, doi: 10.1109 / C0MST.2021.3077737.

[0006] An illustrative example of how an RIS can be used to increase the Quality of Service (QoS) in NLOS scenarios is provided in Fig. 1. In more detail, in Fig. 1 is illustrated a communication network 100 comprised of radio access network nodes 110a, 110b deployed in a metropolitan scenario. In metropolitan areas, skyscrapers and other large buildings 140a: i of create radio shadows, impacting the QoS for the users, as represented by user equipment (UE) 120a, 120b, unless a very dense deployment of radio access network nodes 110a, 110b is used. Hence, most of the communication between the radio access network nodes and the UEs is NLOS, as is the case in the communication between radio access network node 110a and UE 120a. A RIS 130 is used to improve the NLOS communication between radio access network node 110b and UE 120b, especially in the UL. One or more RISs 130 can thus be deployed to reduce the gaps in radio cells, thus extending the coverage area, and increasing the QoS.

[0007] An overview of the RIS concept is illustrated in Fig. 2. In Fig. 2 is schematically illustrated a comparison between a non-configurable reflective surface 200a, wherethe angle of reflection ar is the same as the angle of incidence ai, and a RIS 200b, where the angle of reflection ar is not the same as the angle of incidence ai. As illustrated, the RS 200 can be regarded as exhibiting a controllable surface, used to generate a controllable reflection of radio waves. Two main approaches to implement a RIS will be disclosed next.

[0008] A first approach is to use controllable meta-materials or use an antenna array with controlled passive networks. The meta-material implementation may require exotic materials and may therefore become expensive. On the other hand, an antenna array with controllable passives can be built with off-the-shelf components, at a lower cost than if a meta-material is used. RISs based on either controllable meta-materials and antenna array with controllable passives have inherent losses and thus causes attenuation in the reflected radio waves.

[0009] A second approach is to use a wireless repeater. Wireless repeaters generally require more complex implementation than the aforementioned RIS technologies as wireless repeaters generally require Full-Duplex (FD) functionality. One advantage of the wireless repeater is that a gain can be applied to the signal (thus mitigating or even eliminating any attenuation in the reflected radio waves). Another advantage of the wireless repeater is that the wireless repeater may implement more complex signal processing (in the analog domain) than the aforementioned RIS technologies.

[0010] Wireless repeaters may require isolating functions or components, such as duplexers and / or a Self-Interference Cancellation (SIC) module, in order to separate the incoming radio waves from the outgoing radio waves. This may increase the implementation complexity of the wireless repeaters, even though wireless repeaters do not need to be configured to perform any complex digital-domain signal processing.

[0011] In “Development and Characterization of 5.8 GHz Reflective Amplifier with Variable Gain for Active Reconfigurable Intelligent Surfaces,” authored by G. Collodi, G.

[0012] Lasagni, M. Righini, S. Maddio and A. Cidronali, and published in the proceedings of the 202454th European Microwave Conference (EuMC), Paris, France, 2024, pp. 513-516, is disclosed an active RIS, hereinafter referred to as an A- RIS. A reflective amplifier can be used in order for all the antenna elements in an A- RIS to be utilized.The reflective amplifier is used to drive the antenna impedance, i.e., the impedance based on the active reflection coefficient, if used in an antenna array.

[0013] However, although the A-RIS may represent an advancement in compared to regular RIS (based on either controllable meta-materials, or antenna array with controllable passives, or wireless repeaters) there are still issues with existing RIS technologies.

[0014] For example, A-RIS technologies utilizing the antenna array to generate isolation, limit each antenna element to be used for either beam reception or beam transmission. For example, A-RIS technologies with reflective amplifiers have a gain, which is very dependent on the antenna impedance. This is directly related to the active reflection coefficient.

[0015] SUMMARY

[0016] An object of embodiments herein is to address the above issues.

[0017] A particular object is to provide an A-RIS that maintains all advantages of the aforementioned RIS technologies, but that does not suffer from their disadvantages.

[0018] A particular object is to provide an A-RIS that, based solely on analogue-domain signal processing, provides amplification and the correct impedance for each antenna element in the A-RIS.

[0019] According to a first aspect there is presented an A-RIS circuit. The A-RIS circuit comprises antenna modules. Each of the antenna modules comprises at least one antenna element, two reflection-NETworks (R-NETs) and a Quadrature-Hybrid Coupler (QHC). Each of the R-NETs comprises a variable negative resistor and a variable reactive component. The variable negative resistor and the variable reactive component are tunable to reflection properties of the A-RIS circuit. The at least one antenna element is coupled to the two R-NETs via the QHC.

[0020] According to a second aspect there is presented a radio equipment comprising an active RIS circuit according to the first aspect.

[0021] Advantageously, the disclosed A-RIS circuit provides gain and / or low loss capabilities due to its tunable negative resistors and reactive components within the R-NETs, enabling optimization of the signal performance across the antenna modules.Advantageously, the disclosed A-RIS circuit enables the effect of the antenna elements’ active reflection coefficient to be minimized.

[0022] Advantageously, the disclosed A-RIS circuit enables the channel to be more dynamic compared to a passive RIS.

[0023] Advantageously, channel selectivity of the disclosed A-RIS circuit can be achieved with low-complexity signal processing, such as filtering, which reduces computational demands while maintaining effective and precise signal manipulation.

[0024] Advantageously, the disclosed A-RIS circuit enables lower complexity and hardware requirements than a traditional wireless repeater, making it a cost-effective and compact technology for integration in advanced communication technologies.

[0025] Advantageously, since the disclosed A-RIS circuit does not require down-conversion or up-conversion of the incoming radio signal, no information about the receive signal needs to be digitally stored or processed in a form vulnerable to breaches, making the disclosed A-RIS circuit inherently secure and beneficial for informationsensitive applications.

[0026] Advantageously, the disclosed A-RIS circuit eliminates the need for self-interference cancellation (SIC) mechanisms, simplifying the overall design of the RIS and further reducing hardware and computational requirements of the RIS.

[0027] Advantageously, the disclosed A-RIS circuit has an architecture that supports antenna-in-package technologies or fully integrated implementations.

[0028] Advantageously, the disclosed A-RIS circuit can operate with a combination of gain and / or tapering, offering versatile performance configurations to meet specific needs of different communication scenarios.

[0029] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0030] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc."are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0033] Fig. 1 is a schematic diagram of a communication network according to examples;

[0034] Fig. 2 schematically illustrated a comparison between a non-configurable reflective surface and a RIS according to examples;

[0035] Figs. 3, 4, 5, 6, 7, and 8 are schematic diagrams of antenna modules according to embodiments;

[0036] Fig. 9 is a schematic diagram of an equalizer according to embodiments;

[0037] Fig. io is a schematic diagram of implementation example circuits according to embodiments;

[0038] Fig. n is a schematic diagram of an antenna array according to embodiments;

[0039] Fig. 12 is a schematic diagram of antenna modules according to embodiments;

[0040] Fig. 13 is a schematic diagram of a communication network according to embodiments;

[0041] Figs. 14 and 15 are schematic diagram of radio equipment according to embodiments.

[0042] DETAILED DESCRIPTION

[0043] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0044] According to at least some of the herein disclosed embodiments, there is provided an A-RIS circuit designed to reduce the loss in power and / or to introduce gain to increase the power of signals reflected by the A-RIS. The A-RIS circuit comprises antenna modules, one for each antenna element in the A-RIS circuit.

[0045] Basic forms of an antenna module 300a, 300b, 300c of an A-RIS are shown in Fig.3.

[0046] In the antenna module 300a an antenna element 310 (which generally could be one or more antenna elements, i.e., at last one antenna element) is connected to a controllable active R-NET 320. As above, there is one antenna module per each individual antenna in the RIS circuit. Further, as will be disclosed below, tuning of the components in the R-NET enables the reflection properties (e.g., in terms of gain, loss, frequency, phase, delay, etc.) of the RIS circuit to be changed. The antenna modules 300b, 300c represent differential versions of basic antenna modules. The antenna module 300b is using a differential antenna 310’ (or “dipole”) and the antenna module 300c is using a balun circuit TBaiun. The antenna modules 300b, 300c represent embodiments where the at least one antenna element is differential-ended and comprises two differential coupling ports. These antenna module 300a, 300b, 300c are just some illustrative and non-limiting examples of basic antenna modules and other implementations are also possible.

[0047] One drawback of the antenna modules 300a, 300b, 300c in Fig. 3 is the gain to stability relations, especially when the antenna impedance is mismatched, i.e. deviates from the ideal nominal impedance Zo. Therefore, if the gain in the system is more than the power of the antenna reflections, the system loses stability, due to the negative resistance. This can be addressed by reducing the reflections that reaches the R-NET, as in Fig. 4. In Fig. 4 is illustrated two embodiments of an antenna module 400a, 400b of an A-RIS. In this respect, an antenna module 400a represents a single-ended version with one QHC 410 and antenna module 400b represents a differential version with a balun, which thus requires two QHCs 410a, 410b. Both antenna modules 400a, 400b are based on having the antenna element coupled to two R-NETs via a respective QHC. The antenna module 400b represents anembodiment where the antenna module comprises two QHCs, and where each of the two differential coupling ports is coupled to the two R-NETs via a respective one of the two QHCs.

[0048] The QHC comprises an input port (denoted “Input port” or “Port 1”) and two output ports (denoted “THRU Port” or “Port 2” and “CPL Port” or “Port 3”), and an isolated port (denoted “ISO Port” or “Port 4”). The at least one antenna element is coupled to the input port, and each of the two R-NETs is coupled to a respective one of the output ports. In the embodiments in Fig. 4, the isolated port of the QHC is connected to a termination impedance Zoand the remaining ports are connected to the antenna and to two R-NETs, denoted R-NETi and R-NET2. That is, the antenna module may further comprise at least one termination impedance element Zo, where the isolated port is coupled to the termination impedance element. Equivalently, the the isolated port is coupled to a termination impedance element equivalent to the characteristic impedance of the QHC. In these ways, variations of antenna impedance can be compensated by the QHC. For example, in some cases, the impedance deviates from Zoo, the termination impedance connected to the ISO port, this means that the impedance seen by R-NETi is increased or decreased, and the impedance seen by R-NET2is decreased or increased. This results in a system gain with very small dependency on the antenna impedance.

[0049] Each of the R-NETs comprises a variable negative resistor and a variable reactive component. In general terms negative resistance implies that when the voltage increases, the current also increases, but with a negative polarity. Thus, when voltage increase, then the negative resistance adds energy to the circuit. The variable negative resistor and the variable reactive component are tunable to reflection properties of the A-RIS circuit. The R-NETs can be implemented by active and passive components. Reference is next made to Fig.5 in which is illustrated antenna modules 500a, 500b, 500c, sood with different realizations of R-NETs, both for the basic antenna module 300a in Fig. 3 and for the antenna module 400a in Fig, 4. Antenna modules 500a, 500c represent implementations where each R-NET is realized using a variable negative resistance (-R, -Ri, -R2) and a variable impedance (Z, Zi, Z2), and antenna modules 500b, sood represent implementations where each R-NET is realized with a variable negative resistance (-R, -Ri, -R2) and a variable capacitor (C, Ci, C2). However, these examples represent just some possibleimplementations. By using a low complexity R-NET, the available variation in phaseshift, or delay, is limited to 90 degrees, or 0.25TRF, where TRF is the period of the radio-frequency carrier of the signal to be reflected by the A-RIS circuit.

[0050] To extend the range of the variable phase-shift, or delay, either more complex structures in the R-NET can be used, or a phase shifter, or delay-line, can be introduced between the antenna element and the QHC, or between the antenna element and the R-NET, as illustrated in Fig. 6. That is, in some embodiments, each of the antenna modules further comprises at least one of: a phase shifter and a time delay element coupled between the at least one antenna element and the QHC. In Fig. 6 is illustrated antenna modules 600a, 600b, 600c, 6ood with different realizations of phase shifters, or delay-lines. Antenna module 600a represents an example of a basic antenna module where a phase shifter 610 is coupled between the antenna element and the R-NET. Antenna module 600b represents an example of a basic antenna module where a delay-line 620 (being an example of a time delay element) is coupled between the antenna element and the R-NET. Antenna module 600c represents an implementation where a phase shifter is coupled between the antenna element and the QHC. Antenna module 6ood represents an implementation where a delay-line is coupled between the antenna element and the QHC.

[0051] A feed-forward structure, such as a feed-forward amplifier structure, can be used to further improve flexibility, fidelity, gain, stability, and control of the antenna modules, as illustrated in Fig. 7. In Fig. 7 is illustrated antenna modules 700a, 700b, 700c with different realizations of feed-forward amplifier structures 710, 710a, 710b. The antenna modules 700a, 700b, 700c thus further comprise a feed-forward structure, where the feed-forward structure is coupled between the two R-NETs and the isolated port. The feed-forward amplifier structure may implement any of the following features: variable gain, variable attenuation, signal-inversion (signswapping), phase-shift, or delay, filtering, etc. In antenna modules 700a, 700b, the output impedance of the feed-forward amplifier structure is used to replace the Zo termination at the ISO port of the QHC. In this way the antenna modules 700a, 700b can be impedance tuned to the antenna element. Generally, the current amplitude and phase affect the apparent impedance at the CPL and THRU ports. In more detail, the incoming wave is reflected at the CPL and THRU ports and reaches termination at the ISO port. If the impedance of the ISO port matches the antenna impedance, theinput matching will be good and the incoming wave is dissipated there. The total power transmitted towards the antenna is the sum of the power injected at the CPL, THRU, and ISO ports. The feed-forward structure may comprise at least one amplifier and at least one of: a phase shifter and time delay element. In antenna module 700a a feed-forward amplifier is coupled between the two R-NETs and the ISO port of the QHC via a phase shifter. The antenna module 700b uses a second QHC, connected to the outputs of the two R-NETs, to align the phases to reduce the gain reduction. Also, in antenna module 700b, the second QHC is connected to a terminating impedance Zo as well as to a feed-forward amplifier via a phase shifter. A feed-forward amplifier is coupled between phase shifter and the ISO port of the first QHC. The antenna module 700c comprises a second QHC coupled at the outputs of two feed-forward amplifiers. This antenna module 700c can implement a full 4-quadrant vector-modulator. Further, the output of the antenna module 700a that is connected to the ISO port, the output signal only directly couples to -Ri and Zi, and the port connected to -R2 and Z2is isolated from the output of the amplifier. This means that for a specific gain and phase setting of the amplifier, an isolated state can be generated at the port connected to -Ri and Zi by selecting specific values for -Ri and Zi. As a result, the main functionality of the antenna module is set by the values of -R2, Z2, and the gain and phase of the amplifier.

[0052] In some embodiments, the antenna module further comprises a band pass filter (or other type of input filtering structure) coupled between the at least one antenna element and the QHC. Fig. 8 illustrates embodiments of antenna modules 800a, 800b where an input filtering structure 810 is coupled between the antenna element and the R-NET (as for antenna module 800a) or between the antenna element and the QHC (as for antenna module 800b). The input filtering structure can be of any technology, such as Surface Acoustic-Wave (SAW), Bulk Acoustic-Wave (BAW), RLC filter, etc. One advantage of using such an input filtering structure is to reduce noise and amplification of unwanted out-of-band signals (e.g. blockers). Filtration can also be implemented in the R-NET. In this case, the filter can be implemented by active filters, such as for example N-Path filters, Gm-C filters, etc.

[0053] Another way is to, for example, use an equalizer, but modifying it with negative resistances (to introduce gain), as in Fig. 9. That is, in some embodiments, the band pass filter is an equalizer 900, where the equalizer 900 comprises at least oneequalizer stage, and each equalizer stage comprises a variable negative resistor and a variable reactive component. In Fig. 9 is illustrated an equalizer 900 according to embodiments. The equalizer 900 is implemented in two R-NETs and comprises tapped inductors Lil, L21, L31, L12, L22, L32 (with switch functionality) for gain tuning, variable impedances Z11, Z21, Z31, Z12, Z22, Z32 to set the passband frequency, and variable negative resistances -R11, -R21, -R31, -R12, -R22, -R32 for gain and quality factor (Q) tuning defined as FRF / BW, where BW is the 3-dB bandwidth, and FRF is the radio frequency being adjusted. The equalizer further comprises individual variable delay lines D11, D21, D31, D12, D22, D32 to beam steer each individually channel, or frequency band. One benefit of using an equalizer 900 is that individual channels, or frequency bands, can be tuned differently with regards to gain, Q, frequency, and phase-shift, and / or delay.

[0054] Three implementation example circuits 1000a, 1000b, 1000c of the negative resistance are shown in Fig. 10. The circuit 1000a is a single-ended Colpitts negative-resistance and comprises an active device M represented by a metal-oxide-semiconductor field-effect transistorfbut can be any type of semiconductor technology) with its gate connected to a bias voltage Vb (to control the negative resistance), an RF choke (RFC) as a current-source, a feedback network comprising the capacitors Ci, C2, and inductor Li. In this respect, Ci, C2, and Li, can also be tunable. The circuit 1000b is a differential cross-coupled pair with gate-bias and comprises cross-coupled active devices Mi, M2, and high pass filters C, R, connected to a bias voltage Vb (to control the negative resistance). The circuit 1000c is a differential cross-coupled pair with a Tail current-source and comprises crosscoupled active devices M2, and a Tail current-source, i.e. an active device Mi, and where a negative resistance is controlled by a bias voltage Vb. Furthermore, if perfect quadrature phases between the signals at R-NETi and R-NET2 is required, then circuits for quadrature circuits may be used. A further implementation of the negative-resistance is the use of a Tunnel Diode (TD) and / or a Resonant -Tunneling Diode (RTD). To implement the accompanying impedance (Z) of the R-NET, either transformers, switched circuits like switched-transformers, switched-inductors, switched-resistors, and / or switch-capacitors can be used, but also varactors and other variable impedances in different semiconductor materials, to just name a few.The antenna modules may collectively constitute an antenna array. This antenna array may have either single polarity or dual polarity. An example of an antenna array noo with dual polarity is illustrated in Fig. 11. The antenna array noo comprises eight dual-polarized antenna elements mo. In this example, there are thus 16 antenna modules in total, where each antenna module is individually controlled. This enables the possibility to reflect beams in most directions (-7I<0<TI) and also the ability to generate beams and nulls in the reflections.

[0055] As will be further disclosed below, the antenna modules, and thus the antenna array noo, may be part of a radio equipment. Further, the signal to be reflected by the A-RIS circuit might be coming from different types of radio equipment. Depending on the type of radio equipment from which the signal is received, also the received power levels can be expected to vary significantly. In case the radio equipment from which the signal is received is a UE, the aforementioned feed-forward structure can be used to extend the useful range of the A-RIS. case the radio equipment from which the signal is received is a radio access network node, the aforementioned feed-forward structure may be turned off or have reduced gain settings in order to not distort the received signal. As in the embodiments of antenna modules 1200a, 1200b in Fig. 12, for optimal performance and gain settings, either some communication with radio access network node (as for antenna module 1200a) or some internal tracking of received power levels in the A-RIS circuit (as for antenna module 1200b) could be used. In further detail, both antenna modules 1200a, 1200b comprise a controller (CTRL) 1210. The controller is configured to receive a control signal pertaining to the reflection properties of the active RIS circuit and to set a resistance of the variable negative resistor and an impedance of the variable reactive component of the R-NETs in each of the antenna modules in accordance with the control signal. According to the antenna module 1200a the controller is configured to receive the control signal over a wireless interface. For antenna module 1200a, which is based on using backhaul control, most of the control and computation can be performed by the radio access network node and the antenna module 1200a only needs to implement interna control. The antenna module 1200b further comprises a peak detector (PD) 1220. The peak detector is coupled to an interface between the at least one antenna element and the QHC. The peak detector is configured to detect peaks in signals received bythe at least one antenna element, to convert the detected peaks into the control signal, and to provide the control signal to the controller.

[0056] Any of the herein disclosed A-RIS circuits may be part of a radio equipment. This is schematically illustrated in Fig. 13 and in Fig. 14. in Fig. 13 is illustrated a communication network 1300 comprised of radio access network nodes 1310a, 1310b deployed in a metropolitan scenario and serving UEs 1320a, 1320b, 1320c, I32od. UEs 1320a, 1320b are served by radio access network node 1310a and UEs 1320c, i32od are served by radio access network node 1310b.

[0057] For illustrative purposes it is assumed that UE 1320b is in radio shadow with respect to its serving radio access network node 1310a and that UE I32od is in radio shadow with respect to its serving radio access network node 1310b. This might negatively affect the radio quality of UE 1320b and UE i32od, possibly even causing service disruptions. However, for illustrative purposes it is further assumed that UE 1320c comprises any of the herein disclosed A-RIS circuits. UE 1320c may therefore assist UE I32od with respect to coverage. In particular, the A-RIS circuit in UE 1320c may be used to reflect signals (or radio waves) between radio access network node 1310b and UE I32od, thereby enabling UE I32od to maintain network connection. In this way, LOS communication can be used for UE I32od whilst also reducing the output power of radio access network node 1310b.

[0058] There could be different types of implementations of A-RIS circuits in the radio equipment. Two examples are illustrated in Fig. 14. In Fig. 14 is illustrated a radio equipment 1400a, 1400b comprising an A-RIS circuit (as represented by a single antenna module) as herein disclosed. In the radio equipment 1400b, a switch (SW) 1430 is provided in the antenna module to selectively connect the antenna element to either the rest of the antenna module 1410 (comprising QHC, R-NETs, etc.) or a transceiver 1420 of the radio equipment 1400b. Radio equipment 1400a thus represents a standalone version of the A-RIS circuit whereas radio equipment 1400b represents an example where the A-RIS circuit (or at least its antenna modules) is integrated with a transceiver (TRX), separated by a switch. Hence, in some embodiments, at least some of the antenna modules further comprises a switch, and the switch is configured to selectively connect the antenna to either the QHC or one ofthe transceivers of the radio equipment. In this way, the herein disclosed antenna modules can be selectively enabled and disabled.

[0059] There could be different types of radio equipment, such as radio access network nodes or UEs. For example, the radio equipment 1400a could be part of a radio access network node. For example, the radio equipment 1400b could be part of a user equipment. In general terms, the radio access network node could be any of a radio base station, base transceiver station, node B (NB), evolved node B (eNB), gNB, access point, access node, transmission and reception point (TRP), integrated access and backhaul (IAB) node, etc. Likewise, the UE could be any of a portable wireless device, mobile station, mobile phone, handset, wireless local loop phone, smartphone, laptop computer, tablet computer, wireless modem, wireless sensor device, network equipped vehicle, Internet of Things (loT) device, game controller, etc.

[0060] In Fig. 15 is illustrated a front view of an example where the A-RIS circuit (or at least its antenna modules 1520) is implemented in combination with transceivers (TRX) 1510 of the radio equipment 1500. In this example, the radio equipment thus further comprises transceivers and at least one antenna elements not coupled to any of the antenna modules. This could be the case where the A-RIS circuit is part of a radio access network node. The leakage between the antenna elements can be amplified by the antenna modules and if the gain is equal to the element-to-element isolation, then the effective Equivalent Isotropic Radiated Power (EIRP) is increased by approx. 2-3 dB without increasing the amount of transceiver hardware in the radio equipment.

[0061] In summary, according to at least some of the herein disclosed embodiments, there has been disclosed an A-RIS circuit comprising antenna modules, where at least one antenna element is coupled to two R-NETs and QHC. Each of the R-NETs comprises a variable negative resistor and a variable reactive component configured to tune the gain, or loss, the frequency, and the phase, or delay of the signal to control properties of the wanted reflection. The QHC can be either with and without a feed-forward structure. The QHC improves the flexibility, the possible gain, and the stability of the A-RIS circuit. To increase the amount of phase, or delay, a phase shifter and / or a time delay element can be coupled between the at least one antenna and the other components of the antenna modules. For even more flexibility, fidelity, control, andgain, a feed-forward structure with variable gain and / or phase, or delay, can placed coupled the ISO port of the QHC and the two R-NETs. A filtering structure can be used to reduce out-of-band effects, such as noise and amplification of out-of-band blockers. The inherent advantage of negative-resistance circuits is the narrow banding (due to Q-value boosting) effect of resonators, and the used resonators ranges from single-order- to multi-order-resonators. Each antenna element is placed in an antenna array, either with a single polarity or dual polarity.

[0062] A radio access network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that radio access network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, the radio access network node may be an open radio access network (ORAN) network node. An ORAN network node is a radio access network node that supports an ORAN specification (e.g., a specification published by the 0-RAN Alliance, or any similar organization) and may operate alone or together with other radio access network nodes to implement one or more functionalities of any radio access network node, including one or more radio access network nodes and / or core network nodes. Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU-CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). An ORAN network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wi, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN network node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the O-RAN Alliance or comparable technologies.The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

1. CLAIMS1. An active reconfigurable intelligent surface, RIS, circuit (200b), wherein the active RIS circuit (200b) comprises antenna modules (400a: 800b, 1200a, 1200b), and wherein each of the antenna modules (4ooa:8oob, 1200a, 1200b) comprises:at least one antenna element;two reflection-NETworks, R-NETs, wherein each of the R-NETs comprises a variable negative resistor and a variable reactive component, where the variable negative resistor and the variable reactive component are tunable to reflection properties of the active RIS circuit (200b); anda Quadrature-Hybrid Coupler, QHC, wherein the at least one antenna element is coupled to the two R-NETs via the QHC.

2. The active RIS circuit (200b) according to claim 1, wherein the QHC comprises an input port and two output ports, wherein the at least one antenna element is coupled to the input port, and wherein each of the two R-NETs is coupled to a respective one of the output ports.

3. The active RIS circuit (200b) according to claim 1 or 2, wherein the QHC further comprises an isolated port.

4. The active RIS circuit (200b) according to claim 3, wherein each of the antenna modules (400a: 800b, 1200a, 1200b) further comprises a termination impedance element, and wherein the isolated port is coupled to the termination impedance element.

5. The active RIS circuit (200b) according to claim 3, wherein the QHC has a characteristic impedance, and wherein the isolated port is coupled to a termination impedance element equivalent to the characteristic impedance of the QHC.

6. The active RIS circuit (200b) according to any preceding claim, wherein the at least one antenna element is differential -ended and comprises two differential coupling ports, and wherein each of the antenna modules (4ooa:8oob, 1200a, 1200b) comprises two QHCs, and wherein each of the two differential coupling ports is coupled to the two R-NETs via a respective one of the two QHCs.7- The active RIS circuit (200b) according to any preceding claim, wherein each of the antenna modules (400a: 800b, 1200a, 1200b) further comprises at least one of a phase shifter and a time delay element coupled between the at least one antenna element and the QHC.

8. The active RIS circuit (200b) according to claim 3 or 4, wherein each of the antenna modules (4ooa:8oob, 1200a, 1200b) further comprises a feed-forward structure, wherein the feed-forward structure is coupled between the two R-NETs and the isolated port.

9. The active RIS circuit (200b) according to claim 8, wherein the feed-forward structure comprises at least one amplifier and at least one of: a phase shifter and time delay element.

10. The active RIS circuit (200b) according to any preceding claim, wherein each of the antenna modules (400a: 800b, 1200a, 1200b) further comprises a band pass filter coupled between the at least one antenna element and the QHC.

11. The active RIS circuit (200b) according to claim 10, wherein the band pass filter is an equalizer (900), where the equalizer (900) comprises at least one equalizer stage, and wherein each equalizer stage comprises a variable negative resistor and a variable reactive component.

12. The active RIS circuit (200b) according to any preceding claim, wherein the antenna modules (4ooa:8oob, 1200a, 1200b) collectively constitute an antenna array (1100), and wherein the antenna array (1100) has either single polarity or dual polarity.

13. The active RIS circuit (200b) according to any preceding claim, wherein the active RIS circuit (200b) further comprises:a controller, wherein the controller is configured to receive a control signal pertaining to the reflection properties of the active RIS circuit (200b) and to set a resistance of the variable negative resistor and an impedance of the variable reactive component of the R-NETs in each of the antenna modules (400a: 800b, 1200a, 1200b) in accordance with the control signal.14- The active RIS circuit (200b) according to claim 13, wherein the controller is configured to receive the control signal over a wireless interface.

15. The active RIS circuit (200b) according to claim 13, wherein each of the antenna modules (4ooa:8oob, 1200a, 1200b) further comprises:a peak detector, wherein the peak detector is coupled to an interface between the at least one antenna element and the QHC, and wherein the peak detector is configured to detect peaks in signals received by the at least one antenna element, to convert the detected peaks into the control signal, and to provide the control signal to the controller.

16. A radio equipment (1400a, 1400b, 1500) comprising an active RIS circuit (200b) according to any preceding claim.

17. The radio equipment (1400a, 1400b, 1500) according to claim 16, wherein at least some of the antenna modules (400a: 800b, 1200a, 1200b) further comprises a switch, wherein the radio equipment (1400a, 1400b, 1500) further comprises transceivers, and wherein the switch is configured to selectively connect the antenna to either the QHC or one of the transceivers.

18. The radio equipment (1400a, 1400b, 1500) according to claim 17, wherein the radio equipment (1400a, 1400b, 1500) is part of a user equipment.

19. The radio equipment (1400a, 1400b, 1500) according to claim 16, wherein the radio equipment (1400a, 1400b, 1500) further comprises transceivers and at least one antenna elements not coupled to any of the antenna modules (4ooa:8oob, 1200a, 1200b).

20. The radio equipment (1400a, 1400b, 1500) according to claim 19, wherein the radio equipment (1400a, 1400b, 1500) is part of a radio access network node.

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