Digital predistortion in distributed amplifier antenna array

Abstract

Global digital predistortion techniques for distributed amplifier antenna array. An RF distribution network splits a low-power RF signal into multiple RF signals. A set of amplifiers resides within an antenna array column and each amplifier produces a respective amplified signal with a substantially equal power level. A first amplifier is connected to and positioned substantially adjacent to a nominal subarray of one or more radiating elements. A second amplifier is connected to and positioned substantially adjacent to a tapering subarray having more radiating elements than the nominal subarray. First and second observation couplers and an observation signal aggregator generate an aggregated observation signal. A DPD module updates a DPD parameter based on the aggregated observation signal.

Description

DIGITAL PREDISTORTION IN DISTRIBUTED AMPLIFIER ANTENNA ARRAYDESCRIPTION

[0001] The present application is a non-provisional filing of, and claims benefit under 35 U.S.C. § 119(e) from, U.S. Provisional Patent Application Ser. No. 63 / 563,136, filed Mar. 8, 2024. The contents of that application are incorporated herein by reference in their entirety.BACKGROUND

[0002] The present disclosure relates to the field of telecommunications, and more specifically to a distribution of signals for transmission over antenna radiating elements. It may find applications in the field of wireless communications such as 2G / 3G / 4G, LTE, LTE Advanced, and 5G, and the like.

[0003] In wireless base stations, a radio head (also known as a remote radio head or RRH) is a component that is responsible for the radio frequency (RF) transmission and reception functions. The radio head is typically located at the top of a cell tower or distributed throughout a network of small cells, and it plays a key role in the deployment of modem cellular networks. A typical RRH may include 10 Watt amplifiers for generating a high-power RF signal that is then distributed over a coaxial feed network to divide the amplified power amongst a set of antenna elements. The coaxial feed network may also adjust the phase of the divided high- power amplified signals.

[0004] This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present disclosure that are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the systems and methods described herein. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.SUMMARY

[0005] Described herein are wireless radio transmission and reception systems using antenna arrays having one or more distributed amplifier radio frequency (RF) transceiver chains. Amplifying RF signals closer to the radiating elements of an antenna array not only increases the energy efficiency by eliminating signal loss associated with splitting and beamforming of high-power analog RF signals, but in combination with more cost efficient transmit filter structures and easy-to-manufacture modular assemblies provides for more readily adaptablesystem configurations, thereby providing opportunities for adaptable system deployments, making the overall radio signal transmission system more efficient and robust.

[0006] Each distributed amplifier RF transceiver chain is configured to accept a transmit RF signal source, such as a modulated RF signal from an RF integrated circuit (RFIC), that is provided to a low-power RF transmit distribution network for providing the analog RF signal to a plurality of RF power amplifiers distributed throughout the antenna array. The RF power amplifiers, in turn, are distributed such that they positioned along a column of radiating elements such that they are substantially adjacent to their associated radiating antenna elements. The transceiver chain of each array also includes receive RF front end components, such as distributed low noise amplifiers, each connected to a respective antenna element and configured to receive an RF signal, amplify it, and provide it to an RF receive combiner network.

[0007] The low-power RF transmit distribution network includes a signal splitter to divide signal power from a given input RF signal source to a number of RF outputs (e.g., at least two such outputs, with some embodiments having 5, 7, or 8 or more identical RF outputs) that are used to drive the individual distributed RF power amplifier stages. The low power RF distribution network may also include a beamforming network to adjust the phase of the signals being fed to each power amplifier such that the RF signals transmitted from each element create a focused and directional beam, and which may be used to implement an electronic beam tilt. Some embodiments of the RF distribution network may include a buffer amplifier or pre-amplifier prior to signal splitting. The inclusion of a buffer amplifier may depend upon the power level of the input RF signal received from the RFIC or other modulated RF signal source.

[0008] Each of the distributed RF power amplifiers may take the form of a balanced amplifier, a Doherty amplifier, a feedforward noise cancelling amplifier, an outphasing amplifier, or another suitable amplifier structure(s). Amplification of the individually distributed RF signals substantially reduces signal loss that is otherwise associated with distributing a high-power RF signal from an RF power amplifier through a high-power distribution network such as signal dividers, phase shifters, and associated RF cabling. Each such distributed RF amplifier also includes an output RF bandpass filter to reduce out of band distortion. In some embodiments, the transmit filter structure includes a set of cross-coupled ceramic resonators placed within an enclosure. Each of the distributed RF power amplifiers operates at a common power level. This ensures that distortions introduced at each amplifierare more similar as compared to distortions introduced by like RF power amplifiers operating at different power levels.

[0009] The arrays may take the form of a linear array (aligned vertically or horizontally), generally referred to herein as a “column” of antenna elements, or radiating elements, where each element is driven by a separate distributed power amplifier, which is fed by a respective output of the low power RF distribution network. In some embodiments the radiating elements for two such transceiver chains are associated with sets of cross-polarized radiating elements having an orthogonal orientation (commonly referred to as vertical and horizontal polarizations, or equivalently, as ±45° polarizations), so that a single column within an array comprises two physically overlapping sets of elements, with each set being driven by a separate analog RF signal distributed through its associated low power RF distribution network. Some embodiments may also be configured to have at least some of the distributed RF power amplifiers drive a group of parallel-connected radiating elements, which form a subarray of antenna elements. In some embodiments, the radiating elements may be used for both transmission and reception, such as in a time-domain duplexing (TDD) system, or they may use separate radiating elements in a frequency division duplexing (FDD) system.

[0010] Associated with the transmit low power RF distribution network is an RF transmit observation network configured to obtain and combine observation samples of the outputs of each of the distributed RF amplifiers. The observation samples are obtained from RF signal couplers connected to the outputs of the distributed RF power amplifiers, phase-adjusted to remove phase off sets imposed by the transmit RF distribution network, and combined into a single analog RF observation signal to be fed to an observation receiver within the RF transceiver, such as an RFIC. The observation receiver may then be used to compare the aggregated amplifier output signal samples with the intended transmit signal and perform global digital predistortion (DPD) signal processing on the original transmit RF signal. The RF power amplifiers operate at a common power level, ensuring that the aggregated amplifier output signal samples more closely resemble each individual amplifier observation sample.

[0011] In some embodiments, the overall systems described herein may be assembled from modularized subassemblies, including modularized RF subassemblies comprising distributed RF power amplifiers (each having an associated distributed RF transmit filter subassembly), and having a predetermined number of transmit / receive signal paths (such as two crosspolarized transmit and receive RF signals, referred to herein as 2T2R), or multiple frequency bands (referred to herein as dual-band 2T2R) and being preconfigured according to either aTDD or FDD operational architecture. Each RF subassembly may be configured with a desired arrangement of antenna radiating elements or radiating element subarrays of various dimensions. The modularized RF assemblies may then be configured according to the desired array dimension, the number of desired RF power amplifiers, and of the overall desired power, and connected to respective RF signal sources and receivers through associated properly-dimensioned transmit low-power distribution networks, RF transmit observation networks, and RF receive combiner networks.

[0012] Note that the modular aspects of the RF front end architectures described herein may be combined in various ways to achieve higher-dimensional beamforming. That is, a larger array may be formed by combining two or more sets of distributed amplifier RF front end systems in each array column of a multiple column array. For example, a single array column may comprise two separate 2T2R distributed amplifier RF systems to create a 4T4R column. This modularity provides for higher-dimensional digital beamforming in combination with RF analog beam forming (i.e., hybrid beamforming), and including improved electronic tilt. Such systems retain the characteristics of having sets of separate power amplifiers being fed by a low-power RF distribution network for each RF signal path, as well as an associated observation network used for global DPD correction within each such RF chain.BRIEF DESCRIPTION OF THE FIGURES

[0013] Fig. 1 depicts a block diagram of a 2T2R distributed amplifier column array driven by a 2T2R transceiver RFIC;

[0014] Fig. 2 depicts one instance of a distributed amplifier RF front end;

[0015] Fig. 3 depicts a block diagram of a TDD 2T2R distributed amplifier column array driven by a 2T2R transceiver RFIC;

[0016] Fig. 4 depicts an RF transmit observation network associated with the transmit low power RF distribution network;

[0017] Fig. 5 depicts the linearity of a single RF power amplifier used in the distributed amplifier RF transceiver chains and a combined linearity of the set of distributed amplifiers;

[0018] Fig. 6 depicts a block diagram of a FDD 2T2R distributed amplifier column array driven by a 2T2R transceiver RFIC;

[0019] Fig. 7 depicts additional details of the transmit signal circuits of a dual band 2T2R distributed amplifier column array;

[0020] Fig. 8 depicts additional details of the receive signal circuits of a dual band 2T2R distributed amplifier column array;

[0021] Fig. 9 depicts two columns of an FDD dual band 2T2R (combined to create a dual band 4T4R having a total of 8T8R transceiver chains) distributed amplifier column array;

[0022] Fig. 10 depicts embodiments of arrays of various sizes;

[0023] Fig. 11 depicts aspects of a single cavity resonator;

[0024] Fig. 12 depicts aspects of a single ceramic TEOld resonator;

[0025] Fig. 13 depicts a filter assembly suitable for use by each distributed amplifier module of a 2T2R array, having two multi-stage cross-coupled resonator TX filters and two crosscoupled resonator RX filters;

[0026] Fig. 14 depicts a filter assembly suitable for use by each distributed amplifier module of a 2T2R array, having two cross-coupled resonator TX filters;

[0027] Fig. 15 depicts aspects of a modularized RF subassembly;

[0028] Fig. 16 depicts a block diagram of an embodiment described herein;

[0029] Fig. 17 depicts a low-power RF distribution network, an RF distributed antenna array, and a digital predistortion module; and,

[0030] Fig. 18 depicts a method for updating a digital predistortion module parameter.DETAILED DESCRIPTION

[0031] With respect to Fig. 1, a 2T2R TDD distributed amplifier column array 100 driven by a 2T2R transceiver RFIC 130 will be described, while Fig. 2 shows further details of each 1T1R RF TRX module 200, where each RF TRX element (e.g., each of 122, 129, etc.), contain two such modules 200. Antenna radiating elements 102, 104, 106, 108, 110, 112, 114, 116 are shown configured in a vertical column of cross polarized elements for transmitting two separate RF signals, referred to herein interchangeably as ±45° polarizations and vertical / horizontal (V / H) polarizations. Note that in the particular embodiment of Fig. 1, the top elements 102, 104 and bottom elements 114, 116, each form parallel connected radiating elements (e.g., line 118 carrying V / H RF signals) thereby forming respective subarrays driven by a set of RF power amplifiers, whereas the remaining cross-polarized elements are pairs of single elements (connected, e.g., by line 120 also providing V / H RF connections), each driven by a respective RF power amplifier.

[0032] Array configurations with radiating element subarrays positioned at the upper and / or lower edges of the array may advantageously be used to implement array signal power tapering to reduce sidelobe gratings. The parallel-connected elements may have a 50 / 50% power splitting or may be configured with a 60 / 40% power split (with 40% power provided to elements located at the furthest point of the column (i.e., extreme top and bottom elements). Microstrip transmissions lines, or other equivalent structures, may provide desired power splitting ratios.

[0033] The transmit (DL) and receive (UL) RF signals are split, and combined, respectively, in the low-power RF distribution network 126. The four RF signals (two transmit and two receive) are carried over lines 128 between the RFIC 130 and the RF distribution network 126. The distribution network 126 includes (i) a low-power RF transmit distribution network configured to distribute transmit RF signals (e.g., two such transmit signals 202 in a 2T2R configuration) to each of the respective RF power amplifiers 204 / 206 within the RF TRX elements 122, 129, etc., (ii) an RF transmit observation network configured to obtain RF observation signals from the various observation couplers 208, etc., within the RF TRX circuits and combine them into one or more aggregated RF transmit observation signals (e.g., two such observation signals in a 2T2R configuration, also carried over RF connection lines 128 back to observation receivers within the RFIC 130), and, in FDD configurations, (iii) separate RF receive combiner networks configured to combine receive RF signals from outputs 214 (that is, in TDD operations, the low-power RF transmit distribution network may also be configured to operate bi-directionally to also combine received RF signals). As will be described more fully below, each of the three distribution networks (RF transmit, RF transmit observation, and RF receive combiner) include respective sets of phase adjustment circuits to adjust the relative phase of each RF signal in the three distribution networks.

[0034] In some embodiments, the low-power RF transmit distribution network may also include a buffer amplifier (not shown) at the input 128 for each transmit signal source to provide sufficient signal to noise ratios (SNRs) of the transmit signals at the outputs of the RF distribution network 126.

[0035] Further with respect to the embodiment of Fig. 2, the distributed RF transmit signal is received at input 202 and is amplified by two stage LD MOS Doherty amplifier 204, 206, whose output is fed to circulator 210, which provides isolation and protection to the amplifier stage 206. The amplified RF signal is then provided to transmit filter 212 to remove out of band distortion components, and filtered signal is then provided to an antenna radiatingelement(s) over line 224. Uplink received RF signals are obtained from the antenna elements over line 224, processed by receive filter 222, and provide it to LNA 218 and our output on line 214. The LNA 218 may be bypassed using RF switches 216, 220.

[0036] With respect to Fig. 3, further details of an embodiment of a TDD 2T2R distributed amplifier column array driven by a 2T2R transceiver RFIC will be described. The RF IC 346 provides two downlink transmit signals on lines 344 to respective transmit-receive (T / R) switches 334, 336. In the downlink, the transmit signals are split within the distribution network 332 and provided to transceiver modules such as RF front end circuits 306, 348, etc. which in turn drive a cross polarized pair of radiating elements (or parallel-connected radiating element subarrays) from respective filtered outputs (e.g., lines 302, 304). In the embodiment of Fig. 3, the phase rotator circuits 320, 330 are shown contained within the RF front end circuit 306, but for purposes of this description, they may alternatively be considered to be part of RF distribution network 332. In some embodiments the RF distribution network elements, including the phase shifters and the phase shifter controllers, are all located on a single board within the system to eliminate the need for distributing phase shifter control signals to the individual distributed RF front end modules. For uplink signals received from the RF distribution networks 332 the phase is adjusted by phase rotators 330, 328 and provided by respective T / R switches 324, 326 to the respective power amplifiers 320, 322. An additional pair of T / R switches 312, 314 route the amplified signals through respective filters 308, 310.

[0037] In the TDD embodiment shown in Fig. 3, the filters 308, 310 are also used to process received signals which are routed by switches 312, 314 to LA circuits 316, 3 / 18, and are then routed to the phase shifters 328, 330 via switches 324, 326.

[0038] In some embodiments, the phase shifters 328, 330 each comprise a set of selectable delay lines of varying length to provide an associated phase delay of the RF signal. It should be noted that because the RF signal phase shifting is being performed on low-power RF signals, a less expensive phase shifter circuit may be used. So-called “handset grade” phase shifters may be used, and may take the form of a set of selectable microstrip transmission paths of varying lengths, rather than more elaborate high-power phase shifters. In particular, phase shifter circuits for high power signals involve considerations and features that ensure the circuit can handle the increased power levels without degradation, distortion, or damage. The components in a high power phase shifter circuit, such as resistors, capacitors, and inductors, need to be selected or designed to handle the increased power levels withoutoverheating or breaking down. Higher power components often have higher power ratings and are built to withstand greater thermal stresses. The materials used in the construction of circuit components should be chosen for their high electrical and thermal conductivity. The phase shifter circuits for high power applications should also have low insertion losses to minimize power dissipation within the circuit. Furthermore, increased electromagnetic isolation between the input and output ports of the phase shifter is required at higher power levels to avoid issues such as intermodulation distortion. The control mechanisms such as varactor diodes or other tunable components must also be capable of handling the power levels encountered in high power applications. Such designs constraints impose significant additional expense to the phase shifter circuits (i.e., phase adjustment circuits, phase shifters, phase adjusters, and the like).

[0039] In one embodiment, each of the phase adjustment circuits are controlled by a 4-bit control signal to select one of 16 possible delays. Such embodiments can be adjusted during a calibration procedure to remove any relative phase shifts associated with the respective distribution network itself. Such a calibration may be performed once during the manufacturing process or the calibration may be repeated after deployment of the system. The desired calibration phase offsets may be stored in the controller memory. Furthermore, the phase adjustment circuits may be configured to impose additional phase offsets to the respective distributed RF signals, depending on the physical location of the radiating elements within a given column, as well as a desired electronic beam tilt. One such embodiment provides seven discrete down tilt positions. More or fewer tilt settings may be configured according to the number of selectable delay paths, and the magnitude of their respective differential delays, in each phase adjustment circuit.

[0040] Fig. 4 shows a portion of a distributed amplifier radio frequency (RF) transceiver chain 400. The transceiver RFIC 402 shows a downlink transmit RF signal output on line 404 that is provided to an N-way power splitter 408. The outputs of the power splitter 408 are provided to respective 4-bit switched phase adjustment circuits (e.g., 412), the outputs of which are provided to the distributed RF power amplifiers (e.g., 414). In the RF transmit observation network, the outputs of each of the amplifiers are sampled using RF couplers (e.g., 416), and the sampled RF observation signals from the N amplifier paths are processed by additional 4 bit switched delay phase adjustment circuits (e.g., 420), before being combined in the N-way power combiner 410 to form an aggregated observation RF signal(i.e., aggregated RF observation signal, aggregated signal, combined RF observation signal, and the like) that is provided to the observation receiver of the RF IC 402 via line 406.

[0041] The RF IC 402 can provide digital predistortion (DPD) of the transmit signal 404 based on the measured characteristics of the aggregated RF transmit observation signal received on line 406. The results of the DPD signal processing are shown in Fig. 5, where signal plot 500 shows the raw linearity signal power 502 of a single RF power amplifier in the absence of DPD signal processing. Notably, the side lobe distortion is approximately 30 dB below the signal peak. Graph 550 shows overlaid plots of an amplifier output 504 from first amplifier (Dev 1) generated by a digitally pre-distorted input signal, an amplifier output 506 from a second amplifier (Dev 2) based on a digitally pre-distorted input signal, and a combined power spectrum of the combined amplifier outputs generated from pre-distorted input signals based on DPD algorithm operating on an aggregated RF transmit observation signal, also referred to herein as “global-DPD”. Notably, the out-of-band distortion associated with the combined RF power amplifiers is approximately 50 dB below the signal peak.

[0042] In the prior art, tapering at the edges of antenna array columns is achieved by reducing power levels of amplifiers feeding radiating elements at the edges of the antenna array column. When substantially identical power amplifiers run at different power levels (i.e., gain settings), the distortions generated by the power amplifiers will be different.

[0043] In some embodiments, the amplifiers are operated at substantially identical operating points to minimize variance in power amplifier distortions to improve global-DPD signal processing. RF observation signals are obtained for each power amplifier at respective observation couplers. The RF observation signals are combined and fed back to a DPD module that may be part of an RFIC. If varied amplifier distortions are present, due to the amplifiers running at different power levels, an aggregated RF observation signal would comprise a mix of said varied amplifier distortions. As a result, the aggregated RF observation signal cannot optimally reflect the distortions at each individual power amplifier, as the individual power amplifiers may have different distortion characteristics with respect to each other. By operating all power amplifiers at a common power level, the aggregated RF observation signal more precisely reflects the distortions at each individual power amplifier, and this leads to better global-DPD.

[0044] With respect to Fig. 6, an FDD 2T2R array column 600 is depicted. FDD transceiver modules such as FDD RF front end circuits 602, 604, 606, 608, 610 each provide two uplink receive paths from antenna elements over lines 642 through receive filters 620, 622 and LNAcircuits 624, 626 providing received RF signals on lines of 628 and 630 to the RF receive combining network. The low power RF transmit distribution network provide signals on lines 638, 640 to the distributed RF power amplifiers 634, 636 which are provided to transmit antenna radiating elements over lines 644 after being filtered by transmit filters 631, 632.

[0045] With respect to Fig. 7, a dual band low power RF transmit distribution network 700 will be described. RFICs 702, 750, provide two polarized RF transmit signals in band 1 (Bill, Bl-V) and in band 3 (B3-H, B3-V), respectively. Each of these four RF transmit signals are provided to low power distribution network 708. In some embodiments preamplifiers or buffer amplifiers 706, 734, 754, 772 provide preamplification of the horizontal RF signals on lines 704, 752 and the vertical RF signals on lines 732, 770. Each RF signal is split using splitters 710, 736, 756, 774 the outputs of which are provided to phase adjustment circuits including, for example, phase adjustment circuits 716, 738, 758, 776, 778, etc. The phase adjustment circuits may be calibrated to remove any differential phase variations from the low power RF transmit distribution network as well as configured to impart additional phase offsets associated with a desired electronic beam tilt. Furthermore, note that the beam tilts imposed for the band one RF signals (Bl-H, Bl-V) maybe different than the electronic beam tilt imparted by phase adjustment circuits operating on band 3 low-power RF transmit signals (B3-H, B3-V). The various phase adjusted low power RF signals are provided to respective RF front end circuits 720, 780 containing four distributed RF power amplifiers 722, 740, 760, 761, whose outputs are filtered by transmit filters 724, 742, 762, 763. Quadriplexers 726 and 764 combine the dual band RF signals for transmission via cross-polarized antenna pair 730 via a horizontal radiating element connected by line 728 and a vertical radiating element connected by line 766. Note that RF front end circuit 780 is configured to drive parallel- connected horizontal radiating elements and parallel-connected vertical radiating elements within the two pairs of cross polarized elements 782, 784.

[0046] With respect to Fig. 8, a dual band RF transmit observation network 800 will be described. Samples of each power amplifier output are obtained by couplers (e.g., 816, 838, etc., in RF front end module (i.e., RF distributed amplifier module) 820, and 848, 850, etc. in RF front end module 860) connected to the output of each power amplifier. For a given RF signal, the various observation signals are combined in a respective signal combiner 810, 834, 844, 846. In Fig. 8, RF observation signal aggregator 808 comprises signal combiners 810, 834, 844, and 846 as well as a respective set of phase adjustment circuits for each signal combiner. In some embodiments, the RF observation signal aggregator only comprises onesignal combiner and an associated set of phase adjusters. In some embodiments, the RF observation signal aggregator only comprises one signal combiner and no phase adjusters.

[0047] The combined observation RF signal is provided to the respective DPD inputs 804, 832, 840, 842 associated with the RF ICs 802, 840. As one example the combined transmit RF observation signal 804 from signal combiner 810 for band Bl-H Is provided to the DPD- H input of RF IC 802. The RF IC 802 uses an observation receiver to compare the combined transmit RF observation signal to the transmitted RF signal 806. The RF IC 802 will update its DPD algorithm and / or DPD mapping tables based on the comparison. Note also that the phase adjustment circuits 812 through 814 are configured to remove any phase differentials associated with the RF transmit observation network, as well as to remove any intentional phase adjustments imposed by the low power RF transmit distribution network for purposes of electronic beam tilt. In at least one embodiment, each RF observation signal aggregator includes a set of phase adjustment circuits configured to remove beam-tilt phase shifts. In other embodiments, a set of phase adjustment circuits configured to remove beam-tilt phase shifts is substantially adjacent to each RF observation signal aggregator. In other embodiments, a set of phase adjustment circuits is not included.

[0048] Furthermore, as mentioned above the electronic beam tilt angles implemented for band 1 signals may be different than the electronic beam tilt angles implemented for band 3 signals, and the various phase offsets associated with the different electronic beam tilt angles may be independently removed by the separate Bl and B3 phase adjustment circuits of the Bl and B3 RF transmit observation networks.

[0049] In embodiments with multiple RF transmit observation networks, each separate RF transmit observation network shall be fed by power amplifiers operating at a common power level associated with that RF transmit observation network. For example, in Fig 8., the power levels of all amplifiers associated with the Bl-H RF transmit observation network shall be substantially identical to each other. The power levels of all amplifiers associated with the Bl-V RF transmit observation network shall be substantially identical to each other. The power levels of all amplifiers associated with the B3-H RF transmit observation network shall be substantially identical to each other. The power levels of all amplifiers associated with the B3-V RF transmit observation network shall be substantially identical to each other. The power levels of amplifiers associated with different RF transmit observation networks need not be substantially identical, as they will not be summed with each other at a signal aggregator.

[0050] With respect to Fig 9, a 4T4R FDD dual band dual column system 900 will be described. The system comprises 2 vertical linear columns 902, 904. Each column comprises cross polarized antenna pairs that are interleaved between transmit and receive antennas. Each RF front end module, including 906, 908, 910, 912, 914, processes dual polarized (V / H) signals in each of two bands (Bl, B3), forming a dual band 2T2R array. This may be viewed equivalently as a 4T4R array. The receive portion of each RF front end module 920 includes two band one receive filters 922, 929 and two band one LNAs 930, 932, as well as two band three receive filters 926, 928 and two band three LNAs 934, 936. Similarly, the transmit portion of each RF front end module 920 includes two band one transmit filters 938, 939, and two band one distributed RF power amplifiers 942, 944, as well as two band three transmit filters 940, 941, and two band three distributed RF transmit power amplifiers 946, 948.

[0051] Fig. 10 depicts antenna array columns 1000, 1050, 1060, and 1080 that may be formed using the distributed amplifier radio frequency (RF) transceiver chains described above. An RF distributed amplifier module 1016 is configured to produce a respective amplified RF signal with a power level that is substantially equal the power level produced by the other power amplifiers depicted in Fig. 10. For receive chains a low-noise amplifier may be used. Within distributed amplifier RF transceiver chain 1002 is a RF distributed amplifier module 1016 positioned substantially adjacent to a tapering subarray of cross polarized antennas 1014 and 1020. A band pass filter may be included after a distributed amplifier module, e.g., at connection point 1018, or before the distributed amplifier module. Each distributed amplifier RF transceiver chain is associated with a single RF transmit signal, and a pair of such distributed amplifier configurations may be used to drive a column of cross-polarized antenna elements.

[0052] Within the antenna array column 1000, an RF distributed amplifier module of a set of RF distributed amplifier modules is connected to and positioned substantially adjacent to a nominal subarray of one or more radiating elements at RF distributed amplifier transceiver chains 1006 and 1008. An RF distributed amplifier module of the set of RF distributed amplifier modules is connected to and positioned substantially adjacent to tapering subarrays having more radiating elements than the nominal subarray in RF distributed amplifier transceiver chains 1002, 1004, 1010 and 1012.

[0053] Each distribution network includes (i) a low-power RF transmit distribution network configured to distribute transmit RF signals (e.g., two such transmit signals in a 2T2R configuration) to each of the respective RF power amplifiers within the RF TRX elements,(ii) an RF transmit observation network configured to obtain RF transmit observation signals from the various observation couplers within the RF TRX circuits and to combine them into one or more aggregated RF transmit observation signals, and, in FDD configurations, (iii) separate RF receive combiner networks configured to combine receive RF signals from outputs configured to accept a transmit RF signal source, such as a modulated RF signal from an RF integrated circuit (RFIC), that is provided to a low-power RF transmit distribution network for providing the analog RF signal to a plurality of RF power amplifiers distributed throughout the antenna array. The RF power amplifiers, in turn, shall be distributed along the columns of the example antenna array columns 1000, 1050, 1060, and 1080 such that they are positioned substantially adjacent to their associated radiating antenna elements.

[0054] In Fig. 10., the antenna array column 1050 comprises a centered nominal subarray of one radiating element. Immediately above the nominal subarray is a tapering subarray of two radiating elements. Immediately below the nominal subarray is a second tapering subarray of two radiating elements. At the edges of the antenna array column 1050 are third and fourth tapering subarrays of two radiating elements each.

[0055] In the previously described antenna array column 1050, a nominal subarray is positioned closer to a center of the antenna array column 1050 than at least one tapering subarray. The tapering subarray has a greater number of radiating elements than the nominal subarray. The second, third, and fourth tapering subarrays have the same number of radiating elements as the tapering subarray.

[0056] The antenna array column 1060 comprises two centered nominal subarrays of two radiating elements each. Adjacent to the nominal subarrays and at the top of antenna array column 1050 is a tapering subarray of three radiating elements. At the bottom of antenna array column 1050 is a second tapering subarray that also has three radiating elements.

[0057] In the previously described antenna array column 1060, two nominal subarrays are positioned closer to a center of the antenna array column than the tapering subarray. The tapering subarray has a greater number of radiating elements than the nominal subarray. The second tapering subarray at the bottom has the same number of radiating elements as the tapering subarray at the top.

[0058] In Fig. 10., the antenna array column 1080 comprises a centered nominal subarray of one radiating element. Adjacent to the nominal subarray are two tapering subarrays of two radiating elements each. At the edges of the antenna array column 1080 are two second tapering subarrays of three radiating elements each.

[0059] In the above-described antenna array column 1080, one or more nominal subarrays are positioned closer to a center of the antenna array column than the at least one tapering subarray and the at least one tapering subarray is positioned closer to a center of the antenna array column than the at least one second tapering subarray. The at least one tapering subarray has a greater number of radiating elements than the nominal subarray. The at least one second tapering subarray has a greater number of radiating elements than the tapering sub array.

[0060] A nominal subarray is a subarray with a least number of associated radiating elements in the antenna array column. A tapering subarray is a subarray with a greater number of associated radiating elements than the nominal subarray. Second, third, fourth, etc. tapering subarrays may have equal or varying numbers of associated radiating elements with respect to the tapering subarray. In general, it is preferred, but not required, to maintain reflective symmetry when selecting the positions and number of associated radiating elements for each sub array.

[0061] All the RF power amplifiers are configured to output a common power level. The common power level from each power amplifier is divided evenly across all the radiating elements of the associated subarray. Tapering subarrays are named as such as they will split the common power level across a greater number or radiating elements than nominal subarrays. By sharing the common power level across a greater number of radiating elements, each individual radiating element in a tapering subarray will operate with less power than each individual radiating element in a nominal subarray, thereby achieving tapering of the signal. Various configurations of one or more nominal subarrays and one or more tapering subarrays may be used, as exemplified by Fig. 10. The example antenna array columns 1000, 1050, 1060, and 1080 may each be used to impart tapering across a distributed RF signal. One with experience in the art would understand that other antenna array configurations having at least one nominal subarray and at least one tapering subarray may be used as well.

[0062] In array 1050, individual cross polarized radiating elements within the tapering subarrays each receive 1 / 2 as much RF power when compared to the cross polarized radiating element in the nominal subarray. In array 1060, individual cross polarized radiating elements within the tapering subarrays each receive 2 / 3 as much RF power when compared to individual cross polarized radiating elements in the nominal subarrays. In array 1080, individual cross polarized radiating elements within the top and bottom tapering subarrays each receive 1 / 3 as much RF power when compared to the cross polarized radiating elementin the nominal subarray, and individual cross polarized radiating elements within the more central tapering subarrays each receive 1 / 2 as much RF power when compared to the cross polarized radiating element in the nominal subarray.

[0063] Fig. 11 shows a typical resonant cavity filter (or simply, a cavity filter) having a resonator 1104 within a cavity 1102. Cavity filters are a type of electronic filter that uses the resonance of the cavities to achieve a frequency selectivity, typically in the form of a bandpass filter. The cavities are typically formed by metallic walls or surfaces that create a resonant structure. The dimensions of the cavities are designed to resonate at the desired frequency or frequencies. Resonant cavities exhibit a high selectivity for specific frequencies, and the cavities are tuned to resonate at the desired frequency allowing signals close to this frequency to pass through while attenuating signals at other frequencies. The resonance is highly dependent upon the height of the cavity. Cavity filters typically incorporate tuning mechanisms to adjust the resonance frequency. This allows for fine tuning the filter to meet the specific requirements of the application. Multiple resonant cavities are combined in an array to create more complex filters with broader pass bands or improved rejection characteristics. The resonant cavities are combined by providing windows in the cavity walls from one cavity to adjacent cavities. In resonant cavity 1100, note the high current density regions 1108 imposed in the cavity side walls that pass through to the top and bottom of the cavity towards the highest current density 1110 and in particular (“hotspot” regions) 1106, as well as 1112. Resonance of the cavity filter is highly dependent upon the electrical connectivity between the cavity walls and the cavity top and bottom.

[0064] In contrast to the resonant cavity filters, a ceramic resonator 1204 shown in Fig. 12 supported by a passive post element 1206 and placed in an enclosure 1202, demonstrates a frequency selectivity that is primarily a function of the resonator 1204 material, shape, and size, and is highly independent of the enclosure size and shape. This is due largely to the fact that the enclosure does not form a significant part of the resonating structure. Note the low magnitude of the currents induced in the enclosure sidewalls 1208, 1212, being primarily in the horizontal plane of the resonator 1206, and the very low currents 1214 flowing from the sidewalls to the top or bottom regions 1210.

[0065] In some embodiments, the transmit filters comprise one or more groups of crosscoupled ceramic resonators, where the coupling between resonators is directly between the multiple resonator elements, that is, from each such resonator to each other resonator (i.e., cross-coupled). In such cross-coupled resonator filters, no resonator elements are fullyisolated from each other resonator elements. The resonator elements in some embodiments are characterized by a TEoid resonance mode. The resonator elements may be ceramic discs to provide rotational symmetry for ease of assembly, but other shapes may be used such as square or oblong shapes.

[0066] Cavity filters are only able to achieve couplings to immediately adjacent cavities via openings, or apertures, in the cavity walls between the adjacent cavities, rather than between each cavity of a set of cavity resonators. Unlike cavity resonator filters, the enclosure primarily serves as shield to block external radiation from occurring, and it does not substantially participate in determining the resonance frequency of the resonators. The crosscoupled resonator elements configured as a filter also have signal less loss when compared to cavity filters. The reduced signal loss associated with the direct cross-coupled resonator elements, together with elimination of RF signal loss of the amplified RF signals associated with power distribution (e.g., splitters, phase adjusters, and associated RF cabling networks used to distribute power amplifier output signals to an array of radiating elements) allows some embodiments to use of LDMOS amplifiers rather than GaN-based power amplifiers, which suffer from reduced linearity.

[0067] Fig. 13 depicts a filter assembly 1300 having two TX and two RX filter regions. TX filter regions 1302 and 1304 each comprise three sets of cross-coupled resonators, crosscoupled resonators 1306 - 1310 and 1312 - 1316 respectively, where each set of crosscoupled resonators includes three ceramic resonator elements. Each of the three crosscoupled sets are themselves coupled to an adjacent set through an aperture (e.g., aperture 1318) in the enclosure wall 1320. In the embodiment shown, each of the RX filter regions 1322 and 1324 comprise single sets of three cross-coupled resonators.

[0068] The cross-coupled resonator filters may comprise an array of resonators, including a substantially linear one-dimensional array. “Substantially linear” refers to a set of resonators arranged in a line, where one or more of the resonators may be slightly offset from the line to increase their coupling coefficients to non-adjacent resonator elements further along the array.

[0069] Alternative embodiments may extend to a 2-dimensional array of resonators within a single enclosure. Some embodiments of 2-dimensional arrays include two substantially linear array rows positioned substantially parallel to each other. The resonators within each row may have may include slight offsets to alter the couplings between elements along it's linear set as well as the couplings to resonators in the adjacent row.

[0070] The signal input port and output port to the resonator elements are provided by signal couplers. The filter frequency responses are generally symmetric between ports, and no distinction is necessary between an “input” port and an “output” port. Because signal inputs and outputs are interchangeable in the description, the terms port 1 and port 2 will be used with the understanding that if an input signal is provided at port 1, then port 2 will have the output signal and vice versa. The coupling probes used to couple signals from RF conductors to and from the resonating elements may have a concentric arc that conforms to the curvature of a given resonator element. Input / output coupling probes maybe also placed between resonating elements, and the coupling to a specific resonator may be achieved by positioning its arc concentrically around that resonator. Embodiments of the filter having this probe configuration provides a relocation of a transfer function “zero” from the low band to the high band to provide faster roll-off when desired, such as in an FDD embodiment where the transmit and receive frequency bands are immediately adjacent to each other.

[0071] Fig. 14 shows a further embodiment 1400 of two TX filter structures for use in a 2T RF front end module. The sets of cross-coupled resonators each have an enclosure wall 1402, 1404, respectively. A slight variation of the enclosure is shown by enclosure wall 1434, which encloses the set of cross-coupled resonator elements 1420, 1422, 1424, 1426, 1428, and 1430. The enclosure walls may be formed from a single length of a sheet-like metal, such as brass, which is then folded into the desired enclosure shape. Tabs may be provided for alignment of the enclosure during manufacturing. In some embodiments, the enclosure walls may be soldered to the enclosure base using a solder reflow process.

[0072] The TX filters of Fig. 14 comprise two substantially linear rows placed adjacent to each other. Note that resonator element 1424 is slightly offset within the first linear row of elements 1420, 1422, 1424, 1426, to increase the coupling coefficient to element 1420. In some embodiments, wall extensions may be interposed between resonator elements to also adjust the respective coupling coefficients, such as the stub-wall extension 1436 that reduces the coupling between resonator elements 1424 and 1430, and to a lesser extent, the coupling between elements 1422 and 1430.

[0073] Fig. 15 depicts an exploded view 1500 of RF front end module 1550, comprising a filter wall enclosure 1504, an enclosure top 1502, a filter enclosure bottom 1506. The isolation enclosure 1508 provides interference mitigation for electrical components such as the distributed power amplifiers, LNAs, circulators, duplexers, or quadriplexers mounted on base 1510, which may also provide a heat sink function. RF front end module 1560 is analternative embodiment of the assembly comprising a filter wall enclosure 1562, an enclosure top 1564, and a filter enclosure bottom 1566. The isolation posts 1568 attached to mounting plate 1570, provides interference mitigation for electrical components via physical distancing. The isolation enclosure 1574 provides further interference mitigation for electrical components such as the distributed power amplifiers, LNAs, circulators, duplexers, or quadriplexers mounted on base 1572, which may also provide a heat sink function. In some embodiments, the RF front end modules of the distributed RF amplifier chains may be designed to be in conformance with IP-67 specifications by employing waterproof seals (e.g., seal 1576). However, in some embodiments the modules are designed to be enclosed by a radome and are compliant with the less stringent requirements of IP-55.

[0074] Fig. 16 depicts an active antenna apparatus 1600 having two antenna radiating columns 1602, 1604, and respective associated RF distribution networks 1610, 1612. The Fronthaul Gateway board (FHGW) 1630 includes digital baseband transmit processor(s) 1632, that provides digital data to the transmit circuit TX RFIC 1614, which in turn converts the digital data to RF signals for distribution among the TRX devices. The FHGW 1630 also includes digital baseband receive processor(s) 1634, which receive digital baseband data from the RX RFIC 1618, which converts RF signals originating from the TRX devices and received via the RF distribution networks 1610, 1612. The front hall gateway 1630 also includes an observation receiver 1636 and a general purpose I / O (GPIO) circuit 1638 for communicating with the corresponding observation receiver and GPIO interfaces 1620, 1622. Power supply unit (PSU) 1640 provides necessary voltages to the system boards 1606, 1608, 1630.

[0075] Fig. 17 depicts an embodiment 1700 comprising a low-power RF distribution network, an RF distributed antenna array, and a digital predistortion (DPD) module. Low- power RF signal 1702 is split into a plurality of low-power RF signals at a low-power RF distribution network 1704. The splitting may be achieved by using a N-way power splitter as described in relation to Fig. 4. The low-power RF distribution network 1704 provides the plurality of low-power RF signals to a set of RF distributed amplifier modules 1708, 1720, and 1730 which are distributed along an antenna array column 1706. Each RF distributed amplifier module may be part of a respective RF transceiver chain or RF front end module. The antenna array column 1706 comprises subarrays of one or more radiating elements 1712, 1724, and 1734. Each of the RF distributed amplifier modules 1708, 1720, and 1730 include, at least, a RF power amplifier, the power amplifiers 1710, 1722, and 1732, respectively.

[0076] In some embodiments, each of the RF distributed amplifier modules 1708, 1720, and 1730 include a respective phase adjustment circuit, configured to apply a respective beam-tilt phase shift to each of the plurality of low-power RF signals, such as the 4-bit switched delays described in relation to Fig. 4. In embodiments wherein RF distributed amplifier modules include a phase adjustment circuit, respective phase shift control signals are supplied to each RF distributed amplifier module via the low-power RF distribution network 1704 or via a separate phase shift control signal distribution network. In other embodiments, a set of phase adjustment circuits is included within the low-power RF distribution network 1704. In other embodiments, a set of phase adjustment circuits is included within or substantially near an RF digital-to-analog converter (RF DAC) that feeds into the low-power RF distribution network 1704.

[0077] In some embodiments, each of the RF distributed amplifier modules 1708, 1720, and 1730 include a respective bandpass filter, configured to limit out of band energy for each of the plurality of low-power RF signals, such as the filters described in relation to Figs. 11 - 14.

[0078] In some embodiments, each of the RF distributed amplifier modules 1708, 1720, and 1730 include at least one quadriplexer, configured to combine RF of a same polarity and different bands, such as the quadriplexers 726 and 764 of Fig 7.

[0079] In general, each of the RF distributed amplifier modules 1708, 1720, and 1730 may include a plurality of RF power amplifiers and other electrical components and may be designed to handle Tx and Rx for various polarities and bands. Figs. 6 - 9 depict numerous examples of such. An RF distributed amplifier module may be an RF transceiver chain or may be an element or group of elements of an RF transceiver chain as described herein. An RF distributed amplifier module may be an RF frontend module or may be an element or group of elements of an RF frontend module as described herein. In all cases, each of the RF distributed amplifier modules comprises at least a power amplifier.

[0080] RF distributed amplifier module 1720 is connected to and positioned substantially adjacent to a nominal subarray 1724. RF distributed amplifier module 1708 is connected to and positioned substantially adjacent to a tapering subarray 1712. RF distributed amplifier module 1730 is connected to and positioned substantially adjacent to a tapering subarray 1734.

[0081] Each RF distributed amplifier module 1708, 1720, and 1730 is configured to produce a respective amplified RF signal with a substantially equal (i.e., common) power level. In atleast one embodiment, the common power level is achieved due to each RF distributed amplifier module 1708, 1720, and 1730 being substantially identical and configured to operate at a common gain. In at least one embodiment, the common power level is achieved due to each RF power amplifier 1710, 1722, and 1732 being substantially identical and configured to operate at a common gain.

[0082] Tapering subarray 1712 comprises cross polarized radiating elements 1714 and 1716. In at least one embodiment, the cross polarized radiating elements 1714 and 1716 are wired in parallel and evenly split the RF power provided to the tapering subarray 1712. Nominal subarray 1712 comprises cross polarized radiating element 1726. Second tapering subarray 1734 comprises cross polarized radiating elements 1736 and 1738. In at least one embodiment, the cross polarized radiating elements 1736 and 1738 are wired in parallel and evenly split the RF power provided to the second tapering subarray 1734.

[0083] As depicted in embodiment 1700, the tapering subarray 1712 and second tapering subarray 1734 have more radiating elements than the nominal subarray 1724. In embodiment 1700, cross polarized radiating elements 1714, 1716, 1736 and 1738 each receive half as much RF power when compared to cross polarized radiating element 1726.

[0084] An observation coupler 1718 is connected to the RF distributed amplifier module 1708 and is configured to produce a first RF observation signal. An observation coupler 1728 is connected to the RF distributed amplifier module 1720 and is configured to produce a second RF observation signal. An observation coupler 1740 is connected to the RF distributed amplifier module 1730 and is configured to produce a third RF observation signal.

[0085] An RF observation signal aggregator 1742 is configured to combine at least the first RF observation signal and the second RF observation signal to produce an aggregated RF observation signal. Depicted in embodiment 1700, the RF observation signal aggregator 1742 combines at least the first RF observation signal, the second RF observation signal, and the third RF observation signal, to produce the aggregated RF observation signal.

[0086] In some embodiments, a third RF transceiver chain comprising elements 1730 - 1740 is not included and the RF observation signal aggregator 1742 is configured to combine at least the first RF observation signal and the second RF observation signal to produce an aggregated RF observation signal.

[0087] In at least one embodiment, and depicted in Fig. 17, the nominal subarray 1724 is positioned closer to a center of the antenna array column 1706 than the tapering subarray 1712. The third RF distributed amplifier module 1730 is connected to and positionedsubstantially adjacent to the second tapering subarray 1734. The second tapering subarray 1734 comprises an equal number of radiating elements as the tapering subarray 1712. The third observation coupler 1740, connected to the third RF distributed amplifier module 1730, is configured to produce a third RF observation signal. The RF observation signal aggregator 1742 is configured to combine at least the first RF observation signal, the second RF observation signal, and the third RF observation signal, to produce the aggregated RF observation signal. Examples of similar antenna array columns can be seen in Fig. 10. The antenna array column 1050 comprises a centered nominal subarray of one radiating element. Immediately above and below the nominal subarray are tapering subarrays of two radiating elements each. At the edges of the antenna array column 1050 are two second tapering subarrays of two radiating elements each. The antenna array column 1060 comprises centered nominal subarrays of two radiating elements each. Adjacent to the nominal subarrays and at the top of the column is a tapering subarray of three radiating elements. At the bottom of the antenna array column 1050 is a second tapering subarray that also has three radiating elements.

[0088] In the previously described antenna array column examples, one or more nominal subarrays are positioned closer to a center of the antenna array column than the at least one tapering subarray. The at least one tapering subarray has a greater number of radiating elements than the nominal subarray. The at least one second tapering subarray has the same number of radiating elements as the tapering subarray.

[0089] In at least one embodiment, and depicted in Fig. 17, the nominal subarray 1724 is positioned in between the tapering subarray 1712 and the second tapering subarray 1734.

[0090] In at least one embodiment, a set of phase adjustment circuits within the low-power RF distribution network 1704 is configured to apply a respective beam -tilt phase shift to each of the plurality of low-power RF signals. In such embodiments, a set of phase adjustment circuits within the observation signal aggregator 1742 is configured to remove the applied beam-tilt phase shifts. In at least one embodiment, the observation signal aggregator 1742 is housed within the antenna array column 1706. In other embodiments, the observation signal aggregator 1742 is part of an observation signal distribution network. In at least one embodiment, the observation signal aggregator 1742 is part of an RFIC.

[0091] In some embodiments, at least one ceramic resonator element is connected to each RF distributed amplifier module in the set of RF distributed amplifier modules 1708, 1720, and1730. The at least one ceramic resonator element may be used to limit or filter out of band power of the associated signal.

[0092] In at least one embodiment that is not depicted in Fig. 17, a third RF distributed amplifier module of the set of RF distributed amplifier modules connected to and positioned substantially adjacent to a second tapering subarray of three or more radiating elements. The second tapering subarray comprises more radiating elements than the tapering subarray. A third observation coupler, connected to the third RF distributed amplifier module, is configured to produce a third RF observation signal. The RF observation signal aggregator is configured to combine at least the first RF observation signal, the second RF observation signal, and the third RF observation signal, to produce the aggregated RF observation signal. In such an embodiment, the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray, and the tapering subarray is positioned closer to the center of the antenna array column than the second tapering subarray. An example of such an antenna array column can been seen in Fig. 10. The antenna array column 1080 comprises a centered nominal subarray of one radiating element. Adjacent to the nominal subarray are two tapering subarrays of two radiating elements each. At the edges of the antenna array column 1080 are two second tapering subarrays of three radiating elements each.

[0093] In the above-described antenna array column example, one or more nominal subarrays are positioned closer to a center of the antenna array column than the at least one tapering subarray and the at least one tapering subarray is positioned closer to a center of the antenna array column than the at least one second tapering subarray. The at least one tapering subarray has a greater number of radiating elements than the nominal subarray. The at least one second tapering subarray has a greater number of radiating elements than the tapering sub array.

[0094] A DPD module 1744 is configured to modify the low-power RF signal 1702, and to update a parameter of the DPD module 1744 based at least in part on the aggregated RF observation signal produced by the RF observation signal aggregator 1742. In at least one embodiment, the parameter of the DPD module 1744 is a generalized memory polynomial coefficient. In at least one embodiment, the parameter of the DPD module 1744 is an IQ value in a DPD lookup table.

[0095] In at least one embodiment, an RF DAC is configured to produce the low-power RF signal. In such an embodiment the DPD module is further configured to replace an initial IQ point with a DPD-adjusted IQ point and output the DPD-adjusted IQ point to the RF DAC.

[0096] In Fig. 17, a stream of digital IQ points 1746 is input to the DPD module 1744 via an RFIC 1750. A DPD-adjusted output of the DPD module 1744 is input to an RF DAC 1748. The RF DAC 1748 is configured to produce the low-power RF signal 1702.

[0097] The DPD module 1744 is configured to implement at least one DPD method and to generate a stream of DPD-adjusted IQ points. The RF DAC 1748 is configured to convert the stream DPD-adjusted IQ points into the low-power RF signal 1702.

[0098] In at least one embodiment, the DPD module 1744 and RF DAC 1748 are part of an RFIC 1750, for example the RF ICs 802 and 840 of Fig. 8.

[0099] Fig. 18 depicts a method 1800 for updating a digital predistortion (DPD) module parameter, in accordance with some embodiments, (note that the term “step” as used herein is not intended to impart or imply a specific required sequence to the methodology described).

[0100] Step 1802 comprises splitting a low-power RF signal into a plurality of low-power RF signals using a low-power RF distribution network.

[0101] Step 1804 comprises distributing the plurality of low-power RF signals using the low- power RF distribution network to a set of RF distributed amplifier modules positioned within an antenna array column.

[0102] Step 1806 comprises generating a first amplified RF signal having a common power level using a first RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the first RF distributed amplifier module is connected to and positioned substantially adjacent to a nominal subarray of one or more radiating elements.

[0103] Step 1808 comprises generating a second amplified RF signal having the common power level using a second RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the second RF distributed amplifier module is connected to and positioned substantially adjacent to a tapering subarray having more radiating elements than the nominal subarray.

[0104] Step 1810 comprises obtaining a first RF observation signal using a first observation coupler connected to the first RF distributed amplifier module.

[0105] Step 1812 comprises obtaining a second RF observation signal using a second observation coupler connected to the second RF distributed amplifier module.

[0106] Step 1814 comprises combining at least the first RF observation signal and the second RF observation signal using an RF observation signal aggregator to produce an aggregated RF observation signal.

[0107] Step 1816 comprises updating a parameter of a DPD module based at least in part on the aggregated RF observation signal, wherein the DPD module is configured to modify the low-power RF signal.

[0108] In at least one embodiment, each RF distributed amplifier modules in the set of RF distributed amplifier modules is substantially identical and configured to operate at a common gain.

[0109] In at least one embodiment, the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray.

[0110] In at least one embodiment, the method 1800 further comprises (i) generating a third amplified RF signal having the common power level using a third RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the third RF distributed amplifier module is connected to and positioned substantially adjacent to a second tapering subarray having more radiating elements than the nominal subarray, (ii) obtaining a third RF observation signal using a third observation coupler connected to the third RF distributed amplifier module, and (iii) combining at least the first RF observation signal, the second RF observation signal, and the third RF observation signal using the RF observation signal aggregator to produce the aggregated RF observation signal.[OHl] In some embodiments with the third RF distributed amplifier module that is connected to and positioned substantially adjacent to the second tapering subarray having more radiating elements than the nominal subarray, the nominal subarray is positioned in between the tapering subarray and the second tapering subarray.

[0112] In at least one embodiment, each radiating element of the nominal subarray is wired in parallel, and each radiating element of the tapering subarray is wired in parallel.

[0113] In at least one embodiment, the method 1800 further comprises (i) applying a respective beam-tilt phase shift to each of the plurality of low-power RF signals using a set of phase adjustment circuits within the low-power RF distribution network, and (ii) removing the applied beam-tilt phase shifts using a set of phase adjustment circuits within the observation signal aggregator.

[0114] In at least one embodiment, the method 1800 further comprises bandpass filtering the plurality of low-power RF signals using at least one ceramic resonator element connected to each RF distributed amplifier module in the set of RF distributed amplifier modules.

[0115] In at least one embodiment, the method 1800 further comprises (i) generating a third amplified RF signal having the common power level using a third RF distributed amplifiermodule of the set of RF distributed amplifier modules, wherein the third RF distributed amplifier module is connected to and positioned substantially adjacent to a second tapering subarray having more radiating elements than the tapering subarray, (ii) obtaining a third RF observation signal using a third observation coupler connected to the third RF distributed amplifier module, and (iii) combining at least the first RF observation signal, the second RF observation signal, and the third RF observation signal using the RF observation signal aggregator to produce the aggregated RF observation signal.

[0116] In some embodiments with the third RF distributed amplifier module that is connected to and positioned substantially adjacent to the second tapering subarray having more radiating elements than the tapering subarray, the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray, and the tapering subarray is positioned closer to the center of the antenna array column than the second tapering subarray.

[0117] In at least one embodiment, updating the parameter of the DPD module based at least in part on the aggregated RF observation signal comprises updating a generalized memory polynomial coefficient.

[0118] In at least one embodiment, updating the parameter of the DPD module based at least in part on the aggregated RF observation signal comprises updating an IQ value in a DPD lookup table.

[0119] At least one embodiment further comprises an RF DAC generating the low-power RF signal. In such an embodiment, the DPD module is configured to modify the low-power RF signal at least in part by replacing an initial IQ point with a DPD-adjusted IQ point and outputting the DPD-adjusted IQ point to the RF DAC. The DPD module and RF DAC may be part of an RFIC or may be independent elements.

Claims

Claims:

1. An apparatus comprising: a low-power RF distribution network configured to split a low-power RF signal into a plurality of low-power RF signals, and to provide the plurality of low-power RF signals to a set of RF distributed amplifier modules; the set of RF distributed amplifier modules being distributed along an antenna array column, each RF distributed amplifier module in the set of RF distributed amplifier modules being configured to produce a respective amplified RF signal with a substantially equal power level; a first RF distributed amplifier module of the set of RF distributed amplifier modules connected to and positioned substantially adjacent to a nominal subarray of one or more radiating elements; a second RF distributed amplifier module of the set of RF distributed amplifier modules connected to and positioned substantially adjacent to a tapering subarray having more radiating elements than the nominal subarray; a first observation coupler, connected to the first RF distributed amplifier module, configured to produce a first RF observation signal; a second observation coupler, connected to the second RF distributed amplifier module, configured to produce a second RF observation signal; an RF observation signal aggregator configured to combine at least the first RF observation signal and the second RF observation signal, and to produce an aggregated RF observation signal, and; a DPD module configured to modify the low-power RF signal, and to update a parameter of the DPD module based at least in part on the aggregated RF observation signal.

2. The apparatus of claim 1, wherein each RF distributed amplifier module in the set of RF distributed amplifier modules is substantially identical and configured to operate at a common gain.

3. The apparatus of claim 1, further comprising an RF DAC configured to produce the low-power RF signal, wherein the DPD module is further configured to replace an initial IQ point with a DPD-adjusted IQ point and output the DPD-adjusted IQ point to the RF DAC.

4. The apparatus of claim 1, wherein the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray.

5. The apparatus of claim 1, further comprising: a third RF distributed amplifier module of the set of RF distributed amplifier modules connected to and positioned substantially adjacent to a second tapering subarray having an equal number of radiating elements as the tapering subarray; a third observation coupler, connected to the third RF distributed amplifier module, configured to produce a third RF observation signal; the RF observation signal aggregator being configured to combine at least the first RF observation signal, the second RF observation signal, and the third RF observation signal, to produce the aggregated RF observation signal.

6. The apparatus of claim 5, wherein the nominal subarray is positioned in between the tapering subarray and the second tapering subarray.

7. The apparatus of claim 1, wherein each radiating element of the nominal subarray is wired in parallel, and each radiating element of the tapering subarray is wired in parallel.

8. The apparatus of claim 1, further comprising: a set of phase adjustment circuits within the low-power RF distribution network configured to apply a respective beam-tilt phase shift to each of the plurality of low-power RF signals, and; a set of phase adjustment circuits within the observation signal aggregator configured to remove the applied beam-tilt phase shifts.

9. The apparatus of claim 1, further comprising at least one ceramic resonator element connected to each RF distributed amplifier module in the set of RF distributed amplifier modules.

10. The apparatus of claim 1, further comprising: a third RF distributed amplifier module of the set of RF distributed amplifier modules connected to and positioned substantially adjacent to a second tapering subarray of three or more radiating elements; a third observation coupler, connected to the third RF distributed amplifier module, configured to produce a third RF observation signal; the RF observation signal aggregator being configured to combine at least the first RF observation signal, the second RF observation signal, and the third RF observation signal, to produce the aggregated RF observation signal.

11. The apparatus of claim 10, wherein the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray, and the tapering subarray is positioned closer to the center of the antenna array column than the second tapering subarray.

12. The apparatus of claim 1, wherein the parameter of the DPD module is a generalized memory polynomial coefficient.

13. The apparatus of claim 1, wherein the parameter of the DPD module is an IQ value in a DPD lookup table.

14. A method comprising: splitting a low-power RF signal into a plurality of low-power RF signals using a low- power RF distribution network; distributing the plurality of low-power RF signals using the low-power RF distribution network to a set of RF distributed amplifier modules positioned within an antenna array column;generating a first amplified RF signal having a common power level using a first RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the first RF distributed amplifier module is connected to and positioned substantially adjacent to a nominal subarray of one or more radiating elements; generating a second amplified RF signal having the common power level using a second RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the second RF distributed amplifier module is connected to and positioned substantially adjacent to a tapering subarray having more radiating elements than the nominal sub array; obtaining a first RF observation signal using a first observation coupler connected to the first RF distributed amplifier module; obtaining a second RF observation signal using a second observation coupler connected to the second RF distributed amplifier module; combining at least the first RF observation signal and the second RF observation signal using an RF observation signal aggregator to produce an aggregated RF observation signal, and; updating a parameter of a DPD module based at least in part on the aggregated RF observation signal, wherein the DPD module is configured to modify the low-power RF signal.

15. The method of claim 14, wherein each RF distributed amplifier module in the set of RF distributed amplifier modules is substantially identical and configured to operate at a common gain.

16. The method of claim 14, further comprising an RF DAC generating the low-power RF signal, wherein the DPD module is configured to modify the low-power RF signal at least in part by replacing an initial IQ point with a DPD-adjusted IQ point and outputting the DPD- adjusted IQ point to the RF DAC.

17. The method of claim 14, wherein the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray.

18. The method of claim 14, further comprising: generating a third amplified RF signal having the common power level using a third RF distributed amplifier module of the set of RF distributed amplifier modules, wherein the third RF distributed amplifier module is connected to and positioned substantially adjacent to a second tapering subarray having more radiating elements than the nominal subarray; obtaining a third RF observation signal using a third observation coupler connected to the third RF distributed amplifier module; combining at least the first RF observation signal, the second RF observation signal, and the third RF observation signal using the RF observation signal aggregator to produce the aggregated RF observation signal.

19. The method of claim 18, wherein the nominal subarray is positioned in between the tapering subarray and the second tapering subarray.

20. The method of claim 14, wherein each radiating element of the nominal subarray is wired in parallel, and each radiating element of the tapering subarray is wired in parallel.

21. The method of claim 14, further comprising: applying a respective beam-tilt phase shift to each of the plurality of low-power RF signals using a set of phase adjustment circuits within the low-power RF distribution network, and; removing the applied beam-tilt phase shifts using a set of phase adjustment circuits within the observation signal aggregator.

22. The method of claim 14, further comprising bandpass filtering the plurality of low- power RF signals using at least one ceramic resonator element connected to each RF distributed amplifier module in the set of RF distributed amplifier modules.

23. The method of claim 14, further comprising: generating a third amplified RF signal having the common power level using a third RF distributed amplifier module of the set of RF distributed amplifier modules, wherein thethird RF distributed amplifier module is connected to and positioned substantially adjacent to a second tapering subarray having more radiating elements than the tapering subarray; obtaining a third RF observation signal using a third observation coupler connected to the third RF distributed amplifier module; combining at least the first RF observation signal, the second RF observation signal, and the third RF observation signal using the RF observation signal aggregator to produce the aggregated RF observation signal.

24. The method of claim 23, wherein the nominal subarray is positioned closer to a center of the antenna array column than the tapering subarray, and the tapering subarray is positioned closer to the center of the antenna array column than the second tapering subarray.

25. The method of claim 14, wherein updating the parameter of the DPD module based at least in part on the aggregated RF observation signal comprises updating a generalized memory polynomial coefficient.

26. The method of claim 14, wherein updating the parameter of the DPD module based at least in part on the aggregated RF observation signal comprises updating an IQ value in a DPD lookup table.

27. An apparatus comprising: a plurality of RF front end distributed amplifier modules distributed along an antenna array column, each distributed amplifier module having at least a pair of power amplifiers interconnected to respective pairs of cross-polarized radiating antenna elements, and wherein the pair of power amplifiers are positioned substantially adjacent to the associated radiating antenna elements; at least a pair of low-power RF transmit distribution networks, each having a set of phase shifter circuits, and configured to distribute a respective low-power transmit RF signal to the each pair of amplifiers of the plurality of RF front end distributed amplifier modules; at least a pair of RF transmit observation networks, each comprising a set of observation couplers and a respective set of observation phase shifter circuits, connected to an observation signal combiner, the transmit observation networks configured to obtain RFtransmit observation signals from the set of observation couplers and to combine them into respective aggregated RF transmit observation signals; at least one RF transceiver circuit having at least two RF modulator outputs and at least two observation receivers, and two digital pre-distortion circuits, and configured to output at least a pair of RF transmit signals to the respective low-power RF transmit distribution networks, wherein the transmit signals have been digitally pre-distorted based on the respective aggregated RF transmit observation signals processed by the observation receivers.

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