Patent Publication Number: US-11664590-B2

Title: Programmable beamforming system including element-level analog channelizer

Description:
DOMESTIC PRIORITY 
     This application is a division of U.S. patent application Ser. No. 15/861,398, filed Jan. 3, 2018, which is a division of U.S. patent application Ser. No. 14/489,715, filed Sep. 18, 2014, now U.S. Pat. No. 10,027,026, issued Jul. 17, 2018, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     This invention was made with Government support under Contract No.: HR0011-14-C-0002 awarded by the Department of Defense. The Government has certain rights in this invention. 
    
    
     BACKGROUND 
     The present disclosure relates to electronic signal processing, and more specifically, to directional signal transmission and/or reception. 
     Hardware implementations of wideband systems are inhibited with respect to the increased demand for bandwidth requirements. One technique used to address the increase in bandwidth requirements is to reduce a signal band into a plurality of sub-bands using a channelizer. Each of the sub-bands can then be processed on parallel channels. Conventional beamforming systems require digital channelizers to mix down the incoming radio frequency (RF) signal at the channelizer array level, which results in very low spurious content. Further, a digital channelizer typically requires a field-programmable gate array (FPGA), which inherently limits the system from sampling high frequency signals such as frequencies operating in the K u  band. 
     SUMMARY 
     According to at least one embodiment, a beamforming system includes a plurality of channelizers and an electronic channel switching module in signal communication with the channelizers. Each channelizer is configured to receive a respective input radio frequency signal and to generate a plurality of respective channels in response to downsampling the respective input radio frequency signal. The channel switching module includes a channel combining circuit configured to selectively combine a common channel generated by each channelizer to form at least one steered analog beam. 
     According to another embodiment, a method of beamforming a radio frequency signal comprises downsampling an incoming radio frequency signal to generate a plurality of polyphase lanes. The method further comprises generating a plurality of channel sets based on the polyphase lanes. Each channel set includes a plurality of channels. The method further comprises selectively combining a common channel of each channel set to form at least one steered analog beam. 
     A beamforming system comprises an electronic inverse channelizer unit including a polyphase decimating finite impulse response (FIR) filter array configured to output a first plurality of up-sampled baseband channels. At least one electronic Fourier transform unit is configured to convert the first plurality of up-sampled baseband channels into a second plurality of real output signals. An electronic commutator unit is configured to generate a single radio frequency (RF) output signal in response to combining the second plurality of real output signals. 
     Additional features are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts: 
         FIG.  1    is a schematic diagram of a beamforming system according to an exemplary embodiment; 
         FIG.  2    is a schematic diagram of a channelizer included in a beamforming system according to an exemplary embodiment; 
         FIGS.  3 A- 3 B  are signal diagrams illustrating exemplary frequency responses of a channelizer illustrated in  FIG.  2    according to an embodiment; 
         FIG.  4    is a schematic diagram of a beamforming system according to another exemplary embodiment; 
         FIG.  5    is a schematic diagram of a beamforming system according to yet another exemplary embodiment; 
         FIG.  6    is a flow diagram illustrating a method of beamforming an RF signal according to an exemplary embodiment; and 
         FIG.  7    is a schematic diagram of an inverse channelizer to transmit an input signal from a number of baseband I/Q channel inputs according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It is noted that various connections are set forth between elements in the following description and in the drawings (the contents of which are included in this disclosure by way of reference). It is noted that these connections in general and, unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. In this respect, a coupling between entities may refer to either a direct or an indirect connection. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module, unit and/or element can be formed as processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     With reference now to  FIG.  1   , a beamforming system  100  is illustrated according to a non-limiting embodiment. According to an embodiment, the beamforming system  100  is interposed between an element array  102  and an electronic processing module  104  such as, for example, a field programmable gate array (FPGA)  104 . Although a FPGA  104  is described going forward, it is appreciated that any programmable device may be used. The element array  102  may include a single antenna, or a plurality of individual antennas. One or more transceiver/receiver filter modules  106  are interposed between the element array  102  and the beamforming system  100  to filter an incoming radio frequency (RF) signal. The transceiver/receiver filter modules  106  can also include circulator elements, low noise amplifiers, and/or power amplifiers as understood by one of ordinary skill in the art. According to a non-limiting embodiment, the incoming RF signal has a frequency ranging from approximately 2 gigahertz (GHz) to approximately 12 GHz. One or more signal converter units  108  such as, for example, analog-to-digital converters (ADCs), are interposed between the beamforming system  100  and the FPGA  104  to convert a steered analog beam into a digital signal. Although an application for signal reception is described going forward, it is appreciated that the beamforming system  100  can also be utilized for transmission applications. In transmission applications, it is appreciated that the signal converter units  108  are digital-to-analog converters (DACs). 
     The beamforming system  100  includes a plurality of electronic channelizers  110  and an electronic channel switching module  112 . Each channelizer  110  is configured to receive a respective RF signal  114  relayed by the element array  102  and generate a plurality of respective channels  116  in response to downsampling the respective RF signal  114 . It is appreciated that an electronic commutator unit (not shown) can be disposed upstream from the channelizers  110  at the first stage. According to a non-limiting embodiment, each channelizer  110  generates four channels configured to deliver a downsampled signal having a frequency ranging from approximately 0 GHz to approximately 3.25 GHz. 
     The channel switching module  112  is in signal communication with the plurality of channelizers  110  and is disposed upstream from the signal converter units  108 . The channel switching module  112  includes a channel combining circuit  118  and one or more pass-through circuits  120 . The channel combining circuit  118  includes a plurality of summer units  122  configured to selectively combine a common channel  116  such as, for example channel  1 , generated by each channelizer  110  to form at least one steered analog beam. The steered analog beam is then delivered to an output  117  and is received by a respective signal converter  108 . 
     According to an embodiment, one or more beam weight units  124  are interposed between a respective channel  116  and the channel combining circuit  118 . The beam weight units  124  apply a beam weight such as, for example a phase-shift, to the respective channel  116 . The combination of respective beam weights adjusts a direction of a respective steered analog beam delivered to the output  117 . One or more beams can also be steered by applying a true time delay within the channelizer. A combination of true time delay and beam weights such as, for example, phase shifts implemented as complex multiplies, can also steer one or more of the beams. In this manner, the channel switching module  112  can dynamically reconfigure at least one of a bandwidth of a respective beam and a number of total beams output from the channel combining circuit  118 . 
     The pass-through circuits  120  are interposed between a respective channel  116  and a respective output  117 . The pass-through circuit  120  forms a pass-through channel that selectively bypasses the channel combining circuit  112 . The pass-through channel can be established either manually and/or automatically. In this manner, a low frequency output (e.g., an output having a frequency ranging, for example, from 0 GHz to approximately 3.25 GHz) of one or more of the channelizers  110  can be connected to the pass-through circuit  120  and delivered directly to the FPGA  104  where it is digitized. The pass-through circuit  120 , however, is not limited to only low frequencies, and can be utilized any time it is desirable to combine one or more beams after digitization via the FPGA  104 . According to a non-limiting embodiment, for example, the frequency of one or more channels  116  is compared to a frequency threshold. When the frequency of a channel  116  is below the frequency threshold, a low frequency channel is determined and the pass-through circuit  120  establishes the pass-through channel. In this manner, the low frequency channel bypasses the channel combining circuit  112  and is automatically delivered to the FPGA  104  for processing. 
     As mentioned above, it is appreciated that the beamforming system  100  can also be utilized for transmission applications. In transmission applications, it is appreciated that the signal converter units  108  are digital-to-analog converters (DACs). 
     Turning to  FIG.  2   , a channelizer  110  included in the beamforming system  100  is illustrated according to a non-limiting embodiment. The channelizer  110  includes a filter unit  200  and one or more Fourier transfer units  202 . The filter unit  200  includes, for example, a polyphase decimating finite impulse response (FIR) filter array which is configured to downsample an input RF signal  114  into a plurality of polyphase lanes  204  for shaping the filter response. Although the filter unit  200  is shown as outputting eight polyphase lanes  204 , more or less polyphase lanes  204  may be output based on the desired application. The filter unit  200  is also configured to program a true time delay into one or more of the channels  116  generated by the channelizer  110 . According to an embodiment, a number of taps corresponding to the FIR filter  200  in one or more of the channelizers  110  is dynamically reconfigurable. For example, the taps of the FIR filter  200  can be dynamically reconfigured to provide 48 filter taps, 64 filter taps, or 128 filter taps per channelizer  110 . 
     The Fourier transform unit  202  executes a Fourier transform algorithm that aligns the output frequency domain signals to determine the portion of the frequency spectrum that is represented at baseband. In this manner, the output of the filter unit  200  is brought to baseband to generate the respective channels  116  output by the channelizer  110 . The Fourier transform unit  202  can apply various Fourier transform algorithms to the signals received from a respective filter unit including, but not limited to, a discrete Fourier transform (DFT) algorithm and a fast Fourier transform (FFT) algorithm. The multiplier weights of the Fourier transform can be set such that the nyquist zone of choice is coherently combined and other nyquist zones are non-coherently combined. In this manner, a selected nyquist zone of choice is represented at base band. According to an exemplary embodiment, the channelizer  110  can be programed to allocate a spectrum across a frequency band of a respective channel  116 . The frequency band can range, for example, from approximately 2 GHz to approximately 12 GHz. Although the channelizer  110  illustrated in  FIG.  2    is shown as comprising four Fourier transform units  202 , it is appreciated that the channelizer  110  may include more or less Fourier transfer units  202  to generate a particular number of channels  116  for a desired application. 
     Referring to  FIGS.  3 A- 3 B , signal diagrams illustrating dynamic adjustment of a polyphase filter response provided by a channelizer  110  included in the beamforming system  100  is illustrated according to a non-limiting embodiment. According to an embodiment, a polyphase filter Fourier transform algorithm can be used to generate a response equivalent to a down-mixed bandpass filter response. As shown in  FIG.  3 A , for example, an overlapping narrow response is illustrated when the Fourier transfer units  202  are controlled to select a plurality of closely-adjacent channels such as, for example, the first four channels among eight total channels. In  FIG.  3 B , however, a non-overlapping wide filter response is illustrated when the Fourier transfer unit  202  is controlled to select a plurality of alternating channels such as, for example, every other channel among the eight total channels generated by the channelizer  110 . 
     Turning to  FIG.  4   , another example of a beamforming system  100  is illustrated according to a non-limiting embodiment. The beamforming system  100  operates in a similar manner as described in detail above. According to an embodiment, the beam weight units  124   a - 124   d  apply different weights such as, for example, different phase-shifts, with respect to one another. For example, beam weight unit  124   a  applies a first weight to a respective input channel, beam weight unit  124   b  applies a second weight to a respective input channel, beam weight unit  124   c  applies a third weight to a respective input channel, and beam weight unit  124   d  applies a fourth weight to a respective input channel. 
     One or more common channels  116  of each channelizer  110   a - 110   d  are tapped upstream from the beam weight units  124   a - 124   d . According to an exemplary embodiment, a first channel (e.g., channel  1 ) common among each channelizer  110   a - 110   d  is tapped at a first point upstream from the beam weight units  124   a - 124   d  to generate a first channel set. The first channel set is delivered to a first beam weight unit such as, for example, unit  124   a , which applies a first beam weight to the first channel set. The weighted outputs  125   a  from the first beam weight unit  124   a  are delivered to a first summer such as, for example, summer  122   a , which combines the weighted outputs  125   a  to form a first common channel beam  127   a  that is steered in a first direction. 
     The first common channel is also tapped at a second point upstream from the beam weight units  124   a - 124   d  to generate a second channel set. According to an embodiment, the second channel set is generated simultaneously with the first channel set. The second channel set is output to a second beam weight unit such as, for example, unit  124   d , which applies a second beam weight different from the first beam weight. The second set of weighted outputs  125   d  from the second beam weight unit  124   d  is delivered to a second summer such as, for example, summer  122   d , which combines the weighted outputs  125   d  to form a second common channel beam  127   d  that is steered in a second direction different from the first direction of the first common channel beam  127   a . Accordingly, a set of common channels from each channelizer  110   a - 110   d  is tapped and applied with different beam weights to simultaneously produce multiple beams (e.g.,  127   a ,  127   d ) steered in different directions with respect to one another. 
     Referring now to  FIG.  5   , another example of a beamforming system  100  is illustrated according to a non-limiting embodiment. The beamforming system  100  operates in a similar manner as described in detail above. The beamforming system  100  shown in  FIG.  5   , however, includes a beam combiner  126  interposed between the output of the channel combining circuit  118  and the signal converter  108 . Each summer  122   a - 122   d  of the channel combining circuit  118  can selectively output a respective channel beam  117   a - 117   d . For example, a first summer  122   a  outputs a first channel beam  117   a  (i.e., a beam formed by combing one or more first channels  116   a  (e.g., channel  1 ) having a frequency ranging, for example, from approximately 0 GHz to approximately 3 GHz. A second summer  122   b  outputs a second channel beam  117   b  (i.e., a beam formed by combing one or more second channels  116   b  (e.g., channel  2 ) having a frequency ranging from approximately 3 GHz to approximately 6 GHz. The beam combiner  126  combines two or more individual channel beams output from a respective summer  122   a - 122   d  (e.g., the first channel beam  117   a  and the second channel beam  117   b ) to form a single combined beam  128  that is multiple channels wide. Although the combined beam  128  is generated in response to combining beam  117   a  from summer  122   a  and beam  117   b  output from summer  122   b , it is appreciated that the beamforming system  100  is configured to combine any grouping of beams output from the summers  122   a - 122   d  to generate the single combined beam  128 . 
     Turning now  FIG.  6   , a flow diagram illustrates a method of beamforming a radio frequency signal according to a non-limiting embodiment. The method begins at operation  600 , and at operation  602 , an incoming RF signal is downsampled. The downsampled signals are utilized to generate a plurality of polyphase lanes at operation  604 . At operation  606 , a plurality of channel sets are generated based on the polyphase lanes. Each channel set includes a plurality of channels. At operation  608 , selected channels from one or more of the channel sets are combined to form at least one steered analog beam, and the method ends at operation  610 . It is appreciated that any embodiment of the present invention including, but not limited to, the beamforming systems described with referenced to  FIGS.  1 ,  4  and  5   , can implement the method of  FIG.  6   . 
     Referring now to  FIG.  7   , an inverse channelizer  700  is illustrated according to a non-limiting embodiment. The inverse channelizer  700  is configured to process one or more input signals, such as a complex RF input signal (I, Q) for example, from a number of baseband channel inputs to generate a steered output RF signal  702 . 
     The inverse channelizer  700  includes a filter unit  704  and  706  and one or more Fourier transform units  708 . The filter unit  704  such as, for example, a polyphase decimating finite impulse response (FIR) filter array, is configured to convert a plurality of polyphase signals into one or more up-sampled baseband channels (e.g., I/Q channels). The baseband channels are routed to a plurality of FIR filter branches  706  which are in signal communication with the Fourier transfer units  708 . The branches  706  can be dynamically tapped to dynamically reconfigure the filter unit  704 . The Fourier transform units  708  take in one or more baseband channels such as, for example, I/Q odd channels  710   a  and I/Q even channels  712   a , and generate a number of real signal outputs  714 . For example, two I input signals  710   a  and two Q signals  712   a  are combined to produce a real output  714   a , such that from sixteen I/Q channels  710   a - 710   p / 712   a - 712   p , eight real channels  714   a - 714   h  are formed. 
     The outputs  714   a - 714   h  are delivered to an electronic commutator unit  716  which samples one or more of the real output signals  714   a - 714   h . For example, a first channel  714   a  is output on a first clock cycle, a second sample is output on a second clock cycle, etc. According to an embodiment, the commutator unit  706  receives eight real channels  714   a - 714   h  from the Fourier transfer units  706 . The real channels  714   a - 714   h  are up-sampled and are clocked at 3.25 GHz rate, for example. The commutator unit  706  combines the real channels  714   a - 714   h  to form a single output signal  702  that is clocked at, for example, 26 GHz. According to the non-limiting embodiment illustrated in  FIG.  7   , the FIR filter unit  704  and the Fourier transform units  708  are all clocked at 3.25 GHz, for example, and the commutator unit  716  is clocked at, for example, 26 GHz. 
     The inverse channelizer  700  of  FIG.  7    and channelizers  100  of  FIGS.  1 ,  4  and  5    have similar operations. The inverse channelizer  700 , however, includes the electronic commutator unit  716  disposed as the last stage. Thus, the inverse channelizer  700  converts eight real channel inputs  714   a - 714   h  into a single RF output  702  whereas the channelizer  100  includes a commutator disposed in the first stage which receives a single real input signal and produces eight channels, for example. It is appreciated that any number of input channels can be used. Accordingly, if the inverse channelizer allows four sets of complex input channels and data is only provided through one of the channels, the other remaining channels can be “grounded” and left unused. A number of digital to analog converters can be included to provide the inputs to these complex baseband channels into the inverse channelizer. According to an embodiment, a channelizer  100  can be in signal communication with the inverse channelizer  700 . In this manner, common nodes can be formed such that the FIR filter unit  704  of the inverse channelizer can re-use circuit blocks from the channelizer  100 . 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     While the preferred embodiments to the invention have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.