Triple-band antenna and transceiver device

Abstract

There is provided a triple-band leaky-wave antenna for a transceiver device. The triple-band leaky-wave antenna comprises an antenna structure. The antenna structure comprises at least one antenna element. The antenna structure is configured to operate in three frequencies. The triple-band leaky-wave antenna further comprises a one-layer metasurface. The one-layer metasurface is arranged to face the at least one antenna element. The one-layer metasurface is placed at a distance on top of the antenna structure. The metasurface has a frequency-dependent impedance yielding different reflection properties for the three frequencies.

Description

[0001] TRIPLE-BAND ANTENNA AND TRANSCEIVER DEVICE

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a triple-band leaky-wave antenna for a transceiver device, and a transceiver device comprising such a triple-band leaky-wave antenna.

[0004] BACKGROUND

[0005] Advanced telecommunication systems, such as the fifth generation (5G) advanced systems, improve performance over existing telecommunication systems with respect to capacity, bandwidth, etc. and thereby provide new scenarios for novel communication applications. However, such advanced telecommunication systems also pose new challenges, for example with respect to antenna systems and other radio frequency components. For example, advanced telecommunication systems require antenna systems with increasingly higher gains to compensate for the path losses resulting from high-frequency operations (e.g., in frequency bands above 10 GHz). In this respect, antenna systems with phased- array antennas may provide the required antenna gain at the cost of having a large amount of radiating elements. In turn, in addition to the antenna systems having large physical dimensions, this also implies a high cost in terms of active components (i.e., power amplifiers, phase shifters, etc.) for operating the antenna systems. Further, the new available frequency bands and the increased bandwidths also raises a need for the network equipment (including the antenna systems) to be configured for multiband operation.

[0006] Hence, there is a need for providing antenna arrays with high gain but few control points.

[0007] One approach is to use large sub-arrays or large spacing between the phased array elements in the antenna systems. Unfortunately, fewer control points (implying larger sub-arrays or element spacing, for example an element spacing larger than 1 / 2, where A is the wavelength) excite higher order modes, in turn yielding the appearance of grating lobes. Several approaches have been proposed to attenuate the grating lobes but they generally compromise some aspect of the antenna performance. Another disadvantage of using large sub-arrays is the higher losses related to the feeding network that group the elements in the sub-array. An alternative to having large sub-arrays is therefore to use leaky-wave antennas to increase the gain of low-gain antenna systems. Here, the obtained gain comes from an enlarged antenna aperture that is analog to using large sub-arrays but avoids the feeding network. One example of a design methodology for a leaky-wave antenna can be found in “Design methodology of single-layer dual-band metasurfaces for leaky- wave antennas” by N. Memeletzoglou and D. Blanco Montero, published in IEEE Transactions on Antennas and Propagation, vol. 71, no. 2, pp. 1196-1203, 2023.

[0008] However, existing leaky-wave antennas for multiband (i.e., more than two frequency bands) have high complexity in terms of requiring two or more metasurface layers, resulting in bulky antenna systems, a complicated design process, as well as high manufacturing costs.

[0009] Hence, there is a need for improved leaky-wave antennas.

[0010] SUMMARY

[0011] An object of embodiments herein is to provide leaky-wave antennas that do not suffer from the above issues.

[0012] A particular object is to provide a leaky-wave antenna that requires only a single metasurface layer, but still is capable of providing multiband operation.

[0013] According to a first aspect there is presented a triple-band leaky-wave antenna for a transceiver device. The triple-band leaky-wave antenna comprises an antenna structure. The antenna structure comprises at least one antenna element. The antenna structure is configured to operate in three frequencies. The triple-band leaky-wave antenna further comprises a one-layer metasurface. The one-layer metasurface is arranged to face the at least one antenna element. The one-layer metasurface is placed at a distance on top of the antenna structure. The metasurface has a frequency-dependent impedance yielding different reflection properties for the three frequencies.

[0014] According to a second aspect there is presented a transceiver device. The transceiver device comprises a triple-band leaky-wave antenna according to the first aspect.

[0015] Advantageously, this triple-band leaky-wave antenna does not suffer from the above issues. Advantageously, with this triple-band leaky-wave antenna, the grating lobes are efficiently attenuated.

[0016] Advantageously, this triple-band leaky-wave antenna offers both a simple implementation (e.g., only requiring one metasurface layer) and gain versatility, translating to a low cost for the triple-band leaky-wave antenna.

[0017] 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.

[0018] 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.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0021] Fig. 1 is a schematic diagram illustrating a reference antenna structure according to an example;

[0022] Fig. 2 shows simulation results according to an example;

[0023] Fig. 3 is a schematic diagram illustrating a triple-band leaky-wave antenna and transceiver device according to an embodiment;

[0024] Fig. 4 is a schematic diagram illustrating a unit cell of the triple-band leaky-wave antenna according to an embodiment;

[0025] Fig. 5 shows characteristics of a frequency-dependent impedance; and

[0026] Fig. 6 shows simulation results according to an embodiment. DETAILED DESCRIPTION

[0027] 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 to those 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.

[0028] A reference benchmark antenna structure loo is illustrated in Fig 1. The antenna structure too comprises antenna elements 120, provided in an array 110. Without loss of generality, the antenna structure 100 is composed of 4-by-4 single-polarized radiating elements, but the design can be used in the same way with dual-polarized or circular-polarized elements, or even with a single radiating antenna element. For simplicity, the radiating element is illustrated as a planar dipole excited by a coupled slot. The overall stack-up of the antenna structure 100 is also depicted in Fig. 1. The antenna elements 120 are separated by a distance P. For example, P = 1.64 ■ A for a carrier frequency of 23 GHz and P = 2.05 ■ A for a carrier frequency of 28.75 GHz. As will be further disclosed below, in the disclosed triple-band leaky-wave antenna, the chosen period reduces the number of required antenna elements for the same performance by a factor of 4 (i.e. , from 64 antenna elements in an antenna array with a P= A / 2, to 16 antenna elements in the current example), whilst not requiring any sub-array feeding network.

[0029] By itself, the presented reference benchmark antenna structure 100 suffers from two drawbacks. A first drawback is the inevitable grating lobes radiating to a different angle than the main lobe. A second drawback is the loss of gain in the main beam due to the grating lobes. In general terms, grating lobes represent a phenomena that occurs as the pitch between neighboring antenna elements exceed A / 2, and thus resembles a spatial Nyquist sampling effect for antennas where the main lobe have spatial copies in the visible frequency range. As an example, the radiation patterns for the carrier frequencies 23 GHz and 28.75 GHz are shown in Fig. 2 for the H-plane (i.e., the magnetic field plane). Similar results are obtained for the E-plane (i. e. , the electric field plane). Grating lobes are clearly visible in Fig. 2, for example approximately at ± 30 deg for the radiation pattern of the 28.75 GHz signal. As the magnitude of the grating lobe depends on the inter-element space (and for a fixed period as in the example), higher frequencies imply grating lobes closer to the main lobe. This is also visible in Fig. 2 since the grating lobes of the radiation pattern of the 28.75 GHZ signal are closer to the main beam than the grating lobes of the radiation pattern of the 23 GHz signal. In this respect, the closer to the main beam the grating lobes are, the more similar beamwidth they have, which implies that the grating lobes in principle will have identical radiation power as the main lobe.

[0030] A triple-band leaky-wave antenna and a transceiver device comprising such a tripleband leaky-wave antenna will hereinafter be disclosed that can be used to combat these issues.

[0031] In some aspects, the design of the triple-band leaky-wave antenna is based on a single metasurface layer, allowing the triple-band leaky-wave antenna to have a low profile and low cost, whilst at the same providing a versatile antenna for use in advanced telecommunication systems with multiband operation. Having a single-layer metasurface offers two operational high-gain frequency bands; a low frequency band (LB) and high frequency band (HB), respectively, as well as a middle frequency band (MB) where the metasurface is transparent and does not yield any antenna gain. The MB can be used in some scenarios as a control channel. The different frequency bands will below be represented by their respective frequencies, denoted fl, f2, f3, where fl thus corresponds to the low frequency band, f2 corresponds to the middle frequency band, and f3 corresponds to the high frequency band. Further, the metasurface acts as a frequency selective surface (i.e., stop band) for the frequencies below and above the passband.

[0032] Reference is next made to Fig. 3 in which a triple-band leaky-wave antenna 310 for a transceiver device 300 is illustrated. In Fig. 3, the triple-band leaky-wave antenna 310 is schematically illustrated as being part of a transceiver device 300. Examples of transceiver devices 300 will be disclosed below. The triple-band leaky-wave antenna 310 comprises an antenna structure 320. The antenna structure 320 comprises at least one antenna element 120.

[0033] There could be different types of antenna structures 320, for example as illustrated in Fig. 1 and disclosed with reference to Fig. 1. In some embodiments, as illustrated in Fig. 1, the antenna structure 320 comprises an array of at least three antenna elements 120. However, in other embodiments, the antenna structure 320 comprises only one single antenna element 120.

[0034] In any case, the antenna structure 320 is configured to operate in the three frequencies fl, f2, f3. For example, in case the antenna structure 320 comprises an array of at least three antenna elements 120, each of the antenna elements might be configured to operate in a respective one of the three frequencies fl, f2, f3. In this respect, the antenna structure 320 might comprise a first group of antenna elements configured to operate in frequency fl, a second group of antenna elements configured to operate in frequency f2, and a third group of antenna elements configured to operate in frequency f3. However, in other aspects, one of more of the antenna elements might be configured, or controlled, to operate in two or more frequencies, but only in one frequency per time. Hence, one and the same antenna element might be controlled to operate in frequency fl during some time interval and in frequency f2 during some other time interval, etc. The disclosed triple-band leaky-wave antenna 310 can thus be used for an antenna structure 320 with one a single antenna element as well as for an antenna structure with a phased array antenna, producing the same triple band effect, increasing the effective antenna aperture and thus the gain.

[0035] The triple-band leaky-wave antenna 310 further comprises a one-layer metasurface 330. The metasurface 330 has a frequency-dependent impedance, yielding different reflection properties for the three frequencies fl, f2, f3.

[0036] In some aspects, the metasurface 330 provides high gain for two frequency bands. Particularly, in some embodiments, according to the reflection properties, the metasurface 330 is configured to amplify a radiated field of the at least one antenna element 120 for exactly two frequencies, fl, f3, of the three frequencies fl, f2, f3. In some aspects, the metasurface 330 provides the same gain as the reference benchmark antenna structure for one frequency band. Particularly, in some embodiments, according to the reflection properties, the metasurface 330 is transparent to a radiated field of the at least one antenna element 120 for only a single one frequency, f2, of the three frequencies fl, f2, f3. The frequencies fl, f2, f3 might thus for this purpose corresponds to the above-disclosed low frequency band, middle frequency band, and high frequency band, respectively, where thus fl < f2 < f3. Further aspects of the reflection properties will be disclosed below with reference to Fig. 5. In some aspects, the metasurface 330 serves as a stopband filter for frequencies below fl and above f3.

[0037] The one-layer metasurface 330 is facing the at least one antenna element 120. The one-layer metasurface 330 is placed at a distance h on top of the antenna structure 320. A gap, or cavity, of height h is thereby created between the antenna structure 320 and the metasurface 330. The cavity can be regarded as a Fabry-Perot cavity. Once the metasurface 330 is placing on top of the antenna structure to create a cavity, the antenna elements excite a field that is partially trapped and radiated along the metasurface 330 over the whole antenna aperture. In general terms, there might be different numerical values of the distance h, for example depending on the desired properties of the triple-band leaky-wave antenna 310, the values of the three frequencies fl, f2, f3, etc. In some non-limiting examples, the distance h is contained within a distance interval extending from 2 mm to 10 mm, preferably from 4 mm to 8 mm.

[0038] In general terms, the metasurface 330 might be provided either as a separate component of the triple-band leaky-wave antenna 310 or be provided in, or integrated with, a further component of the triple-band leaky-wave antenna 310. For example, if the triple-band leaky-wave antenna 310 is provided with a radome 340, the metasurface 330 could be embedded in the radome 340. This allows for a compact design of the design of the triple-band leaky-wave antenna 310, as well as protecting the metasurface 330.

[0039] Reference is next made to Fig. 4, in which is illustrated a unit cell 400 of the metasurface 330.. The illustrated unit cell 400 is a double square loop, but any other unit cells fulfilling certain conditions can be used. One condition is that the periodicity of the metasurface (as defined by the length 1 of the unit cell 400) is lower than 1 / 4. One condition is that the unit cell gives the metasurface a resonant frequency around f2. One condition t is that the unit cell gives the metasurface an inductive impedance at fl and a capacitive impedance at f3.

[0040] In general terms, in a classical leaky-wave antenna, a partially reflecting surface can be synthesized with a dielectric slab or with a metasurface that has an impedance as constant as possible. However, one key of having a multiband leaky-wave antenna 310 is the resonant behavior of the metasurface. Reference is here made to Fig. 5 which shows characteristics of a frequency-dependent impedance 500 of the metasurface. As it can be seen in Fig. 5, the impedance switches from being inductive at low frequencies to being capacitive at higher frequencies, with an interval there between where the impedance is undefined. For the region where the metasurface is inductive, a relatively small electrical cavity (i.e., a relatively small value of h) is needed, whilst for the region where the metasurface 330 is capacitive, a relatively large electrical cavity (i.e., a relatively large value of h) is needed. This naturally occurs for the herein disclosed leaky-wave antenna, where the distance h, in electrical sense, seems to be relatively smaller at low frequencies but relatively larger at high frequencies. It is here understood that different metasurfaces will have different characteristics, and that the characteristics shown in Fig. 5 therefore only represents one illustrative example. For example, in the example of Fig. 5 the metasurface has an impedance of a relatively large (or even undefined) magnitude for frequencies ranging from 26.5 GHz to 27.5 GHz, indicating that the leaky-wave modes are barely excited, and the metasurface in this frequency interval appears to be transparent to the radiated fields of the antenna elements. This phenomenon can be exploited to create more advance applications as the phased array or single antenna elements of will radiate in this middle frequency band. Further, for the characteristics shown in Fig. 5, the impedance has a faster variation in the higher frequencies (above 27.5 GHz) compared to the lower frequencies (below 26.5 GHz) and this translates to a smaller bandwidth at the high frequencies. However, as noted above, the characteristics maybe different for different metasurfaces. In any case, in some embodiments, according to the reflection properties, the frequency-dependent impedance 500 is inductive for frequency fl, the frequency-dependent impedance 500 is infinite, or undefined, for frequency f2, and the frequency-dependent impedance 500 is capacitive for frequency f3. In some examples, all the three frequencies fl, f2, f3 are contained within a frequency interval extending from 15 GHz to 35 GHz.

[0041] Simulation results will be disclosed next with reference to Fig. 6. The simulation results are shown for two frequency bands in the range of 20 to 30GHz, namely 23 GHz and 28.75 GHz, but other frequency bands can be synthesized by a compromise in terms of gain versus bandwidth. With reference to Fig. 5, for the specific frequency bands, f=23 GHz and f=28.75 GHz the impedance values of the metasurface are 156! and -222i, respectively. The metasurface was placed on top of the reference benchmark antenna structure at distance h = 5.79 mm. Fig. 6 shows radiation patterns for the H-plane (i.e. , the magnetic field plane). Similar results are obtained for the E-plane (i.e., the electric field plane). In comparison to Fig. 2, it is clear that the grating lobes are attenuated at least to the level of the side lobes (to about -13 dBi with respect to the main lobe) and that this energy is recovered into the main lobe. The main lobes in Fig. 6 have a maximum gain of 26.6 dBi and 28.2 dBi for f= 23 GHz and f = 28.75 GHz respectively.

[0042] The use of one single metasurface layer makes the triple-band leaky-wave antenna extremely simple. Therefore, in some embodiments, metasurface 330 comprises just one single layer. However, two metasurface layers can also be used to extend the operation of the triple-band leaky-wave antenna to more multiband variants. Hence, in some embodiments, the metasurface 330 comprises two layers.

[0043] The disclosed leaky-wave antenna 310 can be used in fixed triple-band systems, as well as for applications with limited scanning (such as few degrees) if used with a phased antenna array, whilst still preserving the high gain and attenuation of grating lobes (with respect to the reference benchmark antenna structure).

[0044] The disclosed leaky-wave antenna 310 can be provided as a stand-alone component or be collocated with, integrated with, or provided in some other type of communication equipment. For example, as disclosed above, with reference to Fig. 3, the triple-band leaky-wave antenna 310 can be part of a transceiver device 300. There can be different examples of such transceiver devices 300, such as (radio) access network nodes, radio base stations, base transceiver stations; node Bs, evolved node Bs, gNBs, access points, transmitter and receiver points, integrated access and backhaul nodes, portable wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, user equipment, smartphones, laptop computers, tablet computers, network-equipped vehicles, etc. to just name a few. Processing circuitry can be provided in the transceiver device 300 using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium. The processing circuitry may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). Particularly, the processing circuitry is configured to cause the transceiver device 300 to perform operations, or actions. For example, the storage medium may store the set of operations, and the processing circuitry may be configured to retrieve the set of operations from the storage medium to cause the transceiver device 300 to perform the set of operations or actions. The set of operations maybe provided as a set of executable instructions. Thus the processing circuitry is thereby arranged to execute methods as herein disclosed. The storage medium may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The transceiver device 300 may further comprise a communications (comm.) interface at least configured for communications with other entities, functions, nodes, and device. As such the communications interface may comprise one or more transmitters and receivers, comprising analogue and digital components. In particularly, the communications interface comprises a triple-band leaky-wave antenna 310 as herein disclosed. The processing circuitry controls the general operation of the transceiver device 300 e.g. by sending data and control signals to the communications interface and the storage medium, by receiving data and reports from the communications interface, and by retrieving data and instructions from the storage medium. Other components, as well as the related functionality, of the transceiver device 300 are omitted in order not to obscure the concepts presented herein.

[0045] Some (radio) access network architectures utilize transceiver devices 300 in terms of network nodes (or gNBs) comprising multiple component parts or nodes: a central unit (CU), one or more distributed units (DUs), and one or more radio units (RUs). The protocol layer stack of the network node is divided between the CU, the DUs and the RUs, with one or more lower layers of the stack implemented in the RUs, and one or more higher layers of the stack implemented in the CU and / or DUs. The CU is coupled to the DUs via a fronthaul higher layer split (HLS) network; the CU / DUs are connected to the RUs via a fronthaul lower-layer split (LLS) network. The DU may be combined with the CU in some embodiments, where a combined DU / CU may be referred to as a CU or simply a baseband unit. A communication link for communication of user data messages or packets between the RU and the baseband unit, CU, or DU is referred to as a fronthaul network or interface. Messages or packets may be transmitted from the transceiver device 300 in the downlink (i.e., from the CU to the RU) or received by the transceiver device 300 in the uplink (i.e., from the RU to the CU).

[0046] 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

CLAIMS1. A triple-band leaky-wave antenna (310) for a transceiver device (300), the triple-band leaky-wave antenna (310) comprising: an antenna structure (100, 320) comprising at least one antenna element (120), wherein the antenna structure (100, 320) is configured to operate in three frequencies fl, f2, £3; and a one-layer metasurface (330) facing the at least one antenna element (120) and placed at a distance (h) on top of the antenna structure (100, 320), wherein the metasurface (330) has a frequency-dependent impedance (500) yielding different reflection properties for the three frequencies fl, f2, f3.

2. The triple-band leaky-wave antenna (310) according to claim 1, wherein, according to the reflection properties, the metasurface (330) is configured to amplify a radiated field of the at least one antenna element (120) for exactly two frequencies, fi, f3, of the three frequencies fl, f2, f3.

3. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein, according to the reflection properties, the metasurface (330) is transparent to a radiated field of the at least one antenna element (120) for only a single one frequency, f2, of the three frequencies fi, f2, f3.

4. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein fl < f2 < f3.

5. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein, according to the reflection properties, the frequency-dependent impedance (500) is inductive for frequency fi, the frequency-dependent impedance (500) is infinite, or undefined, for frequency f2, and the frequency-dependent impedance (500) is capacitive for frequency f3.

6. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein the antenna structure (100, 320) comprises only one single antenna element (120).

7. The triple-band leaky-wave antenna (310) according to any of claims 1 to 5, wherein the antenna structure (100, 320) comprises an array of at least three antenna elements (120).

8. The triple-band leaky-wave antenna (310) according to claim 7, wherein each of the antenna elements is configured to operate in a respective one of the three frequencies fl, f2, f3.

9. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein all the three frequencies fl, f2, f3 are contained within a frequency interval extending from 15 GHz to 35 GHz.

10. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein the distance (h) is contained within a distance interval extending from 2 mm to 10 mm, preferably from 4 mm to 8 mm.

11. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein the metasurface (330) comprises just one single layer.

12. The triple-band leaky-wave antenna (310) according to any of claims 1 to 10, wherein the metasurface (330) comprises two layers.

13. The triple-band leaky-wave antenna (310) according to any preceding claim, wherein the triple-band leaky-wave antenna (310) further comprises a radome (340), and wherein the metasurface (330) is embedded in the radome (340).

14. A transceiver device (300), wherein the transceiver device (300) comprises a triple-band leaky-wave antenna (310) according to any of the preceding claims.

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