Analog beam squint suppression technique

Abstract

A transmitter (300) for transmitting radio frequency, RF, signals via an antenna array (210) and a receiver (400) for receiving RF signals via an antenna array (210). The transmitter (300) comprises N branches for providing respective RF signals to respective antenna elements of the antenna array (210), where N is an integer larger than 1. Each branch of the N branches comprises M mixers (304, 305, 314), where M is an integer larger than 1. In each branch of the N branches, each mixer of the M mixers (304, 305, 314) is configured to receive a respective analog sub-band baseband signal and upconvert said respective analog sub-band baseband signal to a respective sub-band RF signal. In each branch of the N branches, the M mixers (304, 305, 314) are configured to introduce a difference in phase between each of the M sub-band RF signals. The receiver (400) comprises N branches configured to receive respective RF signals from respective antenna elements of the array antenna (210), where N is an integer larger than 1. Each branch of the N branches comprises M mixers (404, 405), where M is an integer larger than 1. Each branch of the N branches comprises a respective splitter (403) configured to split the RF signal received by that branch to the M mixers (404, 405) of that branch. In each branch of the N branches, each mixers of the M mixers (404, 405) is configured to receive the RF signal received by the corresponding branch and downconvert said RF signal to an analog baseband signal. In each branch of the N branches, the M mixers (404, 405) are configured to introduce a difference in phase between each of the analog baseband signals.

Description

[0001] ANALOG BEAM SQUINT SUPPRESSION TECHNIQUE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to the field of wireless communication. More particularly, the present disclosure relates to a transmitter for transmitting radio frequency (RF) signals via an antenna array, a receiver for receiving RF signals via an antenna array, a method for transmitting RF signals via an antenna array, and a method for receiving RF signals via an antenna array.

[0004] BACKGROUND

[0005] Beam steering in an antenna array is achieved by phase shifting the signal to be transmitted or the received signal by a different amount at each antenna element in the antenna array. With equidistant placement of antenna elements in a one-dimensional array, and for constructive interference in an intended beam direction 0 from boresight, follows the equation below d sin d t = - c where t is the time delay of the signal between two neighboring antenna elements, c is the speed of light in vacuum, and d is the distance between two neighboring antenna elements.

[0006] Figure 2 illustrates a transceiver 200 with an antenna array 210 comprising four antenna elements 211 :214. Boresight is illustrated by the dashed line 231. The intended beam direction is illustrated by dashed arrow 232, which is oriented at an angle 0 relative to the boresight.

[0007] Ideally, the time delay t is accomplished using a true time delay (TTD), and signal components over the entire bandwidth of the signal will then have their time shifted equally, which would result in that signal components at all frequencies would fully benefit from the available beamforming gain of the antenna array. The beamforming gain makes it possible increase the signal strength when communicating with a device that is located in the direction of the beam. If the beam points directly at the device the beamforming gain scales linearly with the number of antenna elements in the antenna array. There are different architectures for beamforming transceivers. One main categorization is analog and digital architectures. Digital beamforming is more flexible, for instance being able to form multiple beams and to approximate TTD, but has a higher cost as each antenna element requires a complete signal chain from antenna to digital, i.e., it requires separate analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) for each antenna element in the antenna array. There is also a digital signal processing part that will be large and power consuming for wideband signals and large array sizes. Analog beamforming is less flexible than digital, but requires less hardware and signal processing. It can also provide better immunity to interfering signals outside the beam direction. In large antenna arrays, combinations of analog and digital beamforming can be used to find a good balance between flexibility and complexity.

[0008] In general, the larger the antenna array and the wider the signal bandwidth, the more attractive analog beamforming becomes. This means that at high operating frequencies where the signal bandwidths are higher and larger array sizes are required, analog beamforming is preferred. There is a trend in fifth-generation (5G) and sixth-generation (6G) wireless communications networks toward high operating frequencies and high bandwidths.

[0009] There are different analog beamforming architectures, which can be separated by where the phase shift is performed. The phase shift can be performed on the RF signal - so called RF beamforming, on the local oscillator (LO) signal - so called LO beamforming, and on the baseband signal - so called analog baseband beamforming. All have in common that the signal is phase shifted, rather than having TTD.

[0010] Implementing TTD with delay elements in analog electronics is very complicated and costly due to numerous reasons, such as, increased area consumption, increased loss, and non-uniform delay and amplitude frequency transfer functions of delay elements. Therefore, the time delay t in the equation above is typically not implemented as a TTD in analog beamforming. Instead, it is approximated by the corresponding phase shift at the center frequency of the channel of transmission or reception.

[0011] In Figure 2, each antenna element 211 :214 is provided with a respective branch for providing a signal to and receiving a signal from the corresponding antenna element. Each branch is provided with means 221 :224 to phase shift the signal at the center frequency of the channel of transmission or reception. The signal is shifted by <p±for antenna element 211 , the signal is shifted by p2for antenna element 212, the signal is shifted by p3for antenna element 213, and the signal is shifted by p4for antenna element 214. To provide the intended beam direction 0 from boresight, the phases may be selected as <p4= 0, <p2= A^, <p2= 2A¥ / , <p4= 3AV7, where AV7= —d sin d A where A is the wavelength at the center frequency of the channel of transmission or reception.

[0012] While this approximation is correct at the center frequency, it does not correspond to the correct time delay at other frequencies. For lower frequencies it will correspond to more time delay and for higher frequencies it will correspond to less. This results in that the direction giving positive interference, i.e. the beam direction, will vary with the absolute frequency within the channel, which is called beam squint. For channels with relatively small bandwidth, or small beam steering angles 0, or small array sizes, the beam squint will in many cases be neglectable. However, when increasing the relative bandwidth of communication and / or when increasing the array size and beam steering angles, the errors resulting from beam squint become significant. As analog beamforming is most attractive for large array sizes and wide signal bandwidths, such as at high operating frequencies in 5G and 6G, this becomes an increasingly important obstacle to overcome.

[0013] SUMMARY

[0014] It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages in the prior art and solve at least the above- mentioned problem. It is an object to provide improved wireless communications systems. In particular, it is an object to provide improved ways of handling beam squint.

[0015] This object is obtained at least in part by a transmitter for transmitting radio frequency (RF) signals via an antenna array comprising a plurality of antenna elements. The transmitter comprises N branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements, where N is an integer larger than 1. Each branch of the N branches comprises M mixers, where M is an integer larger than 1. In each branch of the N branches, each mixer of the M mixers is configured to receive a respective analog sub-band baseband signal and upconvert said respective analog sub-band baseband signal to a respective sub-band RF signal. In each branch of the N branches, the M mixers are configured to introduce a difference in phase between each of the M sub-band RF signals. Furthermore, each branch of the N branches comprises a respective combiner configured to combine M sub-band RF signals of that branch to one of the respective RF signals.

[0016] The M mixers of each branch of the disclosed transmitter enable a reduction of the effect of beam squint. The reduced beam squint, in turn, enables an increased signal bandwidth. The disclosed transmitter provides these benefits with a practical power consumption. Thus, the disclosed transmitter provides improved wireless communications systems, particularly at mm- wave frequencies of 5G and 6G. The disclosed transmitter does not require analog delay elements, which provides a flexible beam steering. Each mixer of the disclosed transmitter delivers less signal power than a corresponding full-band mixer. Thus, the size of the individual mixers can be scaled down, which reduces power consumption overhead.

[0017] Furthermore, in contrast to RF phase shifting, using the mixers for phase shifting enables a simpler topology, which is advantageous. The RF signal is wideband, whereas the LO signal only contains a single tone. It is therefore easier to perform the phase shift on the LO signal compared to at RF. With a single tone there is no intermodulation distortion in the LO phase shifters and hence no linearity requirements. Also there are no requirements on bandwidth of frequency transfer functions of amplitude and phase.

[0018] There is also disclosed herein, a method, by a transmitter, for enabling transmission of RF signals via an antenna array comprising a plurality of antenna elements. The transmitter comprises N branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements, where N is an integer larger than 1. This disclosed method is associated with the above-discussed advantages of the disclosed transmitter. The method comprises obtaining, for each branch of the N branches, M analog sub-band baseband signals, where M is an integer larger than 1. The method further comprises upconverting, for each branch of the N branches, each of the M analog sub-band baseband signals to respective subband RF signals with a difference in phase. The method also comprises combining, for each branch of the N branches, M sub-band RF signals to one of the respective RF signals.

[0019] There is also disclosed herein, a receiver for receiving RF signals via an antenna array comprising a plurality of antenna elements. The receiver comprises N branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements, where N is an integer larger than 1. Each branch of the N branches comprises M mixers, where M is an integer larger than 1 . Each branch of the N branches comprises a respective splitter configured to split the RF signal received by that branch to the M mixers of that branch. In each branch of the N branches, each mixer of the M mixers is configured to receive the RF signal received by the corresponding branch and downconvert said RF signal to an analog baseband signal. Furthermore, in each branch of the N branches, the M mixers are configured to introduce a difference in phase between each of the analog baseband signals.

[0020] The M mixers of each branch of the disclosed receiver enable a reduction of the effect of beam squint. The reduced beam squint, in turn, enables an increased signal bandwidth. The disclosed receiver provides these benefits with a practical power consumption. Thus, the disclosed receiver provides improved wireless communications systems, particularly at mm- wave frequencies of 5G and 6G. The disclosed receiver does not require analog delay elements, which provides a flexible beam steering. Each mixer of the disclosed receiver delivers less signal power than a corresponding full-band mixer. Thus, the size of the individual mixers can be scaled down, which reduces power consumption overhead. Furthermore, in contrast to RF phase shifting, using the mixers for phase shifting enables a simpler topology, which is advantageous.

[0021] There is also disclosed herein, a method, by a receiver, for enabling reception of RF signals via an antenna array comprising a plurality of antenna elements. The receiver comprises N branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements, where N is an integer larger than 1. This disclosed method is associated with the above-discussed advantages of the disclosed receiver. The method comprises obtaining, for each branch of the N branches, a respective RF signal. The method also comprises splitting, for each branch of the N branches, the obtained RF signal to M RF signals, where M is an integer larger than 1. The method further comprises downconverting, for each branch of the N branches, each of the M RF signals to respective analog baseband signals with a difference in phase.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS

[0023] With reference to the appended drawings, below follows a more detailed description of embodiments of the present disclosure cited as examples. In the drawings:

[0024] Figure 1 is a schematic illustration of a wireless communications network;

[0025] Figure 2 shows a transceiver with four branches;

[0026] Figure 3 shows a branch of a transmitter with two paths;

[0027] Figure 4 shows a branch of a receiver with two paths;

[0028] Figures 5-8 show different receiver topologies;

[0029] Figure 9A shows a Gilbert-cell-based mixer with frequency up-conversion for a single data stream;

[0030] Figure 9B shows a Gilbert-cell-based mixer with frequency up-conversion for combination of two data streams;

[0031] Figure 10 shows a branch of a transmitter with N paths;

[0032] Figures 11 and 12 show antenna gain versus frequency;

[0033] Figures 13 and 14 are flow charts illustrating methods;

[0034] Figure 15 schematically illustrates a transmitter; and

[0035] Figure 16 schematically illustrates a receiver.

[0036] DETAILED DESCRIPTION

[0037] The present disclosure is described below with reference to the accompanying drawings, in which certain aspects of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments and aspects set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.

[0038] It is to be understood that the present disclosure is not limited to the embodiments described herein and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

[0039] Figure 1 depicts a wireless communications network 100 in which embodiments herein may operate. In some embodiments, the wireless communications network 100 may be a radio communications network, such as, 6G, NR or NR+ telecommunications network. However, the wireless communications network 100 may also employ technology of any one of 3 / 4 / 5G, LTE, LTE-Advanced, WCDMA, GSM / EDGE, WiMax, UMB, GSM, or any other similar network or system. The wireless communications network 100 may also employ technology transmitting on millimeter-waves (mmW), such as, e.g. an Ultra Dense Network, UDN. In some embodiments, the wireless communications network 100 may also employ transmissions supporting WiFi transmissions, e.g. the wireless communications standard IEEE 802.11ad or similar, or other non-cellular wireless transmissions.

[0040] The wireless communications network 100 comprises a network node 110. The network node 110 may serve wireless devices in at least one cell 115, or coverage area. The network node 110 may correspond to any type of network node or radio network node capable of communicating with a wireless device and / or with another network node, such as, a base station (BS), a radio base station, gNB, eNB, eNodeB, a Home NodeB, a Home eNodeB, a femto Base Station (BS), or a pico BS in the wireless communications network 100. Further examples of the network node 110 may be a repeater, multi-standard radio (MSR) radio node such as MSR BS, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, a Remote Radio Unit (RRU), a Remote Radio Head (RRH), nodes in distributed antenna system (DAS), or core network node. The network node 110 may be arranged to communicate with a remote data processing unit 140 via a core network 150 of the wireless communications network 100. The remote data processing unit 140 may, for example, be a remote standalone server, a cloud-implemented server, a distributed server, dedicated data processing resources in a server farm, or similar.

[0041] Furthermore, in Figure 1 , a wireless device 121 is located within the cell 115. The wireless device 121 is configured to communicate within the wireless communications network 100 via the network node 110 over a radio link served by the network node 110. The wireless device 121 may transmit data over an air or radio interface to the radio base station 110 in uplink (UL), transmissions 132 and the radio base station may transmit data over an air or radio interface to the wireless device 121 in downlink (DL) transmissions 131. The wireless device 121 may refer to any type of wireless devices or user equipment (UE) communicating with a network node and / or with another wireless device in a cellular, mobile or radio communication network or system. Examples of such wireless devices are mobile phones, cellular phones, personal digital assistants (PDAs), smart phones, tablets, sensors equipped with a UE, laptop mounted equipment (LME) (e.g. Universal Serial Bus, USB), laptop embedded equipment (LEE), machine type communication (MTC) devices, or machine to machine (M2M) device, customer premises equipment (CPE), target device, device-to-device (D2D) wireless device, wireless device capable of machine to machine (M2M) communication.

[0042] As mentioned, analog beamforming is desirable for large array sizes and wide signal bandwidths, such as at high operating frequencies in 5G and 6G. Thus, beam squinting becomes an increasingly important obstacle to overcome. When developing the embodiments disclosed herein, it has been realized that it is possible to divide the signal into sub-bands that are individually phase shifted to reduce beam squinting, and that such an architecture can be implemented using sub-band filtering in the baseband with analog or digital filters, where the phase shifting may be provided by the mixers, i.e. , LO beamforming.

[0043] In particular, an analog baseband signal may be represented by two or more frequency adjacent analog sub-band baseband signals, each with half, or less, signal bandwidth of the baseband signal. LO beamforming is used with separate mixers for each sub-band baseband signal. The mixers may operate with the same LO frequency, but with different LO signal phases. The phase shifts of the mixers may be set according to intended beam direction for the center frequency of each RF sub-band (where an RF sub-band corresponds to a baseband sub-band as upconverted). As the bandwidth of each sub-band baseband signal is less than the full bandwidth by a factor of two or more compared to the (full, wideband) baseband signal, the beam squint problem is reduced accordingly. This enables wider relative signal bandwidth, larger array sizes, and larger beam steering angles in analog beamforming systems.

[0044] In each branch of a transmitter, the signals of the mixers are combined before transmission by an antenna element. In an example of a branch of a receiver, the signals from the mixers are processed in analog complex filters to reject signals outside the sub-bands before combination to the (more wideband, and complete) baseband signal, with subsequent processing with signals from the other antenna branches.

[0045] Figure 3 shows an example transmitter 300 according to embodiments disclosed herein. Although the transmitter 300 disclosed herein comprises two or more branches, Figure 3 only shows a single branch for improved visibility. Each branch is configured to provide a respective RF signal to a respective antenna element, such as one of the antenna elements 211 :214 of the antenna array 210 of Figure 2. The respective RF signals transmitted by the antenna elements comprise the same baseband signal (as upconverted) that has been shifted differently in phase to obtain an intended beam steering of the antenna array.

[0046] To summarize, there is disclosed herein a transmitter 300 for transmitting RF signals via an antenna array 210 comprising a plurality of antenna elements 211 :214. The transmitter 300 comprises N branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements 211 :214, where N is an integer larger than 1.

[0047] An antenna element is an element capable of radiating and / or receiving electromagnetic energy. An antenna array is a structure with a plurality of antenna elements arranged in an intended pattern. In particular, the antenna array 210 comprises at N antenna elements. The antenna elements may be equidistantly arranged in one or two dimensions. As an example, the distance between antenna elements may be 2 / 2, which results in the possibility to form one main beam without significant side lobes. Other distances are also possible.

[0048] In Figure 3, the branch comprises two paths with respective mixers, i.e., mixers 304 and 305. In particular, the mixers 304, 305 comprise respective in-phase and quadrature (IQ) mixers. Each mixer 304, 305 is configured to receive a respective analog sub-band baseband signal and upconvert said respective analog sub-band baseband signal to a respective subband RF signal.

[0049] A baseband signal may be divided into a plurality of sub-bands. For example, a 20-MHz baseband signal may be divided into two frequency-adjacent and non-overlapping 10-MHz sub-bands.

[0050] Each analog sub-band baseband signal comprises a sub-band of the same baseband signal. In other words, each analog sub-band baseband signal comprises a portion (i.e., fraction) of the frequency content of the same baseband signal.

[0051] In each branch, all analog sub-band baseband signals are preferably different sub-bands of the baseband signal. In other words, each sub-band baseband signals may comprise respective sub-bands of an analog baseband signal. In each branch, all analog sub-band baseband signals are preferably non-overlapping sub-bands of the baseband signal. However, it is also possible that the analog sub-band baseband signals are overlapping sub-bands of the baseband signal. Moreover, all analog sub-band baseband signals in a given branch may comprise respective frequency-adjacent sub-bands of the analog baseband signal.

[0052] In Figure 3, a baseband signal is divided into two sub-bands: BB1 and BB2, which are nonoverlapping and frequency adjacent. BB1 and BB2 comprise respective halves of the frequency content of the baseband signal. A digital representation of BB1 is provided to an input 312 of a DAC 310, which converts the input to one of the respective analog sub-band baseband signals. Thereafter, the analog sub-band baseband signal propagates along a baseband path 308 until it reaches an input of the mixer 304. The baseband path 308 represents the signal propagation path between the DAC 310 and the mixer 304. Note that the DAC 310 and the baseband path 308, which typically comprises filters, can be shared between several transmitter paths. A digital representation of BB2 is provided to an input 313 of a DAC 311 , which converts the input to one of the respective analog sub-band baseband signals. Thereafter, the analog sub-band baseband signal propagates along a baseband path 309 until it reaches an input of the mixer 305. The baseband path 309 represents the signal propagation path between the DAC 311 and the mixer 305. Note that the DAC 311 and the baseband path 309, which typically comprises filters, can be shared between several transmitter paths

[0053] The mixer 304 is fed by an LO signal, which is a single tone signal. The LO signal fed to mixer 304 is controlled in phase, by a variable phase shift unit 306, with respect to other LO signals fed to other mixer of the transmitter 300. The phase of the LO signal fed to mixer 304 is denoted <P1.

[0054] The mixer 305 is fed by an LO signal, which is a single tone signal. The LO signal fed to mixer 305 is controlled in phase, by a variable phase shift unit 307, with respect to other LO signals fed to other mixers of the transmitter 300. The phase of the LO signal fed to mixer 305 is denoted <P2.

[0055] When the transmitter 300 is configured to direct the beam of the antenna array different than boresight, the mixers 304, 305 are configured to introduce a difference in phase between the two sub-band RF signals. Thus, <P±is different from <P2. The difference in phase may be configured based on beam directions of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210. In particular, the difference in phase may be configured based on beam directions of the respective center frequency of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210.

[0056] As an example, an RF signal to be transmitted by an antenna element of a branch may have a center frequency of 100 GHz and a bandwidth of 10 GHz. In a prior art transmitter, where the branch comprises a single path and no splitting of the baseband signal, it may e.g. be determined to phase shift the RF signal of that branch by 100 degrees (relative to other branches). This phase shift is typically chosen to provide the desired beam direction at the center frequency of the RF signal (i.e. 100GHz in this example). However, at other frequencies in the channel bandwidth, particularly at the edges (i.e. at 95GHz and 105GHz in this example), other phase shifts may be needed to steer the beam in the same direction. In the transmitter 300 of Figure 3 however, the RF signal may comprise a first RF sub-band of 95 to 100 GHz and a second RF sub-band of 100 to 105 GHz, where the first RF sub-band has been phase shifted by e.g. 90 degrees at 97.5 GHz, and the second RF sub-band been has phase shifted by e.g. 110 degrees at 102.5 GHz, to form a beam in the desired direction at the center frequencies of both sub-bands, i.e. at 97.5GHz and 102.5GHz, to reduce the variation in beam direction for the different frequencies of the transmitted signal.

[0057] In Figure 3, it can be seen that the branch further comprises a combiner 303 that is configured to combine the two sub-band RF signals to one of the respective RF signals to be transmitted by an antenna element of the antenna array. The combiner 303 may also be called a power combiner. The combiner may be isolating or non-isolating.

[0058] Before the mixer 304, it can be seen that the sub-band BB1 is located at DC. After upconversion by the mixer 304, it can be seen that the sub-band BB1 is located at the carrier frequency of the LO signal (denoted “LO” in Figure 3). Similarly, before the mixer 305, it can be seen that the sub-band BB2 is located at DC. After upconversion by the mixer 305, it can be seen that the sub-band BB2 is located at the carrier frequency of the LO signal.

[0059] After the combiner 303, both BB1 and BB2 are present in the spectrum at the carrier frequency of the LO signal. As is shown in Figure 3, the branch may comprise a power amplifier (PA) 302. In particular, after the combiner 303, the RF signal comprising both sub-bands is amplified by the PA 302, which increases the power of the signal before reaching antenna element 301.

[0060] Each branch of the transmitter 300 may comprise two or more paths. Thus, in general, each branch of the N branches comprises M mixers 304, 305, where M is an integer larger than 1. In each branch of the N branches, each mixer of the M mixers 304, 305 is configured to receive a respective analog sub-band baseband signal and upconvert said respective analog subband baseband signal to a respective sub-band RF signal. In each branch of the N branches, the M mixers 304, 305 are configured to introduce a difference in phase between each of the M sub-band RF signals. Each branch of the N branches comprises a respective combiner 303 configured to combine M sub-band RF signals of that branch to one of the respective RF signals.

[0061] The M mixers of each branch of the transmitter 300 enable a reduction of the effect of beam squint. The reduced beam squint, in turn, enables an increased signal bandwidth. The transmitter 300 provides these benefits with a practical power consumption. Thus, the transmitter 300 provides improved wireless communications systems, particularly at mm-wave frequencies of 5G and 6G. The transmitter 300 does not require analog delay elements, which provides a flexible beam steering. Each mixer of the transmitter 300 delivers less signal power than a corresponding full-band mixer. Thus, the size of the individual mixers can be scaled down, which reduces power consumption overhead. In each branch of the N branches, M analog sub-band baseband signals may comprise respective sub-bands of an analog baseband signal. In other words, in each branch of the N branches, M analog sub-band baseband signals may comprise different sub-bands of an analog baseband signal. The different sub-bands are preferably non-overlapping. In particular, in each branch of the N branches, M analog sub-band baseband signals may comprise respective frequency-adjacent sub-bands of the analog baseband signal.

[0062] In each branch of the N branches, each mixer of the M mixers 304, 305 may be configured to mix a respective received analog sub-band baseband signal with a respective LO signal, where each of the respective LO signals is associated with a carrier frequency and a difference in phase. In other words, each of the LO signals have the same carrier frequency. In contrast to RF phase shifting, the LO phase shifting of the transmitter 300 provides a simpler topology, which is advantageous. The RF signal is wideband, whereas the LO signal only contains a single tone. It is therefore easier to perform the phase shift on the LO signal compared to at RF. With a single tone there is no intermodulation distortion in the LO phase shifters and hence no linearity requirements. Also there are no requirements on bandwidth of frequency transfer functions of amplitude and phase.

[0063] Furthermore, using a single carrier frequency of the LO signals reduces pulling issues. Using a single carrier frequency reduces problems that could arise when using multiple carrier frequencies that are close to each other. For instance, oscillators operating at nearby frequencies are prone to couple to each other and cause disturbances to each other, so called pulling. Such disturbances can degrade the quality of the transmitted signal, as well as cause disturbances to communication in neighbouring frequency channels.

[0064] In each branch of the N branches, the difference in phase may be configured based on beam directions of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210. In particular, the difference in phase may be configured based on intended beam directions of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210. Furthermore, the difference in phase may be configured based on beam directions of the respective center frequencies of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210. As an example, each branch of the N branches may be associated with a unique delay value. The phase of the respective LO signals of a branch may be selected such that the respective center frequencies of the sub-bands of the RF signal to be transmitted by the antenna element of that branch is shifted in phase corresponding to the unique delay value of that branch (relative to other branches). It should be noted that in large arrays for large beam steering angles, the delay can correspond to multiple carrier signal periods, and the conversion from time to corresponding phase then contains removing the integer number of signal periods. For instance, if the delay is 2.1 carrier signal periods at one sub-band center frequency, the corresponding phase is calculated by removing the integer number of periods (which is equal to 2 in this case), resulting in 0.1 periods, from which the corresponding phase can be calculated as 0.1*360=36 degrees.

[0065] In each branch of the N branches, each mixer of the M mixers 304, 305 may comprise a respective IQ mixer.

[0066] The transmitter 300 may be configured to obtain, for each branch of the N branches, M analog sub-band baseband signals. Alternatively, the transmitter may comprise one or more DACs to provide the sub-band baseband signals. In particular, the transmitter 300 may comprise respective DACs 310, 311 arranged to convert respective digital sub-band baseband signals to the M analog sub-band baseband signals.

[0067] The transmitter 300 may comprise additional components conventionally found in a transmitter. For example, each branch may comprise respective PAs, variable gain amplifiers, and respective filters.

[0068] There is also disclosed herein a transmitter system comprising the transmitter 300 and the antenna array 210. In the transmitter system, each branch of the N branches provides a respective RF signal to respective antenna elements of the plurality of antenna elements 211 :214 of the antenna array 210.

[0069] Figure 4 shows an example receiver 400 according to embodiments disclosed herein. Although the receiver 400 disclosed herein comprises two or more branches, Figure 4 only shows a single branch for improved visibility. Each branch is configured to receive a respective RF signal from a respective antenna element, such as one of the antenna elements 211 :214 of the antenna array 210 of Figure 2. The respective RF signals received by the antenna elements comprise the same baseband signal (as upconverted) that will be shifted differently in phase to obtain an intended beam steering of the antenna array.

[0070] To summarize, there is disclosed herein a receiver 400 for receiving RF signals via an antenna array 210 comprising a plurality of antenna elements 211 :214. The receiver 400 comprises N branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements 211 :214, where N is an integer larger than 1.

[0071] In Figure 4, it can be seen that the branch of the receiver 400 comprises two paths with respective mixers, viz., mixers 404 and 405. It can further be seen that the branch of the receiver 400 comprises a splitter 403 configured to split the RF signal received by the antenna element 401 of the branch to the mixers 404, 405. Each of the mixers 404, 405 is configured to receive the RF signal received by the antenna element 401 of the branch and downconvert said RF signal to an analog baseband signal. In particular, the mixers 404, 405 comprise respective IQ mixers. The output of the mixer 404, which provides a downconverted signal, is denoted 408. The output of the mixer 405, which provides a downconverted signal, is denoted 409.

[0072] The RF signal as received by antenna element 401 may be divided into a plurality of subbands. For example, a 20-MHz baseband signal carried on an RF carrier may be divided into two frequency-adjacent and non-overlapping 10-MHz sub-bands at the RF carrier.

[0073] Each sub-band of the RF signal comprises a sub-band of the same baseband signal as carried on the RF carrier. In other words, each sub-band of the RF signal comprises a portion (i.e., fraction) of the frequency content of the same baseband signal as carried on the RF carrier.

[0074] All sub-bands of the RF signal are preferably different sub-bands of the baseband signal as carried on the RF carrier. In other words, each sub-band may comprise a respective sub-band of the baseband signal as carried on the RF carrier. All sub-bands of the RF signal are preferably non-overlapping sub-bands of the baseband signal as carried on the RF carrier. However, it is also possible that sub-bands of the RF signal are overlapping sub-bands of the baseband signal as carried on the RF carrier. Moreover, all sub-bands of the RF signal baseband signal in a given branch may comprise respective frequency-adjacent sub-bands of the baseband signal as carried on the RF carrier.

[0075] In Figure 4, an RF signal is obtained via antenna element 401. The received RF signal comprises sub-bands BB1 and BB2 at a carrier frequency, i.e., an RF carrier (denoted LO). BB1 and BB2 are non-overlapping and frequency adjacent. BB1 and BB2 comprise respective halves of the frequency content of a baseband signal as carried on the RF carrier.

[0076] As is shown in Figure 4, the branch may comprise a low noise amplifier (LNA) 402. In particular, after the reception of the RF signal by antenna element 401 , the RF signal comprising both sub-bands is amplified by the LNA 402, which increases the power of the signal before reaching a splitter 403. The splitter 403 splits the RF signal, as amplified by the LNA 401 , into the mixers 404, 405. The splitter 403 may also be called a power splitter. The splitter may be isolating or non-isolating.

[0077] The mixer 404 is fed by an LO signal, which is a single tone signal. The LO signal fed to mixer 404 is controlled in phase, by a variable phase shift unit 406, with respect to other LO signals fed into other mixers of the receiver 400. The phase of the LO signal fed to mixer 404 is denoted <P1.

[0078] The mixer 405 is fed by an LO signal, which is a single tone signal. The LO signal fed into mixer 405 is controlled in phase, by a variable phase shift unit 407, with respect to other LO signals fed into other mixer of the receiver 400. The phase of the LO signal fed into mixer 405 is denoted <P2- When the receiver 400 is configured to direct the beam of the antenna array different than boresight, the mixers 404, 405 are configured to introduce a difference in phase between the two paths (i.e. , between the two signals as downconverted by the mixers 404, 405). Thus, <P±is different from <P2- The difference in phase may be configured based on beam directions of the sub-band RF signals as comprised in the RF signals to be received by the antenna array 210. In particular, the difference in phase may be configured based on beam directions of the respective center frequency of the sub-band RF signals as comprised in the RF signals to be received by the antenna array 210.

[0079] As an example, an RF signal to be received by an antenna element of a branch may have a center frequency of 100 GHz and a bandwidth of 10 GHz. In a prior art receiver, where the branch comprises a single path and no splitting of the RF signal, it may e.g. be determined to phase shift the RF signal of that branch by 100 degrees (relative to other branches). This phase shift is typically chosen to provide the desired beam direction at the center frequency of the RF signal (i.e. 100GHz in this example). However, at other frequencies in the channel bandwidth, particularly at the edges (i.e. at 95GHz and 105GHz in this example), other phase shifts may be needed to steer the beam in the same direction. In the receiver 400 of Figure 4 however, the RF signal may be treated as comprising two sub-bands, namely, a first RF subband (BB1) of 100 to 105 GHz and a second RF sub-band (BB2) of 95 to 100 GHz. The mixer 404 may be configured such that its downconverted signal is phase shifted by e.g. 90 degrees, and the mixer 405 may be configured such that its downconverted signal is phase shifted by e.g. 110 degrees. By using the BB1 baseband frequencies (0 to 5MHz) from mixer 404 and the BB2 baseband frequencies (-5MHz to 0) from mixer 405, a receive beam can be formed in the desired direction at the center frequencies of both RF sub-bands, i.e. at 97.5GHz and 102.5GHz, to reduce the variation in beam direction for the different frequencies of the received signal.

[0080] In Figure 4, it can be seen that the RF signal received by antenna element 401 comprises sub-bands BB1 and BB2 at the RF frequency (denoted LO). After the LNA, the signal is amplified. After the mixer 404, the signal as downconverted comprises sub-bands BB1 and BB2 located at DC. After the mixer 405, the signal as downconverted comprises sub-bands BB1 and BB2 located at DC.

[0081] Each branch of the receiver 400 may comprise two or more paths. Thus, in general each branch of the N branches comprises M mixers 404, 405, where M is an integer larger than 1 . Each branch of the N branches comprises a respective splitter 403 configured to split the RF signal received by that branch to the M mixers 404, 405 of that branch. In each branch of the N branches, each mixer of the M mixers 404, 405 is configured to receive the RF signal received by the corresponding branch and downconvert said RF signal to an analog baseband signal. In each branch of the N branches, the M mixers 404, 405 are configured to introduce a difference in phase between each of the analog baseband signals.

[0082] The M mixers of each branch of the receiver 400 enable a reduction of the effect of beam squint. The reduced beam squint, in turn, enables an increased signal bandwidth. The receiver 400 provides these benefits with a practical power consumption. Thus, receiver 400 provides improved wireless communications systems, particularly at mm-wave frequencies of 5G and 6G. The receiver 400 does not require analog delay elements, which provides a flexible beam steering.

[0083] For each branch of the N branches, each of the M analog baseband signals comprise M analog sub-band baseband signals. In other words, in each branch of the N branches, each of the M analog baseband signals may comprise different sub-bands of an analog baseband signal. The different sub-bands are preferably non-overlapping. In particular, the M analog subband baseband signals may be respective frequency-adjacent sub-bands.

[0084] In each branch of the N branches, each mixer of the M mixers 404, 405 may be configured to mix a respective received RF signal with a respective LO signal, where each of the respective LO signals is associated with a carrier frequency and a difference in phase. In other words, each of the LO signals have the same carrier frequency. In contrast to RF phase shifting, the LO phase shifting of the receiver 400 provides a simpler topology, which is advantageous. Furthermore, using a single carrier frequency of the LO signals reduces pulling issues.

[0085] In each branch of the N branches, the difference in phase may be configured based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210. In particular, the difference in phase may be configured based on intended beam directions the sub-band RF signals as comprised in the RF signals to be received by the antenna array 210. Furthermore, the difference in phase may be configured based on beam directions of the respective center frequencies of the sub-band RF signals as comprised in the RF signals to be received by the antenna array 210. As an example, for a certain beam steering angle, each branch of the N branches may be associated with a unique delay value. The phase of the respective LO signals of a branch may be selected such that the phase of the respective center frequencies of the sub-bands of the RF signal to be received by the antenna element of that branch corresponds to the unique delay value of that branch (relative to other branches). It should be noted that in large arrays for large beam steering angles, the delay can correspond to multiple carrier signal periods, and the conversion from time to corresponding phase then contains removing the integer number of signal periods. For instance, if the delay is 2.1 carrier signal periods at one sub-band center frequency, the corresponding phase is calculated by removing the integer number of periods (which is equal to 2 in this case), resulting in 0.1 periods, from which the corresponding phase can be calculated as 0.1*360=36 degrees.

[0086] In each branch of the N branches, each mixers of the M mixers 404, 405 may comprise a respective IQ mixer.

[0087] The receiver 400 may comprise additional components conventionally found in a receiver. For example, each branch may comprise respective LNAs, respective variable gain amplifiers, and respective filters.

[0088] There is also disclosed herein a receiver system comprising the receiver 400 and the antenna array 210. In the receiver system, each branch of the N branches receives a respective RF signal from respective antenna elements of the plurality of antenna elements 211 :214 of the antenna array 210.

[0089] The transmitter 300 and the receiver 400 may be part of a single transceiver. Furthermore, there is also disclosed herein a communication apparatus comprising the transmitter 300, the transmitter system, the receiver 400, and / or the receiver system. The communication apparatus may, e.g., be a wireless communications device 121 for a wireless communications network, such as the wireless communications device 121 shown in Figure 1. Alternatively, the communication apparatus may be a network node 110 for a wireless communications network, such as the network node 110 shown in Figure 1

[0090] In Figure 4, the signal at output 408 has been shifted in phase differently compared to the signal in at output 409. In particular, the signal at output 408 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB1 , and the signal at output 409 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB2. It is desired to process these two signals separately and thereafter combine them to reduce the effects of beam squint. Such processing can be done in several different ways. For example, the signals from the mixers can be processed in analog complex filters to reject signals outside the sub-bands before combination to a wideband baseband signal, and further processing with signals from the other antenna branches. Alternatively, each sub-band signal may be processed separately in the receiver, where branch signals of each sub-band are combined and fed to separate ADCs, where sub-band filtering and combination is performed in the digital domain. Figures 5-8 show four different embodiments of processing the signals from each branch of the receiver. These figures are discussed in more detail below.

[0091] Figure 5 shows a first embodiment of processing the signals from each branch of the receiver 400. This embodiment may be called an “M ADC embodiment” since M ADCs are required. Particularly, one ADC per path is required. It may be noted that each baseband signal ADC can consist of a pair of ADCs, one for the in-phase (I) part of the signal and one for the quadrature (Q) part of the signal, so the total number of ADCs is then 2*M.

[0092] The first embodiment comprises M primary combiners, illustrated by the two primary combiners 503 and 504 in Figure 5. Each primary combiner is configured to combine a respective signal from a mixer of each branch. Each primary combiner provides a combined signal (which is in the analog domain) to a respective ADC. The respective digital representations of the combined signals are thereafter fed into respective digital filters, which filters the combined signal with respect to one of the sub-band baseband signals. In particular, each digital filter filters a signal such that the filtered signal only comprises one of the subbands of the M sub-bands. All filtered signals are combined by a secondary combiner into a (wideband) baseband signal.

[0093] Which respective paths from the respective branches that is fed into one of the primary combiners is selected based on which of the sub-bands the digital filter is configured to filter with respect to.

[0094] Although M can be any integer larger than 1 , Figure 5 shows the case when M=2 for improved visibility.

[0095] At the top of Figure 5, a primary combiner 503 combines respective signal from a mixer of each branch. The signal from a mixers is a complex baseband signal consisting of I and Q signals. The signal path from said mixers into the primary combiner 503 is denoted 501. In particular, the complex baseband signals provided to the primary combiner 503 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB1. The combined signal from the primary combiner 503 is provided to an ADC 505. The digital signal from ADC 505 is provided to a digital filter 507, which filters the digital signal with respect to the sub-band BB1. In particular, the digital filter 507 rejects all frequencies other than those constituting the sub-band BB1.

[0096] At the bottom of Figure 5, a primary combiner 504 combines respective signal from a mixer of each branch. The signal path from said mixers into the primary combiner 504 is denoted 502. In particular, the signals provided to the primary combiner 504 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB2. The combined signal from the primary combiner 504 is provided to an ADC 506. The digital signal from ADC 506 is provided to a digital filter 508, which filters the digital signal with respect to the sub-band BB2. In particular, the digital filter 508 rejects all frequencies other than those constituting the sub-band BB2.

[0097] The filtered signal from the digital filter 507 is combined with the filtered signal from the digital filter 508 by a secondary combiner 509. The output of the secondary combiner 509 is denoted 510 and comprises a (wideband) digital baseband signal comprising both the sub- bands BB1 and BB2. The signal at 510 thus comprises a baseband signal provided via an intended beam steering of the antenna array 210 with reduced beam squint as compared to prior art receivers.

[0098] To summarize, the receiver 400 may comprise M primary combiners 503, 504. Each primary combiner of the M primary combiners 503, 504 is configured to combine analog baseband signals from a respective mixer of the M mixers 404, 405 from each branch of the N branches. The receiver 400 may further comprise M ADCs 505, 506, where each ADC of the M ADCs 505, 506 is configured to convert a respective combined analog baseband signal from a respective primary combiner of the M primary combiners 503, 504 to a respective digital baseband signal. The receiver 400 may further comprise M digital filters 507, 508, where each digital filter of the M digital filters 507, 508 is configured to filter a respective digital baseband signal with respect to a respective baseband sub-band. The receiver 400 may further comprise a secondary combiner 509 configured to combine the filtered digital baseband signals.

[0099] As mentioned, when the receiver 400 is configured to direct the beam of the antenna array different than boresight, the mixers of a particular branch are configured to introduce a difference in phase relative to each other and relative to the mixers of other branches. When the beam is steered far from boresight (e.g. more than 50 degrees), it may be desired to configure each digital filter to highly attenuate all sub-bands but one (e.g., provide an attenuation of more than 20 dB). However, when the beam is steered close to boresight (e.g. less than 10 degrees), it may be desired to configure each digital filter to attenuate all subbands but one less compared to the case when the beam is steered far from boresight. In other words, each digital filter of the M digital filters 507, 508 may be configured to filter the respective digital baseband signal based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210.

[0100] Figure 6 shows a second embodiment of processing the signals from each branch of the receiver 400. This embodiment may be called a “single ADC embodiment” since only a single ADC is required. It may be noted that the single ADC can consist of a pair of ADCs, one for the in-phase (I) part of the signal and one for the quadrature (Q) part of the signal.

[0101] The second embodiment comprises M primary combiners. Each primary combiner is configured to combine a respective signal from a mixer of each branch. Each primary combiner provides a combined signal (which is in the analog domain) to a respective analog filter, which filters the combined signal with respect to one of the sub-band baseband signals. In particular, each analog filter filters a signal such that the filtered signal “only” comprises one of the subbands of the M sub-bands (note that some frequency content of the rejected bands may be present since the rejection is non-perfect in practice). All filtered signals are combined by a secondary combiner into a (wideband) baseband signal (also in the analog domain). The signal provided by the secondary combiner is provided to an ADC.

[0102] As mentioned in connection to Figure 5, which respective paths from the respective branches that is fed into one of the primary combiners is selected based on which of the subbands the filter (analog filter in the case of Figure 6) is configured to filter with respect to.

[0103] Although M can be any integer larger than 1 , Figure 6 shows the case when M=2 for improved visibility.

[0104] At the top of Figure 6, a primary combiner 603 combines respective signal from a mixer of each branch. The signal path from said mixers into the primary combiner 603 is denoted 601. In particular, the signals provided to the primary combiner 603 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB1. The combined signal from the primary combiner 603 is provided to an analog filter 605, which filters the signal with respect to the sub-band BB1. In particular, the analog filter 605 may reject all frequencies other than those constituting the sub-band BB1 . Note that the analog filter 605 is a complex bandpass filter.

[0105] At the bottom of Figure 6, a primary combiner 604 combines respective signal from a mixer of each branch. The signal path from said mixers into the primary combiner 604 is denoted 602. In particular, the signals provided to the primary combiner 604 may have been shifted in phase (relative to other branches) that is particularly suitable for the sub-band BB2. The combined signal from the primary combiner 604 is provided to an analog filter 606, which filters the signal with respect to the sub-band BB2. Note that the analog filter 606 is a complex bandpass filter. In particular, the analog filter 606 may reject all frequencies other than those constituting the sub-band BB2.

[0106] The filtered signal from the analog filter 605 is combined with the filtered signal from the analog filter 606 by a secondary combiner 607. The combined signal from the secondary combiner 607 is provided to an ADC 608. The output of the ADC 608 is denoted 609 and comprises a (wideband) digital baseband signal comprising both the sub-bands BB1 and BB2. The signal at 609 thus comprises a baseband signal provided via an intended beam steering of the antenna array 210 with reduced beam squint as compared to prior art receivers.

[0107] To summarize, the receiver 400 may comprise M primary combiners 603, 604, where each primary combiner of the M primary combiners 603, 604 is configured to combine analog baseband signals from a respective mixer of the M mixers 404, 405 from each branch of the N branches. The receiver 400 may further comprise M analog filters 605, 606, where each analog filter of the M analog filters 605, 606 is configured to filter a respective combined analog baseband signal from a respective primary combiner of the M primary combiners 603, 604 with respect to a respective baseband sub-band. The receiver 400 may further comprise a secondary combiner 607 configured to combine the filtered analog baseband signals. The receiver 400 may further comprise an ADC 608 configured to convert the combined signal from the secondary combiner to a digital baseband signal.

[0108] Figure 7 shows a third embodiment of processing the signals from each branch of the receiver. This embodiment may be called a “single ADC embodiment” since only a single ADC is required.

[0109] In the third embodiment, signal combination from different branches occurs in the analog domain prior to conversion to the digital domain. This embodiment requires N analog signal paths to be routed to the ADC. In particular, for each branch, the signal from each mixer is provided to a respective analog filter, which filters the signal with respect to one of the subband baseband signals. In particular, each analog filter filters a signal such that the filtered signal only comprises one of the sub-bands of the M sub-bands. For each branch, all M filtered signals are combined by a primary combiner into a (wideband) analog baseband signal. The respective combined signals provided from each primary combiner is provided to a secondary combiner. The combined signal provided by the secondary combiner is provided to an ADC.

[0110] Although M can be any integer larger than 1 , Figure 7 shows the case when M=2 for improved visibility.

[0111] The top of Figure 7 shows the combination of two signals path for a first branch of N branches. In particular, the signal from a first mixer of the first branch is provided to an analog filter 705, which filters the signal with respect to the sub-band BB1. In particular, the analog filter 705 may reject all frequencies other than those constituting the sub-band BB1. The signal path from the first mixer of the first branch into the analog filter 705 is denoted 701. Furthermore, the signal from a second mixer of the first branch is provided to an analog filter 706, which filters the signal with respect to the sub-band BB2. In particular, the analog filter 706 may reject all frequencies other than those constituting the sub-band BB2. The signal path from the second mixer into the analog filter 706 is denoted 702. The filtered signals provided by the analog filters 705, 706 are combined by a primary combiner 709. The output of the primary combiner 709 comprises a (wideband) analog baseband signal comprising both the sub-bands BB1 and BB2.

[0112] The bottom of Figure 7 shows the combination of two signals path for the Nth branch of N branches. In particular, the signal from a first mixer of the Nth branch is provided to an analog filter 707, which filters the signal with respect to the sub-band BB1. In particular, the analog filter 707 may reject all frequencies other than those constituting the sub-band BB1. The signal path from the first mixer of the Nth branch into the analog filter 707 is denoted 703. Furthermore, the signal from a second mixer of the Nth branch is provided to an analog filter 708, which filters the signal with respect to the sub-band BB2. In particular, the analog filter 708 may reject all frequencies other than those constituting the sub-band BB2. The signal path from the second mixer into the analog filter 708 is denoted 704. The filtered signals provided by the analog filters 707, 708 are combined by a primary combiner 710. The output of the primary combiner 710 comprises a (wideband) analog baseband signal comprising both the sub-bands BB1 and BB2.

[0113] The signals provided by each of the N primary combiners are combined by a secondary combiner 711. The combined signal from the secondary combiner 711 is provided to an ADC 712. The output of the ADC 712 is denoted 713 and comprises a (wideband) digital baseband signal comprising both the sub-bands BB1 and BB2. The signal at 713 thus comprises a baseband signal provided via an intended beam steering of the antenna array 210 with reduced beam squint as compared to prior art receivers.

[0114] To summarize, the receiver 400 may comprise M analog filters 701 :704 for each branch of the N branches. In each branch of the N branches, each analog filter of the M analog filters 701 , 702; 703, 704 is configured to filter a respective analog baseband signal from a respective mixer of the M mixers 404, 405 with respect to a respective baseband sub-band. The receiver 400 may further comprise N primary combiners 709, 710, where each primary combiner of the N primary combiners 709, 710 is configured to combine all filtered analog baseband signal of a respective branch. The receiver 400 may further comprise a secondary combiner 711 configured to combine the respective combined signals from the N primary combiners 709, 710. The receiver 400 may further comprise an ADC 712 configured to convert the combined signal from the secondary combiner 711 to a digital baseband signal.

[0115] Figure 8 shows a fourth embodiment of processing the signals from each branch of the receiver. This embodiment may be called an “M by N ADC embodiment” since M times N ADCs are required. Particularly, for each branch, one ADC per path is required. As mentioned, if the I and Q components are counted as 2 ADCs, there will be 2*M*N ADCs.

[0116] In the fourth embodiment, each branch is provided with M ADCs. M by N signals are filtered in the digital domain and thereafter combined. In particular, for each branch, the signal from each mixer is provided to a respective ADC. The respective signals from the respective ADCs are provided to respective digital filters, which filters the signal with respect to one of the subband baseband signals. In particular, a digital filter filters a signal such that the filtered signal only comprises one of the sub-bands of the M sub-bands. All M by N filtered signals are combined by a combiner into a (wideband) digital baseband signal.

[0117] Although M can be any integer larger than 1 , Figure 8 shows the case when M=2 for improved visibility. The top of Figure 8 shows two signals paths for a first branch of N branches. In particular, the signal from a first mixer of the first branch is provided to an ADC 809. The baseband path 805 represents the signal propagation path between the first mixer of the first branch and the ADC 809. The baseband path 805 may contain anti-alias filters and variable gain amplifiers. The input into the baseband path 805 is denoted 801. The digital signal provided by the ADC 809 is provided to a digital filter 813, which filters the signal with respect to the sub-band BB1. In particular, the digital filter 813 may reject all frequencies other than those constituting the sub-band BB1. Furthermore, the signal from a second mixer of the first branch is provided to an ADC 810. The baseband path 806 represents the signal propagation path between the second mixer of the first branch and the ADC 810. The baseband path 806 may contain antialias filters and variable gain amplifiers. The input into the baseband path 806 is denoted 802. The digital signal provided by the ADC 810 is provided to a digital filter 814, which filters the signal with respect to the sub-band BB2. In particular, the digital filter 814 may reject all frequencies other than those constituting the sub-band BB2.

[0118] The bottom of Figure 8 shows two signals path for the Nth branch of N branches. In particular, the signal from a first mixer of the Nth branch is provided to an ADC 811. The baseband path 807 represents the signal propagation path between the first mixer of the Nth branch and the ADC 811. The input into the baseband path 807 is denoted 803. The digital signal provided by the ADC 811 is provided to a digital filter 815, which filters the signal with respect to the sub-band BB1. In particular, the digital filter 815 may reject all frequencies other than those constituting the sub-band BB1. Furthermore, the signal from a second mixer of the Nth branch is provided to an ADC 812. The baseband path 808 represents the signal propagation path between the second mixer of the Nth branch and the ADC 812. The input into the baseband path 808 is denoted 804. The digital signal provided by the ADC 812 is provided to a digital filter 816, which filters the signal with respect to the sub-band BB2. In particular, the digital filter 816 may reject all frequencies other than those constituting the subband BB2.

[0119] All N by 2 filtered signals are combined by a combiner 817. The output of the combiner 817 is denoted 818 and comprises a (wideband) digital baseband signal comprising both the subbands BB1 and BB2. The signal at 818 comprises a baseband signal provided via an intended beam steering of the antenna array 210 with reduced beam squint as compared to prior art receivers.

[0120] To summarize, the receiver 400 may comprise M ADCs 809:812 for each branch of the N branches. In each branch of the N branches, each ADC of the M ADCs 809, 810; 811 , 812 is configured to convert a respective analog baseband signal from a respective mixer of the M mixers 404, 405 to a respective digital baseband signal. The receiver 400 may further comprise M digital filters 813:816 for each branch of the N branches. In each branch of the N branches, each digital filter of the M digital filters 813, 814; 815, 816 is configured to filter a digital baseband signal from a respective ADC 809, 810; 811 , 812 with respect to a respective baseband sub-band. The receiver 400 may further comprise a combiner 817 configured to combine the filtered digital baseband signal from each of the M digital filters 813:816 of each branch of the N branches.

[0121] When the beam is steered far from boresight (e.g. more than 50 degrees), it may be desired to configure each digital filter to highly attenuate all sub-bands but one (e.g., provide an attenuation of more than 20 dB). However, when the beam is steered close to boresight (e.g. more less than 10 degrees), it may be desired to configure each digital filter to attenuate all sub-bands but one less compared to the case when the beam is steered far from boresight. In other words, each digital filter of the M digital filters 813:816 may be configured to filter the respective digital baseband signal based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210.

[0122] Figure 9A shows a schematic example of an IQ mixer 901 that may be used as a mixer of the transmitter 300. It should be noted that other types of IQ mixers may also be used. In particular, the figure shows a Gilbert-cell-based IQ mixer with LO up-conversion for a single data stream (comprising the in-phase and the quadrature streams).

[0123] In Figure 9A, Outp and Outn are the positive and negative polarity, respectively, of a differential combined output signal. loutp and loutn are the positive and negative polarity, respectively, of the differential current for the I component.

[0124] Qoutp and Qoutn are the positive and negative polarity, respectively, of the differential current for the Q component.

[0125] BBlp and BBln are the positive and negative polarity, respectively, of the differential baseband I component.

[0126] BBQp and BBQn are the positive and negative polarity, respectively, of the differential baseband Q component.

[0127] LOlp and LOIn are the positive and negative polarity, respectively, of the differential Local Oscillator I component.

[0128] LOQp and LOQn are the positive and negative polarity, respectively, of the differential Local Oscillator Q component.

[0129] Figure 10 shows a generalized transmitter from Figure 3. As mentioned, Figure 3 shows a transmitter where M=2. Figure 10, on the other hand, shows the case where M is any integer larger than 1 . Although the transmitter 300 disclosed herein comprises two or more branches, Figure 10 only shows a single branch for improved visibility. The top path of Figure 10 (comprising the DAC 310, the baseband path 308, the mixer 304) is the same as in Figure 3. The bottom of Figure 10 shows the Nth path, comprising a DAC, a baseband path, and the Nth mixer 314. The output from all mixers of the transmitter 300 are provided to combiner 303. Note that the DACs and the baseband paths may be shared between different branches.

[0130] The IQ mixer 901 (for a single data stream) may be used for any one of the branches of Figure 10. If the mixer 304 is implemented as the IQ mixer 901 of Figure 9A, the output of the baseband path 308 provides BBlp / BBIn and BBQp / BBQn, the output of the variable phase shift unit 306 provides LOIp / LOIn and LOQp / LOQn, and the output of the mixer 304 (that is inputted to the combiner 303) comprises Outp and Outn.

[0131] Figure 9B shows a schematic example of an IQ mixer 902 that may be used in the transmitter 300. In particular, the figure shows a Gilbert-cell-based IQ mixer with LO up- conversion for combination of two data streams (comprising respective in-phase and quadrature streams), i.e. , M=2.

[0132] In Figure 9B, Outp and Outn are the positive and negative polarity, respectively, of the differential combined output signal. loutpi and loutm are the positive and negative polarity, respectively, of the differential current for the I component from a first subband of a branch.

[0133] Ioutp2 and Ioutn2 are the positive and negative polarity, respectively, of the differential current for the I component from a second subband branch of the branch.

[0134] Qoutpi and Qoutni are the positive and negative polarity, respectively, of the differential current for the Q component from the first subband of the branch.

[0135] Qoutp2 and Qoutn2 are the positive and negative polarity, respectively, of the differential current for the Q component from the second subband of the branch.

[0136] BBlpi and BBlm are the positive and negative polarity, respectively, of the differential baseband I component from the first subband of the branch.

[0137] BBIp2 and BBIn2 are the positive and negative polarity, respectively, of the differential baseband I component from the second subband of the branch.

[0138] BBQpi and BBQni are the positive and negative polarity, respectively, of the differential baseband Q component from the first subband of the branch.

[0139] BBQp2 and BBQn2 are the positive and negative polarity, respectively, of the differential baseband Q component from the second subband of the branch. LOIpi and LOIni are the positive and negative polarity, respectively, of the differential Local Oscillator I component from the first subband of the branch.

[0140] LOIp2 and LOIn2 are the positive and negative polarity, respectively, of the differential Local Oscillator I component from the second subband of the branch.

[0141] LOQpi and LOO is the positive and negative polarity, respectively, of the differential Local Oscillator Q component from the first subband of the branch.

[0142] LOQp2 and LOQn2 is the positive and negative polarity, respectively, of the differential Local Oscillator Q component from the second subband of the branch.

[0143] The improvement provided by the transmitter 300 and the receiver 400 depends on the size of the antenna array 210 and the angle of departure (AoD) or angle of arrival (AoA), i.e., intended beam direction. With larger sizes of the antenna array 210, and with larger angles from boresight, the more apparent the improvements of the present disclosure. The improvements are exemplified by Tables l-lll and Figures 11-12.

[0144] Table I shows the difference between prior art and the present disclosure for a 100 GHz carrier frequency, a 10-GHz bandwidth signal, an 8x1 antenna array (N=8), where M=2. The table shows a column for the AoD / AoA in degrees from boresight. For prior art case and for the transmitter 300 (or equivalently the receiver 400), the table shows an average loss across the 10-GHz bandwidth and the worst loss across the 10-GHz bandwidth. The loss is relative to a maximum beamforming gain across the band.

[0145] Table

[0146] Table II shows the difference between prior art and the present disclosure for a 100 GHz carrier frequency, a 10-GHz bandwidth signal, a 16x1 antenna array (N=16), where M=2. Table II shows the same parameters as Table I. Table

[0147] Table III shows the difference between prior art and the present disclosure for a 100 GHz carrier frequency, a 10-GHz bandwidth signal, a 32x1 antenna array (N=32), where M=2.

[0148] Table III shows the same parameters as Table I.

[0149] Table III

[0150] Figure 11 illustrates the gain of the transmitter 300 (or equivalently the receiver 400) versus frequency for a 100 GHz carrier frequency, 10-GHz bandwidth signal, a 32x1 antenna (N=32), where M=2, and a 60 degrees AoD (or AoA). In particular, the figure shows a difference between prior art (the dashed line) and present disclosure (solid line). As is seen, the beamforming gain degradation due to beam squint is lower for the transmitter 300 (or the receiver 400) compared to the prior art solution. The discontinuity at 100 GHz in Figure 11 , is due to difference in relative bandwidth when dividing the 10-GHz band into two equal portions of 5 GHz each. To avoid the discontinuity and minimize the overall beam-squint, the bandwidth separation should be moved from the center frequency of the channel to a slightly lower frequency. To make the relative bandwidths equal, the bandwidth separation should comply with these two equations. BW = BW±+ BW2

[0151] BW±BW2

[0152] ~ BW - BW±=e, BW - BW2fc - 2 - fc+- 2 - where BW is the bandwidth of the (wideband) baseband signal, BW±is the bandwidth of a first sub-band baseband signal, BW2is the bandwidth of a second sub-band baseband signal, and fcis the carrier frequency.

[0153] Figure 12 shows a similar gain curve as Figure 11 , but where the correction according to the two equations above has been used for the transmitter 300 (or the receiver 400). It can be noted that, compared to Figure 11 , the worst loss for the 32x1 antenna case is reduced from 1 .88 dB to 1 .79 dB for the present disclosure.

[0154] Due to implementations aspects and the small impact of the second order effect of equal bandwidth division, this may be ignored in some embodiments, and equal sized BWi and BW2 may be used.

[0155] The two equations above can be generalized to M sub-band baseband signals: where n indicates one of the M sub-band baseband signals and k indicates where the index of BW between 1 and M and indicates the bandwidth of the M sub-bands, so that BWi is the bandwidth of the first sub-band, BW2 the bandwidth of the second, and BWM the bandwidth of the last sub-band.

[0156] Figure 13 illustrates a method 1300 for enabling transmission of RF signals via an antenna array 210 comprising a plurality of antenna elements 211 :214. The transmitter 300 comprising N branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements 211 :214, where N is an integer larger than 1. The method 1300 may, e.g., be performed by the transmitter 300, discussed in connection to Figures 3 and 10, or by the transmitter 1500, discussed in more detail below in connection to Figure 15. Furthermore, the transmitter 300 of the method 1300 may be the transmitter 300, discussed in connection to Figures 3 and, or the transmitter 1500, discussed in more detail below in connection to Figure 15. The method 1300 comprises obtaining 1310, for each branch of the N branches, M analog sub-band baseband signals, where M is an integer larger than 1. Note that the M analog subband baseband signals may be equal in all N branches. In that way, it is possible to share parts like DACs and filters between the N branches.

[0157] The method 1300 further comprises upconverting 1320, for each branch of the N branches, each of the M analog sub-band baseband signals to respective sub-band RF signals with a difference in phase.

[0158] The method 1300 also comprises combining 1330, for each branch of the N branches, M sub-band RF signals to one of the respective RF signals.

[0159] The method 1300 may comprise transmitting 1340 the respective RF signals by respective antenna elements 211 :214.

[0160] In the method 1300, in each branch of the N branches, M analog sub-band baseband signals may comprise respective sub-bands of an analog baseband signal.

[0161] In the method 1300, in each branch of the N branches, M analog sub-band baseband signals may comprise respective frequency-adjacent sub-bands of the analog baseband signal.

[0162] The upconverting 1320 may comprise mixing 1321 each of the M analog sub-band baseband signals with a respective LO signal, wherein each of the respective LO signals is associated with a carrier frequency and a difference in phase.

[0163] The difference in phase may be configured based on beam directions of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array 210.

[0164] Figure 14 illustrates a method 1400 for enabling reception of RF signals via an antenna array 210 comprising a plurality of antenna elements 211 :214. The receiver 400 comprises N branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements 211 :214, where N is an integer larger than 1 . The method 1400 may, e.g., be performed by the receiver 400, discussed in connection to Figures 4-8, or by the receiver 1600, discussed in more detail below in connection to Figure 16. Furthermore, the receiver 400 of the method 1400 may be the receiver 400, discussed in connection to Figures 4-8, or the receiver 1600, discussed in more detail below in connection to Figure 16.

[0165] The method 1400 comprises obtaining 1420, for each branch of the N branches, a respective RF signal.

[0166] The method 1400 further comprises splitting 1430, for each branch of the N branches, the obtained RF signal to M RF signals, where M is an integer larger than 1.

[0167] The method 1400 also comprises downconverting 1440, for each branch of the N branches, each of the M RF signals to respective analog baseband signals with a difference in phase. The method 1400 may comprise receiving 1410 the respective RF signals by respective antenna elements 211 :214.

[0168] In the method 1400, for each branch of the N branches, each of the M analog baseband signals may comprise M analog sub-band baseband signals.

[0169] In the method 1400, the M analog sub-band baseband signals may be respective frequency-adjacent sub-bands.

[0170] The downconverting 1440 may comprise mixing 1441 a respective RF signal of the M RF signals with a respective LO signal, where each of the respective LO signals is associated with a carrier frequency and a difference in phase.

[0171] The difference in phase may be configured based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210.

[0172] In a first example, the method 1400 comprises combining 1451 analog baseband signals from a respective mixer of the M mixers 404, 405 from each branch of the N branches; converting 1452 respective combined analog baseband to a respective digital baseband signal; filtering 1453 a respective digital baseband signal with respect to a respective baseband sub-band; and combining 1454 the filtered digital baseband signals.

[0173] In the first example, the filtering may comprise filtering 1455 the respective digital baseband signals based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210.

[0174] In a second example, the method 1400 comprises combining 1461 analog baseband signals from a respective mixer of the M mixers 404, 405 from each branch of the N branches; filtering 1462 respective combined analog baseband signals with respect to a respective baseband sub-band; combining 1463 the filtered analog baseband signals; and converting 1464 the combined filtered analog baseband signals to a digital baseband signal.

[0175] In a third example, the method 1400 comprises, for each branch of the N branches, filtering 1471 a respective analog baseband signal with respect to a respective baseband sub-band; for each branch of the N branches, combining 1472 all filtered analog baseband signals; combing 1473 all combined filtered analog baseband signals; and converting 1474 the signal from the latter combination to a digital baseband signal.

[0176] In a fourth example, the method 1400 comprises, for each branch of the N branches, converting 1481 respective analog baseband signals respective digital baseband signals; for each branch of the N branches, filtering 1482 respective digital baseband signals with respect to respective baseband sub-bands; and combining 1483 the filtered digital baseband signals.

[0177] In the fourth example, the filtering may comprise filtering 1484 respective digital baseband signals based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array 210. Figure 15 shows a schematic block diagram of embodiments of a transmitter 1500. Although not shown in Figure 15, the transmitter 1500 may comprise known conventional features for such devices, such as a power source like a battery or mains connection. Furthermore, transmitter 1500 may comprise all features of the transmitter 300, as discussed above in connection to Figures 3 and 10.

[0178] The transmitter 1500 may comprise processing circuitry 1510 and a memory 1520. The processing circuitry 1510 may comprise a receiving module 1511 and a transmitting module 1512. The receiving module 1511 and the transmitting module 1512 may comprise radio frequency circuitry and baseband processing circuitry capable of transmitting and receiving a radio signal in the wireless communications network 100. The receiving module 1511 and the transmitting module 1512 may also form part of a single transceiver. The transmitter 1500 may comprise additional components, such as, an obtaining module 1513, a frequency conversion module 1514, and / or a combining module 1515, responsible for providing functionality to support the embodiments of the transmitter 1500.

[0179] The transmitter 1500 may be configured to execute the method 1300 discussed above. It should also be noted that some or all of the functionality being performed by the transmitter 1500 may be provided by the processing circuitry 1510 (or any of the obtaining module 1513, the frequency conversion module 1514, and / or the combining module 1515) executing instructions stored on a computer-readable medium, such as, e.g. the memory 1520 shown in Figure 15.

[0180] The method 1500 may be implemented through one or more processors, such as the processing circuitry 1510 in the transmitter 1500 depicted in Figure 15, together with computer program code for performing the functions and actions of the embodiments herein. The program code may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code or code means for performing the embodiments herein when being loaded into the processing circuitry 1510 in the transmitter 1500. The computer program code may e.g. be provided as pure program code in the transmitter 1500 or on a server and downloaded to the transmitter 1500. Thus, it should be noted that the modules of the transmitter 1500 may in some embodiments be implemented as computer programs stored in memory, e.g. in the memory 1520 in Figure 15, for execution by processors or processing modules, e.g. the processing circuitry 1510 of Figure 15. Those skilled in the art will also appreciate that the processing circuitry 1510 and the memory 1520 described above may refer to a combination of analog and digital circuits, and / or one or more processors configured with software and / or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processing circuitry 1510 perform as described above. In an example, the transmitting module 1512 and / or the obtaining module 1513 may comprise one or more DACs (such as 310, 311). In another example, the transmitting module 1512 and / or the frequency conversion module 1514 may comprise one or more mixers (such as 304, 305, 314). In another example, the transmitting module 1512 and / or the combining module 1515 may comprise one or more combiners (such as 303). In another example, the transmitting module 1512 may comprise one or more antenna elements (such as 211 :214). One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

[0181] Figure 16 shows a schematic block diagram of embodiments of a receiver 1600. Although not shown in Figure 16, the receiver 1600 may comprise known conventional features for such devices, such as a power source like a battery or mains connection. Furthermore, receiver 1600 may comprise all features of the receiver 400, as discussed above in connection to Figures 4-8.

[0182] The receiver 1600 may comprise processing circuitry 1610 and a memory 1620. The processing circuitry 1610 may comprise a receiving module 1611 and a transmitting module 1612. The receiving module 1611 and the transmitting module 1612 may comprise radio frequency circuitry and baseband processing circuitry capable of transmitting and receiving a radio signal in the wireless communications network 100. The receiving module 1611 and the transmitting module 1612 may also form part of a single transceiver. The transmitter 1600 may comprise additional components, such as, an obtaining module 1613, a splitting module 1614, and / or a frequency conversion module 1615, responsible for providing functionality to support the embodiments of the receiver 1600.

[0183] The receiver 1600 may be configured to execute the method 1400 discussed above. It should also be noted that some or all of the functionality being performed by the receiver 1600 may be provided by the processing circuitry 1610 (or any of the obtaining module 1613, the splitting module 1614, and / or the frequency conversion module 1615) executing instructions stored on a computer-readable medium, such as, e.g. the memory 1620 shown in Figure 16.

[0184] The method 1600 may be implemented through one or more processors, such as the processing circuitry 1610 in the receiver 1600 depicted in Figure 16, together with computer program code for performing the functions and actions of the embodiments herein. The program code may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code or code means for performing the embodiments herein when being loaded into the processing circuitry 1610 in the receiver 1600. The computer program code may e.g. be provided as pure program code in the receiver 1600 or on a server and downloaded to the receiver 1600. Thus, it should be noted that the modules of the receiver 1600 may in some embodiments be implemented as computer programs stored in memory, e.g. in the memory 1620 in Figure 16, for execution by processors or processing modules, e.g. the processing circuitry 1610 of Figure 16. Those skilled in the art will also appreciate that the processing circuitry 1610 and the memory 1620 described above may refer to a combination of analog and digital circuits, and / or one or more processors configured with software and / or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processing circuitry 1610 perform as described above. In an example, the receiving module 1611 and / or the obtaining module 1613 may comprise one or more antenna elements (such as 211 :214). In another example, the receiving module 1611 and / or the splitting module 1614 may comprise one or more splitters (such as 403). In another example, the receiving module 1611 and / or the frequency conversion module 1615 may comprise one or more mixers (such as 404, 405). One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

[0185] The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other.

[0186] It should be noted that the word “comprising” does not necessarily exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware.

[0187] It should also be noted that the various example embodiments described herein are described in the general context of method steps or processes, which may be implemented in one aspect by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may include removable and nonremovable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

[0188] The embodiments herein are not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be construed as limiting.

Claims

CLAIMS1. A transmitter (300) for transmitting radio frequency, RF, signals via an antenna array (210) comprising a plurality of antenna elements (211:214), the transmitter (300) comprisingN branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements (211 :214), where N is an integer larger than 1 , wherein each branch of the N branches comprises M mixers (304, 305, 314), where M is an integer larger than 1 , wherein, in each branch of the N branches, each mixer of the M mixers (304, 305, 314) is configured to receive a respective analog sub-band baseband signal and upconvert said respective analog sub-band baseband signal to a respective sub-band RF signal, wherein, in each branch of the N branches, the M mixers (304, 305, 314) are configured to introduce a difference in phase between each of the M sub-band RF signals, wherein each branch of the N branches comprises a respective combiner (303) configured to combine M sub-band RF signals of that branch to one of the respective RF signals.

2. The transmitter (300) according to claim 1 , wherein, in each branch of the N branches, M analog sub-band baseband signals comprise respective sub-bands of an analog baseband signal.

3. The transmitter (300) according to any previous claim, wherein, in each branch of the N branches, M analog sub-band baseband signals comprise respective frequency-adjacent sub-bands of the analog baseband signal.

4. The transmitter (300) according to any previous claim, wherein, in each branch of the N branches, each mixer of the M mixers (304, 305, 314) is configured to mix a respective received analog sub-band baseband signal with a respective local oscillator, LO, signal, wherein each of the respective LO signals is associated with a carrier frequency and a difference in phase.

5. The transmitter (300) according to claim 4, wherein, in each branch of the N branches, the difference in phase is configured based on beam directions of the sub-band RF signals as comprised in the RF signals to be transmitted by the antenna array (210).

6. The transmitter according to any previous claim, wherein, in each branch of the N branches, each mixer of the M mixers (304, 305, 314) comprise a respective in-phase and quadrature, IQ, mixer.

7. The transmitter (300) according to any previous claim, comprising respective digital-to- analog converters, DACs, (310, 311) arranged to convert respective digital sub-band baseband signals to the M analog sub-band baseband signals.

8. A transmitter system comprising the transmitter (300) according to any of claims 1-7 and the antenna array (210).

9. A receiver (400) for receiving radio frequency, RF, signals via an antenna array (210) comprising a plurality of antenna elements (211 :214), the receiver (400) comprisingN branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements (211 :214) , where N is an integer larger than 1 , wherein each branch of the N branches comprises M mixers (404, 405), where M is an integer larger than 1 , wherein each branch of the N branches comprises a respective splitter (403) configured to split the RF signal received by that branch to the M mixers (404, 405) of that branch, wherein, in each branch of the N branches, each mixer of the M mixers (404, 405) is configured to receive the RF signal received by the corresponding branch and downconvert said RF signal to an analog baseband signal, wherein, in each branch of the N branches, the M mixers (404, 405) are configured to introduce a difference in phase between each of the analog baseband signals.

10. The receiver (400) according to claim 9, wherein, for each branch of the N branches, each of the M analog baseband signals comprise M analog sub-band baseband signals.

11. The receiver (400) according to claim 10, wherein the M analog sub-band baseband signals are respective frequency-adjacent sub-bands.

12. The receiver (400) according to any of claims 9-11 , wherein, in each branch of the N branches, each mixer of the M mixers (404, 405) is configured to mix a respective received RF signal with a respective local oscillator, LO, signal, wherein each of the respective LO signals is associated with a carrier frequency and a difference in phase.

13. The receiver (400) according to claim 12, wherein, in each branch of the N branches, the difference in phase is configured based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array (210).

14. The receiver (400) according to any of claims 9-13, wherein, in each branch of the N branches, each mixers of the M mixers (404, 405) comprises a respective in-phase and quadrature, IQ, mixer.

15. The receiver (400) according to any of claims 9-14, comprising:M primary combiners (503, 504), wherein each primary combiner of the M primary combiners (503, 504) is configured to combine analog baseband signals from a respective mixers of the M mixers (404, 405) from each branch of the N branches;M analog-to-digital converters, ADCs, (505, 506) wherein each ADC of the M ADCs (505, 506) is configured to convert a respective combined analog baseband signal from a respective primary combiner of the M primary combiners (503, 504) to a respective digital baseband signal;M digital filters (507, 508), wherein each digital filter of the M digital filters (507, 508) is configured to filter a respective digital baseband signal with respect to a respective baseband sub-band; and a secondary combiner (509) configured to combine the filtered digital baseband signals.

16. The receiver (400) according to claim 15, wherein each digital filter of the M digital filters (507, 508) is configured to filter the respective digital baseband signal based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array (210).

17. The receiver (400) according to any of claims 9-14, comprising:M primary combiners (603, 604), wherein each primary combiner of the M primary combiners (603, 604) is configured to combine analog baseband signals from a respective mixer of the M mixers (404, 405) from each branch of the N branches;M analog filters (605, 606), wherein each analog filter of the M analog filters (605, 606) is configured to filter a respective combined analog baseband signal from a respective primary combiner of the M primary combiners (603, 604) with respect to a respective baseband subband; and a secondary combiner (607) configured to combine the filtered analog baseband signals; an analog-to-digital converter, ADC, (608) configured to convert the combined signal from the secondary combiner to a digital baseband signal.

18. The receiver (400) according to any of claims 9-14, comprising:M analog filters (701 :704) for each branch of the N branches, wherein, in each branch of the N branches, each analog filter of the M analog filters (701 , 702; 703, 704) is configured to filter a respective analog baseband signal from a respective mixer of the M mixers (404, 405) with respect to a respective baseband sub-band;N primary combiners (709, 710), wherein each primary combiner of the N primary combiners (709, 710) is configured to combine all filtered analog baseband signal of a respective branch; a secondary combiner (711) configured to combine the respective combined signals from the N primary combiners (709, 710); and an analog-to-digital converter, ADC, (712) configured to convert the combined signal from the secondary combiner (711) to a digital baseband signal.

19. The receiver (400) according to any of claims 9-14, comprising:M analog-to-digital converters, ADCs, (809:812) for each branch of the N branches, wherein, in each branch of the N branches, each ADC of the M ADCs (809, 810; 811 , 812) is configured to convert a respective analog baseband signal from a respective mixers of the M mixers (404, 405) to a respective digital baseband signal;M digital filters (813:816) for each branch of the N branches, wherein, in each branch of the N branches, each digital filter of the M digital filters (813, 814; 815, 816) is configured to filter a digital baseband signal from a respective ADC (809, 810; 811 , 812) with respect to a respective baseband sub-band; a combiner (817) configured to combine the filtered digital baseband signal from each of the M digital filters (813:816) of each branch of the N branches.

20. The receiver (400) according to claim 21 , wherein each digital filter of the M digital filters (813:816) is configured to filter the respective digital baseband signal based on beam directions of sub-band RF signals as comprised in the RF signals to be received by the antenna array (210).

21. A receiver system comprising the receiver (400) according to any of claims 9-20 and the antenna array (210).

22. A communication apparatus comprising the transmitter (300) according to any of claims 1-7, the transmitter system according to claim 8, the receiver (400) according to any of claims 9-20, and / or the receiver system according to claim 21 .

23. The communication apparatus according to claim 22, the communication apparatus being a wireless communications device (121) for a wireless communications network (100).

24. The communication apparatus according to claim 22, the communication apparatus being a network node (110) for a wireless communications network (100).

25. A method (1300), by a transmitter (300, 1500), for enabling transmission of radio frequency, RF, signals via an antenna array (210) comprising a plurality of antenna elements (211 :214), the transmitter (300, 1500) comprising N branches for providing respective RF signals to respective antenna elements of the plurality of antenna elements (211 :214), where N is an integer larger than 1 , the method (1300) comprising: obtaining (1310), for each branch of the N branches, M analog sub-band baseband signals, where M is an integer larger than 1 , upconverting (1320), for each branch of the N branches, each of the M analog sub-band baseband signals to respective sub-band RF signals with a difference in phase, combining (1330), for each branch of the N branches, M sub-band RF signals to one of the respective RF signals.

26. A method (1400), by a receiver (400, 1600), for enabling reception of radio frequency, RF, signals via an antenna array (210) comprising a plurality of antenna elements (211 :214) , the receiver (400, 1600) comprising N branches configured to receive respective RF signals from respective antenna elements of the plurality of antenna elements (211 :214), where N is an integer larger than 1 , the method (1400) comprising obtaining (1420), for each branch of the N branches, a respective RF signal,splitting (1430), for each branch of the N branches, the obtained RF signal to M RF signals, where M is an integer larger than 1 , downconverting (1440), for each branch of the N branches, each of the M RF signals to respective analog baseband signals with a difference in phase.

Images