Apparatus

Abstract

The present invention relates to a beamforming system comprising at least one symmetric weight block, SWB, the SWB arranged to perform as a four-port beamforming network with two input ports and two output ports, the SWB comprising: at least one primary stage 180° hybrid coupler; a 90° fixed phase shifter; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability; and, at least one final stage 180° hybrid coupler.

Description

[0001] APPARATUS Technical Array antennas find application in communications, remote sensing (e.g. real and synthetic RF instruments such as radars, radiometers, altimeters, bi-static reflectometry and radio occultation receivers for signals-of-opportunity missions, etc.), electronic surveillance and defence systems (e.g. air traffic management and generally moving target indicator radars, electronic support measure and jamming systems for electronic warfare, RF instruments for interference analysis and geo-location, etc.), science (e.g. multibeam radio telescopes), satellite navigation systems (where multibeam antennas can be employed in the user and control segments and could, as well, extend space segment capabilities) [1]. In satellite communication systems, Direct Radiating Arrays (DRA) antennas are required to generate multiple spots in a cellular-like configuration, especially for point-to- point services making available higher gains and thus relaxing user terminals requirements. A Beam-Forming Network (BFN) plays an essential role in DRAs antenna architectures [2]. More specifically, it performs the functions of: - in an emitting antenna array, focusing the energy radiated by an array along one or more predetermined directions in space by opportunely phasing and weighting the signals feeding the radiating elements of the array; - in a receiving antenna array, synthesizing one or more receiving lobes having predetermined directions in space by opportunely phasing and weighting the signals received by the antenna elements of the array; and, - in a receiving antenna array, synthesizing one or more nulls in the antenna pattern in the directions of interferers. In a fully reconfigurable configuration, an analogue BFN driving ^ antenna elements for generating ^ independent beams would require ^ ⋅ ^ control nodes. Each control node is typically constituted either by an amplitude and phase control elements or by a vector modulator which includes two amplitude control elements. The complexity of such a network would make it impractical for many applications: simpler solutions retaining sufficient (although not complete) flexibility are therefore necessary. Teshirogi US4584581 [3] describes an Intermediate Frequency (IF) analog multibeam BFN for an array antenna involving symmetry in the arrangement of antenna elements and / or the arrangement of beams, which allows reduction in the number of coupling resistors making up the resistive matrix and consequently in the size and weight of the network. This BFN is based on the use of an analog resistive matrix. The operating principle is based on the distribution of the beam and / or element signals in four different variants, each corresponding to a phase shifted version of the initial signal by 0°, 90°, 180° and 270° respectively. This introduces inefficiency on the signal distribution and renders impossible reconfigurability of the weights, as it would require freedom of selection of the signal to be attenuated from different distribution lines. Exploitation of symmetry in the arrangement of antenna elements and / or the arrangement of beams array was extended in Angeletti and Lisi US9876546 [4] to arrays using digital beamforming networks. Said patent disclosed a digital beam-forming network architecture having a reduced complexity compared to a “fully populated” digital beam-forming network, while being scalable and capable of supporting various array geometries and beam configurations. The complexity reduction was achieved by exploiting different types of symmetries in the element locations and beam pointing directions for reducing the complexity of a “fully populated” digital BFN. While this architecture shows remarkable complexity savings, it remains applicable only to digital beamforming technologies and it does not allow derivation of an analog equivalent configuration. Considering that efficient, modular and scalable antenna architectures can provide a major competitive advantage in terms of hardware reduction (mass, power and cost), reduced non-recurrent costs, and shortened development time (due to the building- blocks approach and to the reusability of developed components), the availability of modular analog BFNs with reduced complexity would allow major improvements.

[0002] of Invention The present invention relates to the reduction of the complexity of analog beamforming networks for direct radiating arrays or arrays magnified by optical means (e.g. reflectors or lenses) exhibiting a form of symmetry between the radiating elements and / or the beam pointing directions (or beam shapes). The disclosed concepts include: • a reconfigurable beamforming architecture, which exploits array symmetry, • a MMIC configuration for implementing it, • an array antenna implementing such beamforming network. The basic building block is a generalization of an IQ Vector Modulator (which is typically composed by two Variable Gain Amplifiers – VGAs) which contemporarily addresses two radially symmetric radiating elements. This is a unit that provides great flexibility during construction and provides significant improvements in terms of chip area and power consumption. The basic 4-nodes (2ൈbeams-2ൈelements) cell is composed by a cascade of 180° hybrid, a 90° fixed phase shifter, two Variable Gain Amplifiers (VGAs) (or variable attenuators) with phase reversing sign capability, a last 180° hybrid. Several other configurations can be derived replacing mentioned elements or cascade of them with functionally equivalent elements. The phase reversing sign capability offers flexibility in changing the sign of the signal. The capability corresponds to a switchable 0° or 180° phase shifter. An advantage is that 2 VGAs are now enough to address 2 radiating elements (which previously required 4 VGAs). The relative saving is of around 50% in both chip area and BFN power consumption. This disclosure therefore provides significant savings in both aspects. The concept can be further extended to symmetric elements and beams with a saving of 75%. • A MMIC configuration implementing the basic building block alone or in a multimode configuration which provides increased integration. • Several array configurations which are based on symmetric sub-arrays which can exploit the symmetric beamforming chip while spatially limiting the interconnection complexity. The array configurations of the disclosure herein include both single beam phased arrays, single beam broadband arrays, and multi-beam arrays both based on hybrid and hierarchical beamforming which can be based on a combination of the proposed analogue configuration and on successive analogue or digital beamforming, or a combination of both. The configurations that may benefit from the present disclosure are many and varied. A possible drawback arising from the need to interconnect radially symmetric elements (that may be largely spaced) to a centralized analogue BFN, is overcome by the hybrid and / or hierarchical array configurations that are also disclosed herebelow. The presented solution is relevant to all applications that need an efficient array including, for example: • Telecom LEO / MEO / GEO multibeam satellite antennas; • Telecom LEO / MEO / GEO user and gateway antennas; • Remote-Sensing RF instruments and RADARs; and, • Wireless base-stations (e.g. xG). In accordance with some embodiments described herein, there is provided a beamforming system comprising at least one symmetric weight block, SWB, the SWB arranged to perform as a four-port beamforming network with two input ports and two output ports, the SWB comprising: at least one primary stage 180° hybrid coupler; a 90° fixed phase shifter; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability; at least one final stage 180° hybrid coupler. A beamforming system may be the SWB alone or the SWN when used in a larger system or the like as would be used in practice. In examples, the SWB is arranged to interconnect couples of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with couples of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis. In examples, the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA). In examples, at least one primary stage 180° hybrid coupler is arranged to receive input signals and provide output signals to the plurality of amplitude control elements. In examples, the 90° fixed phase shifter is arranged between at least one primary stage 180° hybrid coupler and at least one amplitude control element. In examples, the 90° fixed phase shifter is arranged between at least one primary stage 180° hybrid coupler and at least one final stage 180° hybrid coupler. In examples, the at least one final stage 180° hybrid coupler is arranged to receive output signals from a plurality of amplitude control elements. In examples, the system comprises a plurality of SWBs wherein each SWB is independently controllable. In examples, each SWB is arranged to output two signals wherein: the first signal comprises predetermined amplitude and phase weighted single or multi-beam inputs; and, the second signal comprises a respective complex conjugate counterpart. In examples, the amplitude control elements are implemented as at least one of: a four- quadrant VGA; an attenuator; and a one-quadrant VGA amplifier with phase reversing function. In accordance with some embodiments described herein, there is provided a beamforming arrangement comprising at least one symmetric weight block, SWB, the SWB comprising: a first signal input and a second signal input, wherein the first signal input and second signal input are separate, a first 180° hybrid coupler arranged to receive both the first signal input and the second signal input, and arranged to output a first signal output and a second signal output, a 90° phase shifter arranged to receive a signal output from the first 180° hybrid coupler and arranged to output a phase shifted signal output; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability, a first amplitude control element arranged to receive the first signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted first signal output, and a second amplitude control element arranged to receive a signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted second signal output, a second 180° hybrid coupler arranged to receive the amplitude and sign adjusted first signal output from the first amplitude control element and the signal output from the 90° phase shifter and the second amplitude control element. In examples, the arrangement is arranged to interconnect with pairs of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with pairs of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis. In examples, the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA). In examples, the arrangement comprises multiple SWB in a Symmetric Beamforming Network (SYM-BFN) wherein: the signal outputs are split after the first outputs of first 180° hybrid couplers and after the phase shifted second signal outputs from the 90° phase shifters, output signals from homologue amplitude control element with phase reversing sign capability are combined before the first and second inputs of second 180° hybrid couplers. In examples, the signals of the first and second inputs of first 180° hybrid coupler correspond to beams pointing toward directions that are symmetrical with respect to a symmetry axis, and first and second outputs of second 180° hybrid coupler correspond to antenna elements that are arranged symmetrically with respect to said symmetry axis. In examples, the arrangement comprises a first plurality of Symmetric Beamforming Networks (SYM-BFNs), arranged so that each Symmetric Beamforming Network (SYM- BFN) of the first plurality of Symmetric Beamforming Networks (SYM-BFNs) is interconnected to a subset of elements of the array (sub-array), with the elements of each sub-array which are symmetrical with respect to a symmetry axis. In this way, an arrangement may comprise a series of networks while a system may only be a singular network or the like. In examples, the arrangement comprises a second Symmetric Beamforming Network (SYM-BFN) which is interconnected to the first set of Symmetric Beamforming Networks (SYM-BFNs) with the centre of the sub-arrays being symmetrical with respect to a symmetry axis. In examples, the arrangement comprises a plurality of time delay elements, arranged so that the time delay elements provide a controllable time delay to signals to and / or from the first plurality of Symmetric Beamforming Networks (SYM-BFNs). In examples, the plurality of Symmetric Beamforming Networks (SYM-BFNs) are arranged in subunits in a hierarchal arrangement.

[0003] Brief of the Additional features and advantages of the present invention will become apparent from the subsequent description, taken in conjunction with the accompanying drawings, wherein: - Figure 1 illustrates the general geometry of a planar array antenna; - Figure 2 illustrates the pointing direction of a beam generated by a planar array antenna; - Figures 3A-H show different examples of planar array or sub-array geometries to which the present invention can be applied; - Figure 4 illustrates the geometry associated to two axis-symmetric antenna elements pointing at two axis-symmetric directions; - Figure 5 represents a projection of the geometry of Figure 4 along the plane including the axis of symmetry and the pointing vectors; - Figure 6 represents a functional block diagram of a reconfigurable BFN, showing maximal degrees of freedoms; - Figure 7 represents the block diagram of a generic Complex Weighting Element (CWE) used in the BFN of Figure 6; - Figure 8A discloses a Symmetric Weight Block with a Bi-directional implementation based on passive digitally controllable elements; - Figure 8B discloses a Symmetric Weight Block with One-directional implementation based on active digitally controllable elements; - Figure 9 shows the complex conjugate output signals of a Symmetric Weight Block for four different settings of the phase-reversing sign element and different settings of the variable gain block; - Figures 10A-B illustrate the output signals factors for different input ports (Figure 10A for first input port, and Figure 10B for second input port); - Figures 11A-B represent an 8-ports SWB integrating the functionalities of 4 combined 4-ports SWBs, and resulting transfer matrix, respectively; - Figure 11C discloses implementation of an 8-port multimode extension integrating the functionalities of four 4-port elementary Symmetric Weight Blocks with one-directional and bi-directional options based on active digitally controllable elements; - Figure 12 illustrates an 8-ports SWB with a matrix layout which may be more convenient depending on the selected technology implementation; - Figures 13A-B illustrate different matrix layout for increasing the number of SWBs integrated within the same chip; - Figures 14 show a prior-art narrow-band array where the array is composed by sub-arrays that are combined hierarchically combined together; - Figure 15 illustrates an array layout according to an embodiment of the invention where the sub-arrays exhibit local central-symmetry and the phase centres of the sub- arrays exhibit central-symmetry; - Figures 16 show a prior-art broad-band array where the array is composed by sub-arrays. In such array phase-shifters are used at sub-array level and true-time-delay is used to combine different sub-arrays; - Figure 17 illustrates an array layout according to a further embodiment of the invention where the sub-arrays exhibit local central-symmetry and SWB are used at sub- array level, while true-time-delay is used to combine different sub-arrays;. - Figures 18 is a schematic drawing of a prior-art reconfigurable multi-beam antenna system based on sub-arrays; - Figures 19 is a schematic drawing showing a reconfigurable multi-beam antenna system according to an embodiment of the present invention. Sub-arrays exhibit local central-symmetry and SWBs, each with a single-beam port, are used at sub-array level; and, - Figures 20 is a schematic drawing showing a reconfigurable multi-beam antenna system according to a further embodiment of the present invention. Sub-arrays exhibit local central-symmetry and SWBs, each with multi-beam ports, are used at sub-array level. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein. The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

[0004] Detailed An invention described herein relates to an analog beam-forming network (BFN) having a reduced complexity and array antenna comprising the same. Following the notation reported in Angeletti and Lisi US9876546 [4], an array antenna (AA) is composed of a set of ^ radiating elements (RE) placed in the positions ^^and excited by complex weights ^^^^. The array factor ^^^^, ^^ can be evaluated by mean of a Fourier transform of the array discrete field ^^^^, where, ^^^^is the Dirac delta function and, in the case of a planar array (radiating elements disposed in the x-y plane): ^ ൌ ^ ^^^^ ^^ ^^^ ^3^ ^^ ൌ^ ^^ ^ ^^^ ^ ^^^1 െ ^ଶെ ^ଶ^6^Considering that the array is planar and that the antenna elements lie in the x-y plane, it is sufficient to consider for the scalar product ^^⋅ of the steering vector ^^on the x-y plane. ^^ൌ ^^sin^ϑ^cos^φ^ ^ ^^sin^ϑ^sin^φ^ ൌ ^^^^^^ ^ ^^^^ ^7^ The indexes of theௌ^radiating elements fulfilling a symmetry condition can be re- numbered and grouped in ordered couples ^^, െ^^ such that a spatial transformation ^^.^of the element ^^ would result in the element ^ି^:^^^^^ൌ ^ି^ ൌ െ^^ ^8^In particular, the array of Figure 1 is axis-symmetric, with a symmetry axis coinciding with the z Cartesian axis. It is worth noting that the class of planar arrays with axis-symmetric radiating elements is quite vast and include a large number of array geometries. Specific examples are reported in Figure 3A to Figure 3H, where dots represents radiating elements.With the introduced renumbering and considering the projection ^^ of steering vector ^^on the x-y plane, equation (2) can be rearranged as, The coordinates system and the radiation pattern coordinates system are briefly described in Figure 1, Figure 2, respectively. One of the most advantageous features of array antennas is the simplicity of performing beam scanning. Defining a prototypal beam with an excitation set ^^^^^ and an array factor, pointed to the broadside direction ^^^ ≡^^^, ^^^ൌ^0,0^, to scan the beam AB to thedirection ≡^^, ^^(see Figure 2), the new set of excitations, ^^^, ^^^, can be derivedfrom the as, ^^^, ^^^ൌ ^^^^^exp^െ^^^^^ ⋅ ^^^ൌ ^^^^^s^^^, ^^^^11^where the steering factor s^^^, ^^^represents the phase correction required to align the array phase-front with respect to the pointing direction, as defined by the following equation: s^^^, ^^^ ൌ exp^െ^^^^^⋅ ^^^ ^12^As shown on Figure 2, ^ and ^ define the direction of the unity steering vector ^^, i.e. they carry information equivalent to the angles ^ and ^ formed by the beam pointing direction and the z axis and the x axis, respectively. Equation (11) shows the possibility of separating excitation tapering for beam shape and sidelobes control from phase steering for beam pointing. From Equation (12) it is possible to derive the steering factor necessary for an axis- symmetric element, ^ି^ൌ െ^^^13^s^^ି^, ^^^ ൌ exp^െ^^^^^⋅ ^ି^^ ൌ exp^^^^^^⋅ ^^^ ^14^ which can be summarised as, s^^ି^, ^^^ൌ s∗^^^, ^^^^15^where “∗”represents complex conjugation. Relationship Error! Reference source not found. can be better understood by means of Figure 4 and Figure 5 where it is pictorially shown how centre-symmetric elements require for the steering factor, an identical electrical length but opposite signs. Similarly it can be appreciated that to generate a beam pointing in the opposite centre- symmetric direction െ^^, the steering factor of the n-th elements would need a conjugate steering factor, such that the following hold true: s^^^, െ^^^ൌ s∗^^^, ^^^^16^Also this relationship can be understood examining Figure 4 and Figure 5, where it is pictorially shown how the centre-symmetric steering direction െ^^would require an electrical length equivalent to the one relevant to the steering ^^but with an opposite sign. Lastly, it can also be demonstrated that to generate a beam pointing in the opposite centre-symmetric direction െ^^, the steering factor for the -n-th axis-symmetric element (i.e. the element axially-symmetric with respect to the n-th element) would need a conjugate steering factor: s^^ି^, െ^^^ൌ s^^^, ^^^^17^The above identities (15), (16), and (17), follow from Equations (12) and (13). In multi-beam antennas the ^ antenna elements are reused for generating ^ independent beams, each pointing at a steering direction ^^^. Indicating with ^ௌthe couples of axial-symmetric beam steering directions, the beamindexes can be grouped in ordered couples^^,െ^^such that^^^^^^ ൌ ^^ି^ൌ െ^^^^18^the complex beam-forming will represent the complex multiplicative factor to apply to the m-th beam to obtain the n-th antenna element (15), (16) and (17) can be summarised in the following equations ^ൌ ^∗ ି^,^ ^,^^^,ି^ൌ ^^∗,^^20^^ି^,ି^ൌ ^^,^^21^The functional block diagram of a fully populated BFN is reported in Figure 6 showing maximal degrees of freedoms but with a high complexity. Previous arrangements may have used this approach. Improvements to this approach are discussed and disclosed herein. This BFN has a set BP of ^ beam ports (BP, input ports), and a set EP of ^ antenna element ports (EP, output ports), and comprises ^ ⋅ ^ complex weighting elements (CWE). The signals entering the BFN through each beam port are distributed to ^ complex weighting elements CWE by signal splitters SP. Each antenna port outputs an excitation signal obtained by adding the output signals of ^ complex weighting elements using signal combiners (SC). The block diagram of a generic Complex Weighting Element (CWE) used in the BFN of Figure 6 is shown in Figure 7 and corresponds to an implementation that is known as Cartesian Vector Modulator. Modern vector modulators are two port devices having one input port and an output port. Each Cartesian vector modulator is composed by two passive variable attenuators or variable gain amplifiers (shown in Figure 7), both with phase-reversing sign capability. The present invention discloses a Symmetric Weight Block (SWB) which can be implemented in monolithic microwave integrated circuit (MMIC) technology for symmetrical beamforming. Multiple identical Symmetric Weight Blocks (SWBs) can be integrated together and individually controlled to operate in parallel. In the elementary configuration, each Symmetric Weight Block (SWB) acts as a four-port beamforming network with two input ports and two output ports. Each Symmetric Weight Block (SWB) is controlled independently and outputs two signals: 1) a first output signal that contains single or multi-beam inputs amplitude and phase weighted according to required beam-steering direction needs and 2) a second output signal that contains its complex conjugate counterpart. Depending on the configuration of the BFN, the multi-node MMIC allows feeding input signals such that the output conjugate signals are reversed between the two outputs. The Symmetric Weight Block (SWB) of the present invention acts as a combination of 4 phase shifters (or cartesian vector modulators) with capability to continuously steer the amplitude and phase of signal while providing two conjugate outputs that are fed to antenna array elements in symmetrical fashion, hence reducing the BFN complexity to half (if only three of the four ports are used), or to one forth (if all four ports are used) of the conventional arrays with independent array element feeding. Required amplitude and phase resolution is achieved through digital control. The present Symmetric Weight Block (SWB) is implementable in multiple semiconductor processes but given the evolution of silicon technologies over the past decade, SiGe BiCMOS and SOI are the most suitable processes to achieve the highest degree of integration, high-speed, low-noise, path-to-path isolation and digital functionality. A four-port Symmetric Weight Block (SWB) acts as a cartesian vector modulator with conjugate outputs. Key building blocks are 1) input four-port 180° signal splitter, 2) in- phase 90° phase shifter, 3) four-quadrant in-phase and quadrature phase and amplitude adjustable conditioning blocks and 4) output four-port 180° signal combiner. Figure 9 shows the complex conjugate output signals of a Symmetric Weight Block for four different settings of phase reversing 180° phase shifters in the quadrature paths and attenuators are set from 0 to 12 dB with step of 3 dB. Polar plot shown in clockwise order for 180° phase shifters configured as follows: [0°, 0°]; [180°, 180°]; [180°, 0°]; [0°, 180°]. Input and output 180° combiners can be implemented as passive symmetrical four ports, such as 180°hybrid couplers, relying on transmission lines, on-chip inductors, capacitors and transformers. The 90° phase shifter can be implemented using compact on-chip lumped elements. Alternatively, the first two blocks, i.e. 180° combiner and 90° phase shifter can be implemented as a single circuit in a form of symmetrical polyphase network or an active phase shifter to assure layout symmetry in both I and Q paths. In-phase and quadrature amplitude control can be implemented either using passive switchable attenuators (e.g. balanced reflect type vector modulator) (as shown in Figure 8A) or active variable gain amplifiers (as shown in Figure 8B) with phase reversing functionality (e.g. Gilbert cell VGA implementation that allows four-quadrant beam-steering operation). The Gilbert cell VGA is one of a number of ways of implementing a gain control block. Other options that provide the same function may be used in the present arrangement. Other options include use of one or more four-quadrant VGAs, attenuators, and one-quadrant VGA amplifier with phase reversing function. As used herein, the term 180° hybrid coupler may be used to refer to more generally a 180° signal splitter. From a functional position, these may provide a desirable outcome for the beamforming network. Depending on the implementation of in-phase and quadrature phase and amplitude adjustable conditioning blocks, the present invention can operate bi-directionally (Figure 8A), allowing the signal to travel in either direction while maintaining the phase and complex conjugate properties at the outputs. The latter is particular interest for implementation of transmit and receive duplexing schemes, allowing single aperture transmission and reception using the identical beamforming MMICs, hence reducing system complexity and costs. An example of the present disclosure may comprise at least one Symmetric Weight Block (SWB) for symmetric elements / symmetric beams interconnecting a first and second antenna ports, to be associated to respective antenna elements which are arranged symmetrically with respect to a symmetry axis, with a first and a second beam ports, corresponding to respective antenna beams pointing toward directions which are symmetrical with respect to a symmetry axis. A basic embodiment of the invention comprises at least one Symmetric Weight Block (SWB) interconnecting couples of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with couples of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis. An example of an SWB is shown in Figure 8A. The achieved complexity reduction is due to either: - Element positions axial-symmetry; - Beam steering direction axial-symmetry; - Combination of element positions axial-symmetry and beam steering direction axial-symmetry. Referring to a standard implementation of a cartesian vector modulator which uses two amplitude control elements (either variable attenuators or variable gain amplifiers) the complexity saving of a 4-port Symmetric Weight Block (SWB) can be quantified in: - 50% for element positions axial-symmetry; - 50% for beam steering direction axial-symmetry; - 75% for combination of element positions axial-symmetry and beam steering direction axial-symmetry. A broader combination of the possible symmetries and non / symmetries exists, i.e.: - Asymmetric-Beams / Asymmetric-Elements; - Asymmetric-Beams / Symmetric-Elements; - Symmetric-Beams / Asymmetric -Elements; - Symmetric -Beams / Symmetric-Elements. The 4-port Symmetric Weight Block (SWB) described above and represented in Figure 8A-B, can be integrated together with others Symmetric Weight Blocks increasing the number of beams and / or the number of elements. Figure 11A represents an 8-ports SWB integrating the functionalities of 4 combined 4- ports SWBs. The resulting 8-ports SWB serves 2 independent beam ports and 2 symmetric beam ports and 2 couples of symmetric radiating elements. The resulting transfer matrix in reported in Figure 11B. In comparison, a conventional multi-node BFN chip serving 4 input beams and 4 output radiating elements would have required 32 variable attenuators or variable gain amplifiers (instead of the 8 of the present arrangement). This is clearly a significant reduction in the number of elements and therefore the cost of the arrangement. Furthermore, with fewer elements within the arrangement, the likelihood of one element breaking and requiring the system to be serviced is reduced. Additionally, increase of the number of input and outputs in the same SWB chip allows for a reduction of the number of required 180° hybrids with respect to a configuration where the SWBs are realised individually and combined externally. Figure 11C discloses implementation of an 8-port multimode extension integrating the functionalities of four 4-port elementary Symmetric Weight Blocks with one-directional and bi-directional options based on active digitally controllable elements. Figure 12 shows an 8-ports SWB with a matrix layout which may be more convenient depending on the selected technology implementation. The number of SWB integrated within the same chip can be further extended as shown in Figure 13A-B. An example of exploitation of the disclosed Symmetric Weight Block (SWB) architecture in array antennas is shown schematically in Figures 15, 17, 19 and 20, whereas other modern architectures are shown in Figures 14, 16 and 18. Figures 14 shows a modern narrow-band array wherein the array is composed by sub- arrays that are hierarchically combined together. Exploiting the local central-symmetry of the elements composing each sub-array, phase steering at sub-array level can be performed by a Symmetric Weight Block (SWB) with element ports corresponding to the sub-array elements. To align the phase fronts achieved at sub-array level a further layer of phase-shifters would be required. In case sub-arrays phase centres exhibit central-symmetry a second layer Symmetric Weight Block (SWB) can be used with element ports of the second layer SWB corresponding sub-arrays. Such an embodiment, an example of the present arrangement, is depicted in Figure 17. It is worth mentioning that the design of the sub-arrays and of the array of sub-array can be optimised taking into consideration the central-symmetry constraints that can allow simplifying the overall antenna architecture. Both the array configurations of Figures 14 and 15 are typically applicable to narrowband scenarios, as they are based on phase shifters. A bandwidth increase can be achieved substituting phase-shifters with true-delay-lines (TDLs) which are more complex to realize if re-configurability is required. Prior-art configurations that achieve broad-band while limiting the number of reconfigurable TDLs are based on hierarchical decomposition of the array in sub-arrays, where phase-shifting is applied at sub-array level and delay is applied between sub-arrays. Such prior-art configuration is shown in Figure 16. An embodiment of the present invention that provides broad-band while reducing the sub-array beamforming complexity is illustrated in Figure 17. In this embodiment sub- arrays exhibit local central-symmetry and SWBs are used at the sub-array level, while true-time-delay is used to combine different sub-arrays. A prior-art reconfigurable multi-beam antenna system based on sub-arrays is reported in Angeletti, Toso, and Petrolati, European Patent Application No. EP18206061 [6], and is shown in Figures 18. The reconfigurable multibeam antenna system of Figure 18 is capable of simultaneously activating one or more beams over a given Variable Field of View (V-FOV). The instantaneous V-FOV is obtained steering the sub-array pattern accordingly. Within said V-FOV, the second-layer Reconfigurable BFN is able to generate a multitude of narrow- beams. The sub-array beamforming complexity is illustrated in Figure 17. In this embodiment sub-arrays exhibit local central-symmetry and SWBs are used at sub-array level, while true-time-delay is used to combine different sub-arrays. According to an embodiment of the present invention illustrated in Figure 19, the complexity of a reconfigurable multibeam antenna can be reduced exploiting sub-arrays with local central-symmetry interconnected to SWBs, each SWB having a single-beam port. The sub-arrays single-beam ports are interconnected to the second-layer Reconfigurable BFN which is able to generate a multitude of narrow-beams. The sub- array SVBs steer each sub-array pattern to the instantaneous V-FOV, while reducing of 50% the sub-array BFN complexity. A further embodiment of the present invention is illustrated in the schematic drawing of Figures 20 which shows an extension of the embodiment of Figure 19 to a reconfigurable multi-beam antenna with multiple Variable Field of View (V-FOV). Within each of said multiple V-FOV, a multitude of second-layer Reconfigurable BFNs are able to generate multiple narrow-beams. In this embodiment sub-arrays with local central-symmetry interconnected to multibeam SWBs, each SWB having a multiple-beam ports. Each SWB beam correspond to a V-FOV. Ports of the multibeam SWBs corresponding to same V- FOV are connected to independent second-layer Reconfigurable BFNs which realize a multitude of narrow-beams within corresponding V-FOV. In both the embodiments of Figures 19 and 20, if the sub-arrays` phase centres exhibit central symmetry, the Reconfigurable BFNs can be realised with reduced complexity by mean of SWBs in a hierarchical fashion. Second-layer Reconfigurable BFNs can also be implemented as reconfigurable analog or digital BFNs. Further examples of feature combinations taught by the present disclosure are set out in the following first set of numbered clauses: FIRST SET OF CLAUSES: 1. A beamforming system comprising at least one symmetric weight block, SWB, the SWB arranged to perform as a four-port beamforming network with two input ports and two output ports, the SWB comprising: at least one primary stage 180° hybrid coupler; a 90° fixed phase shifter; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability; at least one final stage 180° hybrid coupler. 2. A beamforming system according to clause 1, wherein the SWB is arranged to interconnect couples of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with couples of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis. 3. A beamforming system according to clause 1 or 2, wherein the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA). 4. A beamforming system according to any preceding clause, wherein at least one primary stage 180° hybrid coupler is arranged to receive input signals and provide output signals to the plurality of amplitude control elements. 5. A beamforming system according to any preceding clause, wherein the 90° fixed phase shifter is arranged between at least one primary stage 180° hybrid coupler and at least one final stage 180° hybrid coupler. 6. A beamforming system according to any preceding clause, wherein the at least one final stage 180° hybrid coupler is arranged to receive output signals from a plurality of amplitude control elements. 7. A beamforming system according to any preceding clause, comprising a plurality of SWBs wherein each SWB is independently controllable. 8. A beamforming system according to any preceding clause, wherein each SWB is arranged to output two signals wherein: the first signal comprises predetermined amplitude and phase weighted single or multi-beam inputs; and, the second signal comprises a respective complex conjugate counterpart. 9. A beamforming system according to any preceding clause, wherein the amplitude control elements are implemented as at least one of: a four-quadrant VGA; an attenuator; and a one-quadrant VGA amplifier with phase reversing function. 10. A beamforming arrangement comprising at least one symmetric weight block, SWB, the SWB comprising: a first signal input and a second signal input, wherein the first signal input and second signal input are separate, a first 180° hybrid coupler arranged to receive both the first signal input and the second signal input, and arranged to output a first signal output and a second signal output, a 90° phase shifter arranged to receive a signal output from the first 180° hybrid coupler and arranged to output a phase shifted signal output; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability, a first amplitude control element arranged to receive the first signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted first signal output, and a second amplitude control element arranged to receive a signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted second signal output, a second 180° hybrid coupler arranged to receive the amplitude and sign adjusted first signal output from the first amplitude control element and the signal output from the 90° phase shifter and the second amplitude control element. 11. The beamforming arrangement of clause 10, wherein is arranged to interconnect with pairs of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with pairs of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis. 12. A beamforming system according to clause 10 or 11, wherein the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA). 13. The beamforming arrangement of any of clauses 10-12, integrating multiple SWB in a Symmetric Beamforming Network (SYM-BFN) wherein: the signal outputs are split after the first outputs of first 180° hybrid couplers and after the phase shifted second signal outputs from the 90° phase shifters, output signals from homologue amplitude control element with phase reversing sign capability are combined before the first and second inputs of second 180° hybrid couplers. 14. The beamforming arrangement of any of clauses 10 to 13, wherein the signals of the first and second inputs of first 180° hybrid coupler correspond to beams pointing toward directions that are symmetrical with respect to a symmetry axis, and first and second outputs of second 180° hybrid coupler correspond to antenna elements that are arranged symmetrically with respect to said symmetry axis. 15. A symmetric beamforming arrangement according to any of clauses 10-14, comprising a first plurality of Symmetric Beamforming Networks (SYM-BFNs), arranged so that each Symmetric Beamforming Network (SYM-BFN) of the first plurality of Symmetric Beamforming Networks (SYM-BFNs) is interconnected to a subset of elements of the array (sub-array), with the elements of each sub-array which are symmetrical with respect to a symmetry axis. 16. A symmetric beamforming arrangement according to clause 13 or 15, comprising a second Symmetric Beamforming Network (SYM-BFN) which is interconnected to the first set of Symmetric Beamforming Networks (SYM-BFNs) with the centre of the sub- arrays being symmetrical with respect to a symmetry axis. 17. A symmetric beamforming arrangement according to clause 13, 15 or 16, comprising a plurality of time delay elements, arranged so that the time delay elements provide a controllable time delay to signals to and / or from the first plurality of Symmetric Beamforming Networks (SYM-BFNs). 18. The beamforming arrangement according to clause 13, 15, 16 or 17, wherein the plurality of Symmetric Beamforming Networks (SYM-BFNs) are arranged in subunits in a hierarchal arrangement. Further examples of feature combinations taught by the present disclosure are set out in the following second set of numbered clauses: SECOND SET OF CLAUSES: 1. A beamforming system comprising at least one symmetric weight block, SWB, the SWB arranged to perform as a four-port beamforming network with two input ports and two output ports, the SWB comprising: at least one primary stage 180° hybrid coupler; a 90° fixed phase shifter; a plurality of variable gain amplifiers; at least one final stage 180° hybrid coupler. 2. A beamforming system according to clause 1, wherein at least one primary stage 180 hybrid coupler are arranged to receive input signals and provide output signals to the plurality of variable gain amplifiers. 3. A beamforming system according to clause 1 or 2, wherein the 90° fixed phase shifter is arranged between at least one primary stage 180° hybrid coupler and at least one final stage 180° hybrid coupler. 4. A beamforming system according to any preceding clause, wherein the at least one final stage 180° hybrid coupler is arranged to receive output signals from at least one variable gain amplifier. 5. A beamforming system according to any preceding clause, comprising a plurality of SWBs wherein each SWB is independently controllable. 6. A beamforming system according to any preceding clause, wherein each SWB is arranged to output two signals wherein: the first signal comprises predetermined amplitude and phase weighted single or multi-beam inputs; and, the second signal comprises a respective complex conjugate counterpart. 7. A beamforming system according to any preceding clause, wherein at least one variable gain amplifier is within a Gilbert cell VGA. 8. A beamforming arrangement comprising at least one symmetric weight block, SWB, the SWB comprising: a first signal input and a second signal input, wherein the first signal input and second signal input are separate, a first 180° hybrid coupler arranged to receive both the first signal input and the second signal input, and arranged to output a first signal output and a second signal output, a 90° phase shifter arranged to receive the second signal output from the first 180° hybrid coupler and arranged to output a shifted second signal output; a second 180° hybrid coupler arranged to receive the first signal output and the shifted second signal output. 9. The beamforming arrangement of clause 8, further comprising at least one amplifier. 10. The beamforming arrangement of clause 8 or 9, wherein the arrangement is arranged to provide / use symmetric and asymmetric symmetry. 11. The beamforming arrangement of any of clauses 8-10, wherein the first signal output is split before second 180° hybrid coupler. 12. The beamforming arrangement of clause 11, wherein the shifted second signal output is split before second 180° hybrid coupler. 13. The beamforming arrangement of clause 11 or 12, further comprising a further second 180° hybrid coupler arranged to receive a portion of the split first signal output and a portion of the split shifted second signal output. 14. The beamforming arrangement of any of clauses 11-13, comprising four amplifiers: a first amplifier receiving the first portion of the split first signal output a second amplifier receiving the second portion of the split first signal output a third amplifier receiving the first portion of the split shifted second signal output a fourth amplifier receiving the second portion of the split shifted second signal output. 15. The beamforming arrangement of any of clauses 8 to 14, wherein the signal output by the hybrid couplers is symmetric. 16. The beamforming system of clauses 1-7, or the beamforming arrangement of any of clauses 8 to 14, comprising a plurality of SWBs and a plurality of time delay elements, arranged so that the time delay elements provide a controllable time delay to signals to and from the SWBs. 17. The beamforming system or arrangement of clause 16, wherein an output signal is symmetric. 18. The beamforming system or arrangement of clause 16 or 17, wherein the plurality of SWBs are arranged in subunits in a hierarchal arrangement.

[0005] REFERENCES [1] C. Mangenot, G. Toso, P. Angeletti, “Active Arrays for Satellite Applications: the Quest for increased Power Efficiency”, in I. E Lager, M. Simeoni, (Editors), Antennas for Ubiquitous Radio Services in a Wireless Information Society, IOS Press, 2010 [2] P. Angeletti, M. Lisi, “Beam-Forming Network Developments for European Satellite Antennas”, (Special Report), Microwave Journal, Vol.50, No.8, Aug.2007 [3] T. Teshirogi, Beam forming network for multibeam array antenna, US Patent No. US4584581, April 1986 [4] P. Angeletti, M. Lisi, Digital Beam-Forming Network having a Reduced Complexity and Array Antenna Comprising the same, US Patent No. US9876546, January 2018. [5] P. Angeletti, G. Toso, D. Petrolati, A Reconfigurable Multibeam Antenna System, European Patent Application No. EP18206061, (filed on 13 / 11 / 2018, EP3654544A1 published on 20 / 05 / 2020),

Claims

CLAIMS 1. A beamforming system comprising at least one symmetric weight block, SWB, the SWB arranged to perform as a four-port beamforming network with two input ports and two output ports, the SWB comprising: at least one primary stage 180° hybrid coupler; a 90° fixed phase shifter; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability; and, at least one final stage 180° hybrid coupler.

2. A beamforming system according to claim 1, wherein the SWB is arranged to interconnect couples of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with couples of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis.

3. A beamforming system according to claim 1 or 2, wherein the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA).

4. A beamforming system according to any preceding claim, wherein at least one primary stage 180° hybrid coupler is arranged to receive input signals and provide output signals to the plurality of amplitude control elements.

5. A beamforming system according to any preceding claim, wherein the 90° fixed phase shifter is arranged between at least one primary stage 180° hybrid coupler and at least one final stage 180° hybrid coupler.

6. A beamforming system according to any preceding claim, wherein the at least one final stage 180° hybrid coupler is arranged to receive output signals from a plurality of amplitude control elements.

7. A beamforming system according to any preceding claim, comprising a plurality of SWBs wherein each SWB is independently controllable.

8. A beamforming system according to any preceding claim, wherein each SWB is arranged to output two signals wherein: the first signal comprises predetermined amplitude and phase weighted single or multi-beam inputs; and, the second signal comprises a respective complex conjugate counterpart.

9. A beamforming system according to any preceding claim, wherein the amplitude control elements are implemented as at least one of: a four-quadrant VGA; an attenuator; and a one-quadrant VGA amplifier with phase reversing function.

10. A beamforming arrangement comprising at least one symmetric weight block, SWB, the SWB comprising: a first signal input and a second signal input, wherein the first signal input and second signal input are separate, a first 180° hybrid coupler arranged to receive both the first signal input and the second signal input, and arranged to output a first signal output and a second signal output, a 90° phase shifter arranged to receive a signal output from the first 180° hybrid coupler and arranged to output a phase shifted signal output; a plurality of amplitude control elements comprising a phase-sign reversing element arranged to provide phase reversing sign capability, a first amplitude control element arranged to receive the first signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted first signal output, and a second amplitude control element arranged to receive a signal output from the first 180° hybrid coupler and arranged to output an amplitude and sign adjusted second signal output, a second 180° hybrid coupler arranged to receive the amplitude and sign adjusted first signal output from the first amplitude control element and the signal output from the 90° phase shifter and the second amplitude control element.

11. The beamforming arrangement of claim 10, wherein the arrangement is arranged to interconnect with pairs of antenna elements, which are arranged symmetrically with respect to a symmetry axis, with pairs of beam ports, corresponding to beams pointing toward directions which are symmetrical with respect to said symmetry axis.

12. A beamforming arrangement according to claim 10 or 11, wherein the amplitude control elements comprise at least one Variable Gain Amplifier (VGA) and / or at least one Variable Attenuator (VA).

13. The beamforming arrangement of any of claims 10-12, integrating multiple SWB in a Symmetric Beamforming Network (SYM-BFN) wherein: the signal outputs are split after the first outputs of first 180° hybrid couplers and after the phase shifted second signal outputs from the 90° phase shifters, output signals from homologue amplitude control element with phase reversing sign capability are combined before the first and second inputs of second 180° hybrid couplers.

14. The beamforming arrangement of any of claims 10 to 13, wherein the signals of the first and second inputs of first 180° hybrid coupler correspond to beams pointing toward directions that are symmetrical with respect to a symmetry axis, and first and second outputs of second 180° hybrid coupler correspond to antenna elements that are arranged symmetrically with respect to said symmetry axis.

15. A symmetric beamforming arrangement according to any of claims 10-14, comprising a first plurality of Symmetric Beamforming Networks (SYM-BFNs), arranged so that each Symmetric Beamforming Network (SYM-BFN) of the first plurality of Symmetric Beamforming Networks (SYM-BFNs) is interconnected to a subset of elements of the array (sub-array), with the elements of each sub-array which are symmetrical with respect to a symmetry axis.

16. A symmetric beamforming arrangement according to claim 13 or 15, comprising a second Symmetric Beamforming Network (SYM-BFN) which is interconnected to the first set of Symmetric Beamforming Networks (SYM-BFNs) with the centre of the sub- arrays being symmetrical with respect to a symmetry axis.

17. A symmetric beamforming arrangement according to claim 13, 15 or 16, comprising a plurality of time delay elements, arranged so that the time delay elements provide a controllable time delay to signals to and / or from the first plurality of Symmetric Beamforming Networks (SYM-BFNs).

18. The beamforming arrangement according to claim 13, 15, 16 or 17, wherein the plurality of Symmetric Beamforming Networks (SYM-BFNs) are arranged in subunits in a hierarchal arrangement.

Images