Patent Description:
In communications networks, it may be challenging to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

One component of wireless communications networks where it may be challenging to obtain good performance and capacity is the antennas. For example, in order to perform beam-forming (such as beam-width and beam-pointing control) of one or multiple antenna beams/lobes towards desired directions for array antennas, the amplitude and relative phase of the individual signals feeding the individual antenna ports needs to be controlled.

Such control may be enabled by generating individual electrical signals from individual digital signals, in which case the required phase shift is performed in the digital domain. This is referred to as digital beam-forming.

Alternatively, the individual electrical signals may be generated from a common analogue signal, which is split to the desired number of individual signals needed, followed by individual phase-shift in the analogue domain. This is referred to as analogue beam-forming.

Another option for analogue beam-forming is to use different forms of signal distribution networks. One commonly used implementation is the use of the so-called Butler matrix. In such implementations the signal splitting and phase-shifting is performed in the Butler matrix. Such an implementation may generally also require some additional signal switches in order to perform the selection of different beam directions.

There are also beam-forming architectures that use combinations of analogue and digital phase-shifting; e.g., using digital phase-shifting to control the beam in azimuth (sideways) and analogue phase-shifting to control the beam in elevation.

As the skilled person understands, the above disclosed means for beamforming have their particular benefits and limitations. In general terms, digital beam-forming may be considered flexible and may support multiple simultaneous beams, but the implementation may be complicated as it requires individual signal conversion between the digital and the analogue domains. Analogue beam-forming maybe advantageous from the perspective that it relies on analogue signal processing, which does not need to involve multiple instances of data converters (digital-to-analog converters and analog-to-digital converters) and/or up/down converters. Analogue beamforming is commonly less complex than digital beam-forming, but to meet the required phase-accuracy might require a delicate and careful design.

Another limitation for analogue beam-forming is that analogue beamforming inherently only supports a single beam. Providing multiple beams may thus require multiple instances of phase-shifters or, for implementations based on using the Butler matrix, ways to connect multiple analogue signals to multiple inputs of the Butler matrix.

Hence, there is still a need for improved distribution networks for antenna arrangements.

<CIT> describes a background art of a phased array antenna system with adjustable electrical tilt. <CIT> describes a phased array antenna system with electrical tilt control incorporates a tilt controller (<NUM>) for splitting an input signal into three intermediate signals, two of which are delayed by variable delays T1 and T2 relative to the third. <CIT> describes a background art of an active antenna arrangement for transmitting pre-coded signals in a communication system, base station, methods and computer programs.

Furthermore, embodiments of the invention are defined by the claims. An object of embodiments herein is to provide an efficient distribution network for antenna arrangements.

According to a first aspect there is presented a signal distribution network for an antenna arrangement with fewer input ports than antenna elements. The signal distribution network comprises at least two signal splitters. The signal distribution network comprises at least two signal combiners. Each signal splitter is configured to receive one input baseband signal from a unique input port and to provide one direct feed signal as input to a unique antenna element, and to provide intermediate signals as input to two of said at least two signal combiners. Each signal combiner is configured to receive two intermediate signals, each intermediate signal being received from a respective signal splitter of the at least two signal splitters, and to provide one combined signal as input to a unique antenna element, wherein the one combined signal is formed by combining the received two intermediate signals. The signal distribution network further comprises one signal adder configured to provide input to one antenna element of the antenna arrangement, where one of the at least two signal splitters is configured to provide a first input to the signal adder, and one of the at least two signal combiners is configured to provide a second input to the signal adder.

Advantageously this provides an efficient distribution network for antenna arrangements.

Advantageously this provides an efficient distribution network for antenna arrangements in terms of implementation, size, complexity, power-consumption, cost, and/or versatility, or at least a compromise considering all these kinds of terms.

Advantageously, this provides an distribution network to be operatively connected between a (digital) transceiver and the array of antenna elements with a reduced number of transceiver ports compared to the number of antenna elements or antenna element ports.

This is advantageous as the distribution network takes advantage of analogue splitting of one or a few signals, to a higher number of signals while still maintaining the advantages of a digital beam-forming architecture; multiple antenna lobes can be supported and freely placed in a given subspace without restrictions. By digitally controlling the generation of a few signal components and feeding these to the analogue signal distribution network according to the invention, the complexity (e.g., size, weight, power consumption, etc.) of a fully individual digital beam-forming architecture can be avoided.

According to a second aspect there is presented a network node comprising a signal distribution network according to the first aspect.

According to a third aspect there is presented a wireless terminal comprising a signal distribution network according to the first aspect.

According to a fourth aspect there is presented a method for processing signals in a signal distribution network for an antenna arrangement with fewer input ports than antenna elements. The signal distribution network comprises at least two signal splitters, at least two signal combiners, and one signal adder. The method comprises receiving, by each signal splitter, one input baseband signal from a unique input port. The method comprises providing, by each signal splitter, one direct feed signal as input to a unique antenna element, and providing intermediate signals as input to two of said at least two signal combiners. The method comprises receiving, by each signal combiner, two intermediate signals, each intermediate signal being received from a respective signal splitter of the at least two signal splitters. The method comprises providing, by each signal combiner, one combined signal as input to a unique antenna element, wherein the one combined signal is formed by combining the received two intermediate signals. The method comprises providing an input to one antenna element of the antenna arrangement by the signal adder. The method comprises providing, by one of said at least the signal splitters, a first input to the signal adder; and providing, by one of said at least two signal combiners, a second input to the signal adder.

According to a fifth aspect there is presented a computer program for processing signals that, when stored on a computer readable means, can cause the signal distribution network of any of claims <NUM>-<NUM>, to execute method according to claim <NUM>.

It is to be noted that any feature of the first, second, third, fourth, and fifth aspects may be applied to any other aspect, wherever appropriate.

Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, and/or fifth aspect, respectively, and vice versa.

Any method step illustrated by dashed lines should be regarded as optional.

As noted above, an object of embodiments herein is to provide an efficient distribution network for antenna arrangements.

Further, in view of the issues listed above, it may be desirable to provide a distribution network for antenna arrangements that enables the number of digital transmitters to be decreased whilst still having the benefit of being able to generate and control multiple lobes from the same antenna array, that enables generation of relative phase-shift between signal components to multiple antenna elements (or sub-arrays) by a combination of digitally generated signals and an analog distribution/combination network, and/or that supports multiple antenna lobes from the same antenna array and corresponding hardware.

At least some of the embodiments disclosed herein make use of the fact that combining two or more coherent signals by creating vector sums and vector differences can be a way to generate signal components over large antenna arrays. This might be useful when considering that a high number of antenna elements is often needed to generate high antenna gain. At the same time there are requirements on adjustable antenna lobes, ranging from simple vertical tilt to more advanced beam pointing functions. Generating these beam-forming functions in the digital domain may provide more flexibility and capabilities than traditional analogue solutions, for example enabling different frequency carriers in the same frequency band to be controlled individually in order to generate multiple simultaneous beams.

At least some of the embodiments disclosed herein relate to a signal distribution network for an antenna arrangement with fewer input ports than antenna elements. Reference is now made to <FIG> illustrating a signal distribution network 110a for an antenna arrangement 100a according to an embodiment. The signal distribution network 110a comprises at least two signal splitters <NUM> and at least one signal combiner <NUM>.

At each splitter <NUM>, baseband input signals S1, S2,. are split into three equal components (having identical amplitude and phase). <FIG> schematically shows how each of the two three-way splitters <NUM> are configured to serve one output antenna element port E1, E2,. but also two different signal combiners <NUM> each. As will be described in further detail below, particularly with references to <FIG> and <FIG>, at each combiner <NUM> all adjacent baseband input signals are combined in pairs to generate an approximate interpolated new signal vector. Each combiner <NUM> is thus configured to pairwise combine signals from two adjacent splitters <NUM> to create interpolated values of the original input signals S. These interpolated values are fed to output antenna element ports.

The signal distribution network 100a can be described as an infinite ladder of three-way splitters <NUM> and two-to-one combiners <NUM>. There are at least two different options available for truncating this infinite ladder of three-way splitters <NUM> and two-to-one combiners <NUM>. As will be further disclosed below, one option is to omit one of the three outputs from the first and the last signal splitters; another option is to generate a specific difference signal from the first signal combiner and then combining this signal to the unpaired output signal from the three-way combiner (see, for example <FIG> and the description thereof).

The general mechanism to derive signals to additional antenna ports from a smaller set of input ports, as defined by baseband input signals S1, S2,. is to split every input signal in three, where only one of these three identical components are fed directly to the output antenna elements ports E1, E2,. The other two copies of the input baseband signals are combined with the neighboring input baseband signals, which will create new vectors. These vectors can under some conditions be good approximations of intermediate vectors that according to prior art would have been needed at the input side, i.e., where E1 is given by S1, where E2 is given by S2, etc..

Properties of the signal splitters will now be disclosed. Each signal splitter is configured to receive one input baseband signal from a unique input port and to provide one direct feed signal as input to a unique antenna element. Each signal splitter is further configured to provide one intermediate signal as input to at least one of the signal combiner.

Properties of each signal combiner will now be disclosed. Each signal combiner is configured to receive two intermediate signals. Each intermediate signal is received from a respective signal splitter of the at least two signal splitters. Each signal combiner is configured to provide one combined signal as input to a unique antenna element. The combined signal is formed by combining the received two intermediate signals.

Each two-way signal splitter (i.e., a signal splitter having one input and two outputs) may be provided by a Wilkinson <NUM>-way combiner/splitter.

Each three-way signal splitter (i.e., a signal splitter having one input and three outputs) may be provided by a Wilkinson <NUM>-way combiner/splitter.

Each two-way signal combiner (i.e., a signal combiner having two inputs and one output) may be provided by a Wilkinson <NUM>-way combiner/splitter, or a branch-line go-degree hybrid coupler with and added go-degree phase shifter, a rate-race <NUM>-degree hybrid coupler, or a similar type of hybrid coupler.

Further optional properties and features of the signal distribution network will be provided below.

Input signals to the signal distribution network may be regarded as analogue radio frequency (RF) signals, which in turn may be generated from (unique) digital baseband signals. Exactly how the input signals are generated is out of the scope of the present disclosure. One advantage of the proposed signal distribution network is to be able to reduce the digital implementation by introducing small and simple analogue RF components, as defined by the at least two signal splitters and the at least one signal combiner.

Advantageously, by combining some constituting signal components in such a fashion a linear (or at least approximately linear) phase front is generated that in turn will form an antenna beam pointing into a specific direction.

The signal distribution network will mainly be described in a downlink scenario (from the perspective of the radio access network node) where at least one signal is transmitted by antenna ports and thus where signals first are received from the input ports for being processed by the signal distribution network and then fed to the antenna elements. See, for example, the methods disclosed with references to the flowcharts of <FIG>. Hence, in this scenario signals are described as originating from digital baseband representations and further generated as analogue RF signals which are fed into the signal distribution network comprising splitters and combiners, and finally fed to the antenna elements. However, due to reciprocity, it is possible to reverse the signal flow and will then also be applicable for an uplink scenario (from the perspective of the radio access network node). Hence, the signal distribution network is also applicable to a scenario where signals are received by antenna elements and then processed by the signal distribution network before being fed to the input ports. <FIG> schematically illustrates, in terms of a number of functional units, the components of a signal distribution network 110a-110j according to an embodiment. Processing circuitry <NUM> is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product <NUM> (as in <FIG>), e.g. in the form of a storage medium <NUM>.

Particularly, the processing circuitry <NUM> is configured to cause the signal distribution network noa-noj to perform a set of operations, or steps, S100-S112. These operations, or steps, S100-S112 will be disclosed below. For example, the storage medium <NUM> may store the set of operations, and the processing circuitry <NUM> maybe configured to retrieve the set of operations from the storage medium <NUM> to cause the signal distribution network 110a-noj to perform the set of operations.

Thus the processing circuitry <NUM> is thereby arranged to execute methods as herein disclosed. The signal distribution network 110a-110j may further comprise a communications interface <NUM> for communications with other entities and devices, such as an antenna arrangement. As such the communications interface <NUM> may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry <NUM> controls the general operation of the signal distribution network 110a-110j e.g. by sending data and control signals to the communications interface <NUM> and the storage medium <NUM>, by receiving data and reports from the communications interface <NUM>, and by retrieving data and instructions from the storage medium <NUM>.

<FIG> schematically illustrates, in terms of a number of functional modules, the components of a signal distribution network 110a-110j according to an embodiment. The signal distribution network noa-noj of <FIG> comprises a number of functional modules; a receive module 121a configured to perform below steps S102, S106, and a provide module 121b configured to perform below steps S104, S104a, S108. The signal distribution network 110a-110j of <FIG> may further comprises a number of optional functional modules, such as any of a scale module 121c configured to perform below steps S101, S102a, S102b,S108a, an add module 121d configured to perform below step S110, and a split (and phase shift) module 121e configured to perform below steps S100, S112. The functionality of each functional module 121a-121e will be further disclosed below in the context of which the functional modules 121a-121e may be used. In general terms, each functional module 121a-121e may be implemented in hardware or in software. Preferably, one or more or all functional modules 121a-121e may be implemented by the processing circuitry <NUM>, possibly in cooperation with functional units <NUM> and/or <NUM>. The processing circuitry <NUM> may thus be arranged to from the storage medium <NUM> fetch instructions as provided by a functional module 121a-121e and to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

The signal distribution network 110a-110j is provided as a standalone device or as a part of a further device. The signal distribution network 110a-110j is provided in an antenna arrangement 100a-100j. Hence, an antenna arrangement 100a-100j comprise a signal distribution network noa-noj as herein disclosed. The antenna arrangement 100a-100j may be part of a radio access network node (such as a radio base station, a base transceiver station, a nodeB, or an evolved nodeB). The antenna arrangement 100a-100j may additionally or alternatively be part of a wireless devices (such as a mobile station, mobile phone, handset, wireless local loop phone, user equipment (UE), smartphone, laptop computer, tablet computer, or modem).

<FIG> schematically illustrates a network node <NUM> comprising a signal distribution network noa-noj or antenna arrangement 100a-100j comprising such a signal distribution network noa-noj. <FIG> schematically illustrates a wireless device <NUM> comprising a signal distribution network 110a-110j or an antenna arrangement 100a-100j comprising such a signal distribution network 120a-110j. The signal distribution network 110a-110j or the antenna arrangement 100a-100j may be provided as an integral part of the network node <NUM> or the wireless device <NUM>. That is, the components of the signal distribution network 110a-110j or the antenna arrangement 100a-100j may be integrated with other components of the network node <NUM> or wireless device <NUM>; some components of the network node <NUM> or wireless device <NUM> and the signal distribution network 110a-110j or the antenna arrangement 100a-100j may be shared.

<FIG> shows one example of a computer program product <NUM> comprising computer readable means <NUM>. On this computer readable means <NUM>, a computer program <NUM> is stored, which computer program <NUM> cause the processing circuitry <NUM> and thereto operatively coupled entities and devices, such as the communications interface <NUM> and the storage medium <NUM>, to execute methods according to embodiments described herein.

Reference is now made to <FIG> illustrating a method for processing signals in a signal distribution network 110a-110j for an antenna arrangement 100a-100j with fewer input ports than antenna elements as performed by the signal distribution network according to an embodiment. The method is advantageously provided as a computer program <NUM>. As noted above, the signal distribution network 110a-110j comprises at least two signal splitters <NUM> and at least one signal combiner <NUM>.

The signal distribution network is configured to, in a step S102, receive, by each signal splitter, one input baseband signal from a unique input port. The signal distribution network is configured to, in a step S104, provide, by each signal splitter, one direct feed signal as input to a unique antenna element, and to provide one intermediate signal as input to at least one of the at least one signal combiner. The signal distribution network is configured to, in a step S106, receive, by each signal combiner, two intermediate signals, each intermediate signal being received from a respective signal splitter of the at least two signal splitters. The signal distribution network is configured to, in a step S108, providing, by each signal combiner, one combined signal as input to a unique antenna element, wherein the one combined signal is formed by combining the received two intermediate signals.

Reference is now made to <FIG> illustrating methods for processing signals in a signal distribution network for an antenna arrangement with fewer input ports than antenna elements as performed by the signal distribution network according to further embodiments. The method is advantageously provided as a computer program <NUM>.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>) each signal splitter is configured to scale the direct feed signal and the intermediate signal with a first energy conservation factor. The signal distribution network may thus be configured to, in a step S102a, scale, by each signal splitter, the direct feed signal and the intermediate signal with a first energy conservation factor.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>,) each signal splitter is configured to scale the direct feed signal with one first energy conservation factor and the intermediate signal with another first energy conservation factor. The signal distribution network may thus be configured to, in a step S102b, by each signal splitter, scale the direct feed signal with one first energy conservation factor and the intermediate signal with another first energy conservation factor.

According to some embodiments (e.g., any of the embodiments of <FIG>) each signal combiner is configured to scale the combined signal with a second energy conservation factor. The signal distribution network may thus be configured to, in a step S108a, scale, by each signal combiner, the combined signal with a second energy conservation factor.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>) each signal combiner is provided as a hybrid coupler having a sum output port and a difference output port. The combined signal may be provided by the sum output port.

According to some embodiments (e.g., any of the embodiments of <FIG>) the signal distribution network comprises at least two signal combiners. Each signal splitter is configured to provide intermediate signals as input to two of said at least two signal combiners. The signal distribution network thus be configured to, in a step S104a, provide, by each signal splitter, intermediate signals as input to two of said at least two signal combiners.

Special care should be taken when treating the outermost signal splitters. By utilizing the fact that the signal combiner can be provided as a go-degree or <NUM>-degree hybrid coupler, use can be made of not only the sum of the input signals, but also the difference between them. Two ways to realize this is either by using a so-called rat-race combiner or a go-degree hybrid coupler (e.g. a branch-line hybrid) with additional phase-shifts added. By using the difference port of the <NUM>-degree coupler the additional signal components to the outermost antenna elements (which lies outside the elements driven directly by the input signals S1 and S3 in <FIG>) can now be estimated. As seen graphically in <FIG> the input signal components S1 and S2 are first combined as (a scaled version of) S1 - S2 and added to S2 to generate the element component E1. Particularly, according to some embodiments (e.g., the embodiments of <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>) the signal distribution network further comprises a signal adder <NUM>. The signal adder <NUM> may be regarded as a signal combiner where the output is its sigma (or sum) port (Σout), see <FIG>. The signal adder is configured to provide input to one antenna element of the antenna arrangement. One of the at least two combiners is configured to provide a first input to the signal adder. One of the at least one combiner is configured to provide a second input to the signal adder. The signal distribution network may thus be configured to, in a step Sno, add, by the signal adder, a first input and a second input, According to this embodiment each signal combiner may be provided as a hybrid coupler having a sum output port and a difference output port, and the second input may be provided by the difference output port of said one of the at least one combiner.

According to some embodiments (e.g., the embodiment of <FIG>) the signal distribution network further comprises an amplitude tapering unit <NUM>. The amplitude tapering unit is configured to scale one input baseband signal and to provide the scaled one input baseband signal to one of the at least two signal splitters. The signal distribution network may thus be configured to, in a step S101, scale, by a amplitude tapering units114, one input baseband signal and to provide the scaled one input baseband signal to one of the at least two signal splitters.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>, <FIG>) the signal distribution network further comprises a further signal splitter <NUM>. The further signal splitter is configured to split the input to one of the antenna elements into two inputs, and to feed the two inputs to unique antenna elements. The signal distribution network may thus be configured to, in a step S112, by a further signal splitter <NUM>, split the input to one of the antenna elements into two inputs, and to feed the two inputs to unique antenna elements.

According to some embodiments (e.g., any of the embodiments of <FIG>) there is a linear phase increment between the input baseband signals to adjacent ones of the at least two signal splitters. For example, assume that input baseband signal number i can be written as Si=Ai*exp(jϕi), where A is an amplitude factor, j denotes the imaginary unit, ϕ is an angular offset, and exp denotes the exponential function. Then, for i=<NUM>. K-<NUM>, where K is the total number of input baseband signals, there is a phase increment between adjacent phase values of ϕi.

According to some embodiments (e.g., the embodiment of <FIG>) all input baseband signals come from a common input baseband signal provided by a single transmitter chain <NUM>. The common input baseband signal is split and phase shifted by a unit <NUM> to define the input baseband signals before the input baseband signals are fed to the at least two signal splitters. The signal distribution network may thus be configured to, in a step S100, by a unit <NUM>, split and phase shift the input baseband signals to define the input baseband signals.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>) each input baseband signal has its own individual transmitter chain <NUM>.

According to some embodiments (e.g., the embodiment of <FIG>) the signal distribution network is configured to receive N input baseband signals and to provide inputs to 2N-<NUM> antenna elements.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>) the signal distribution network is configured to receive N input baseband signals and to provide inputs to 2N antenna elements.

According to some embodiments (e.g., the embodiment of <FIG>, <FIG>, <FIG>, <FIG>) the signal distribution network is configured to receive N input baseband signals and to provide inputs to 2N+<NUM> antenna elements.

Particular embodiments of signal distribution networks for an antenna arrangement with fewer input ports than antenna elements will now be disclosed with references to <FIG>.

The embodiment of <FIG> represents a realization of a signal distribution network 110a in an antenna arrangement 100a where two signal splitters, one of which is identified at reference numeral <NUM> and three signal combiners, one of which is identified at reference numeral <NUM> are shown.

The embodiment of <FIG> represents a realization of a signal distribution network 110b in an antenna arrangement 100b with five inputs, as defined by baseband signals S1-S5 and nine antenna ports, as defined by antenna elements E2-E10, and where the signal distribution network 110b comprises five signal splitters <NUM> and four signal combiners <NUM>.

<FIG> schematically illustrates a signal components analysis for the combination mechanisms from signals S1-S3 to signals E2 to E4.

The embodiment of <FIG> represents a realization of a signal distribution network 110c in an antenna arrangement 100c with three inputs, as defined by baseband signals S1-S3 and six antenna ports, as defined by antenna elements E1-E6, and where the signal distribution network 110c comprises three signal splitters <NUM>, two signal combiners <NUM>, and one adder <NUM>. The adder is configured to receive one signal contribution a signal splitter and one signal contribution from a signal combiner. The output from the adder defines the signal contribution to antenna element E1. As seen in more detail in <FIG>, the signal combiner from which the adder <NUM> receives one signal contribution generates this signal contribution from its delta (or difference) port (Δout). As seen in more detail in <FIG>, the signal adder <NUM> may be regarded as a signal combiner where the output is its sigma (or sum) port (Σout). Hence, each signal adder <NUM> as disclosed herein may be implemented by a signal combiner.

<FIG> schematically illustrates a signal components analysis for the combination mechanisms from signals S1-S3 to signals E1 to E4.

The embodiment of <FIG> represents a realization of a signal distribution network 110d in an antenna arrangement 100d having three inputs, as defined by baseband signals S1-S3 and fourteen antenna ports, as defined by antenna elements E1-E14, and where each input baseband signal has its own individual transmitter chain, one of which is identified at reference numeral <NUM>. Each transmitter chain has its own transmitter (TRX). The input baseband signals originate from a baseband block <NUM>. The signal distribution network 110d comprises three signal splitters <NUM>, two signal combiners <NUM>, and two signal adders <NUM>. The signal distribution network nod further comprises seven further signal splitters, one of which is identified by reference numeral <NUM>.

The embodiment of <FIG> represents a realization of a signal distribution network 110e in an antenna arrangement 100e similar to the signal distribution network 110d of <FIG> but without further signal splitters and where the signal splitters <NUM> comprises amplitude tapering units <NUM> configured to scale one input baseband signal such that the individual outputs of one signal splitter have different amplitudes.

The embodiment of <FIG> represents a realization of a signal distribution network 110f in an antenna arrangement 100f having four inputs, as defined by baseband signals S1-S4 and eight antenna ports, as defined by antenna elements E1-E8. The signal distribution network 110f comprises four signal splitters <NUM>, two signal combiners <NUM>, and two signal adders <NUM>. In terms of the signal splitters <NUM>, the middle-most signal splitters have two outputs and the outer-most signal splitters have three outputs. Signal values at different stages of the signal distribution network 110f are also indicated. For example, E4=S2/√<NUM>.

The embodiment of <FIG> represents a realization of a signal distribution network <NUM> in an antenna arrangement <NUM> having two inputs, as defined by baseband signals S1-S2 and five antenna ports, as defined by antenna elements E1-E5. The signal distribution network <NUM> comprises two signal splitters <NUM>, one signal combiner <NUM>, two signal adders <NUM>, and one further signal splitter <NUM>. Signal values at different stages of the signal distribution network <NUM> are also indicated.

The embodiment of <FIG> represents a realization of a signal distribution network <NUM> in an antenna arrangement <NUM> having four inputs, as defined by baseband signals S1-S4 and eleven antenna ports, as defined by antenna elements E1-E11. The signal distribution network <NUM> comprises four signal splitters <NUM>, two signal combiners <NUM>, four signal adders <NUM>, and four further signal splitters <NUM>. In terms of the signal splitters <NUM>, the two middle most signal splitters comprises amplitude tapering units (not shown in the figure) configured to scale one input baseband signal such that the individual outputs of one signal splitter have different amplitudes. Signal values at different stages of the signal distribution network <NUM> are also indicated.

The embodiment of <FIG> represents a realization of a signal distribution network 110j in an antenna arrangement 100j having three inputs, as defined by baseband signals S1-S3 and seven antenna ports, as defined by antenna elements E1-E7. All input baseband signals S1-S3 come from a common input baseband signal provided by a single transmitter chain <NUM>. The common input baseband signal is split and phase shifted by a unit <NUM> to define the input baseband signals before the input baseband signals S1-S3 are fed to the three signal splitters <NUM>. The input baseband signals originate from a baseband block <NUM> and share a common transmitter (TRX) along the single transmitter chain <NUM>.

<NUM>(a) and <NUM>(b) schematically illustrate amplitude (in dB) and phase (in degrees) as a function of element index for an antenna arrangement comprising a signal distribution network. The antenna arrangement comprises seven antenna elements and three input baseband signals. <NUM>(a) and <NUM>(b) each element index corresponds to one of the antenna elements. The signal distribution network is defined according to <FIG> where the input baseband signal S1, S2, and S3 additionally have been amplitude tapered as <NUM>, <NUM>, and <NUM>, respectively, and where the element indices in Figs. <NUM>(a) and <NUM>(b) corresponds to the odd numbered antenna elements in <FIG>, i.e., E1, E3, E5,. <NUM>(a) and <NUM>(b) represents four test cases, namely where the phase increments between S1, S2, and S3 is <NUM>, <NUM>, <NUM>, and <NUM> degrees, respectively. These amplitude and phase conditions will in turn generate the seven antenna element signals which will have another amplitude and phase distribution, as illustrated in Figs. <NUM>(a) and <NUM>(b).

<FIG> schematically illustrates, in terms of antenna lobes as response to the stimuli used to obtain the simulation results in Figs. <NUM>(a) and <NUM> (b), a comparison between an antenna arrangement using the signal distribution network as in Figs. <NUM>(a) and <NUM>(b) and a reference antenna arrangement using a one-to-one mapping between input baseband signals and antenna elements, i.e., where Ei = Si, for i=<NUM>, <NUM>,.

<FIG> schematically illustrates schematically illustrates, in terms of antenna lobes in sin(x) representation, where x represents the angle, as response to the stimuli used to obtain the simulation results in Figs. <NUM>(a) and <NUM> (b), a comparison between an antenna arrangement using the signal distribution network as in Figs. <NUM>(a) and <NUM>(b) and the same reference antenna arrangement as in <FIG>.

Table <NUM> summarizes the simulation results in <FIG>, <FIG>, and <FIG>.

Claim 1:
A signal distribution network (noa-noj) for an antenna arrangement (100a-100j) with fewer input ports than antenna elements, comprising:
at least two signal splitters (<NUM>); and
at least two signal combiners (<NUM>),
wherein each signal splitter (<NUM>) is configured to receive one input baseband signal (S1-S4) from a unique input port and to provide one direct feed signal as input to a unique antenna element (E1-E14), and to provide intermediate signals as input to two of said at least two signal combiners (<NUM>);
wherein each signal combiner (<NUM>) is configured to receive two intermediate signals, each intermediate signal being received from a respective signal splitter (<NUM>) of said at least two signal splitters (<NUM>), and to provide one combined signal as input to a unique antenna element (E1-E14), wherein said one combined signal is formed by combining the received two intermediate signals; wherein the signal distribution network (noa-noj) further comprising one signal adder (<NUM>) configured to provide input to one antenna element of the antenna arrangement (100a-100j),
wherein one of said at least two signal splitters (<NUM>) is configured to provide a first input to said signal adder (<NUM>), and wherein one of said at least two signal combiners (<NUM>) is configured to provide a second input to said signal adder (<NUM>).