Abstract:
The programmable wide-band radio frequency feed network is a wideband multi-port microwave/RF feed network that can operate with multiple communication bands covering a wide frequency range. In addition, the feed network is programmable via a digital controller and has two degrees of freedom, viz., amplitude and phase variations. The feed network provides amplification as well as attenuation to the amplitude of the incoming signals. The feed network is designed using discrete microwave components, and fabricated on a multilayer printed circuit board (PCB) with a small footprint. The digitally controlled feed network is ideal for any antenna array application within the covered frequency range, and can be re-programmed for various wireless communication standards.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to control electronics for phased array antenna systems, and particularly to a programmable wide-band radio frequency feed network adapted for a phased array antenna system that uses multiple antenna elements or multiple RF paths to optimize signal transmission and reception. 
         [0003]    2. Description of the Related Art 
         [0004]    Antenna arrays rely on microwave or radio frequency (RF) feed networks to provide the appropriate excitations for the array to function according to its design specifications. The excitations of the various elements of the antenna array are provided to steer the beam in a certain direction to enhance the communication link (thus beam steering) or create nulls in the radiation pattern of the array to eliminate interference (thus null steering). 
         [0005]    There are two degrees of freedom that are usually utilized in the design of microwave feed networks, the amplitude and the phase. The different paths within the feed network are given certain amplitude and phase excitations relative to the center path or one of the edge paths. In most applications, the feed network is fixed and engraved within the hardware of the system or antenna structure, operating at a certain narrow frequency band. Thus, it is optimized to work for that application only and cannot be altered once the design is taped out (fabricated). In other designs, the feed network for that application has one degree of freedom (such as the phase excitations, e.g., those in smart antenna systems with phased arrays, or amplitude excitations). Although the most common design is the one that uses phase changes as the degree of freedom in phased array implementations (because it is convenient to control the phases by either voltage controlled devices or by altering the lengths of the feed lines), amplitude variations are also utilized via the use of variable gain amplifiers. 
         [0006]    While there are some designs where the feed network has both phase and amplitude variations, the architectures that appear in the literature are only meant for a specific band of frequencies and cannot be used for others. In addition, most of them cover a limited number of frequency bands. For system level engineers, there is no generic architecture that they can use for rapid prototyping of their antenna array designs, where they do not need to worry about the feed network as an integral part of their antenna array design. 
         [0007]    Thus, a programmable wide-band radio frequency feed network solving the aforementioned problems is desired. 
       SUMMARY OF THE INVENTION 
       [0008]    The programmable wide-band radio frequency feed network is a wide-band, multi-port microwave/RF feed network that can operate with multiple communication bands covering a wide frequency range. The feed network is programmable via a digital controller and has two degrees of freedom, viz., amplitude and phase variations. The feed network provides amplification, as well as attenuation, to the amplitude of the incoming signals. The feed network is designed using discrete microwave components, and fabricated on a multilayer printed circuit board (PCB) with a small footprint. The digitally controlled feed network is ideal for any antenna array application within the covered frequency range and has a programming port from which it can be re-programmed for various wireless communication standards. As used herein, the term wide-band means about 4 GHz. 
         [0009]    These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram of a radio transceiver having a phased array antenna that uses a programmable wide-band radio frequency feed network according to the present invention to interface a transceiver (or transmitter or receiver) to the antenna. 
           [0011]      FIG. 2  is a block diagram of an embodiment of a programmable wide-band radio frequency feed network according to the present invention configured for a transmitter. 
           [0012]      FIG. 3  is a block diagram of an embodiment of a programmable wide-band radio frequency feed network according to the present invention configured for a receiver, 
           [0013]      FIG. 4  is a block diagram of an alternative embodiment of a programmable wide-band radio frequency feed network according to the present invention configured for a transceiver, or for both a transmitter and a receiver. 
           [0014]      FIG. 5  is a block diagram of the user interface portions of a programmable wide-band radio frequency feed network according to the present invention. 
           [0015]      FIG. 6  is a block diagram of a programmable wide-band radio frequency feed network according to the present invention configured with an RF combiner and a beamformer. 
           [0016]      FIG. 7A  is a plot showing the RF gain level as a function of frequency for a model of the programmable wide-band radio frequency feed network configuration of  FIG. 3  from 2.0-3.5 GHz. 
           [0017]      FIG. 7B  is a plot showing the phase as a function of frequency for a model of the programmable wide-band radio frequency feed network configuration of  FIG. 3  from 2.0-3.5 GHz. 
           [0018]      FIG. 8A  is a plot showing the RF gain level as a function of frequency for a model of the programmable wide-band radio frequency feed network configuration of  FIG. 3  from 2.5-6.5 GHz. 
           [0019]      FIG. 8B  is a plot showing the phase as a function of frequency for a model of the programmable wide-band radio frequency feed network configuration of  FIG. 3  from 2.5-6.5 GHz. 
       
    
    
       [0020]    Similar reference characters denote corresponding features consistently throughout the attached drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The programmable wide-band radio frequency (RF) feed network is operational in a generic phased array antenna communication system, as shown in  FIG. 1 . Generally, each element of the phased array is configured for a corresponding phase of the RF signal and defines a corresponding RF path in the feed network. In the transmit mode of operation, the radio  12  (which may be a transceiver, a transmitter, or a receiver) sends the RF signals to the RF feed network  14  (or receives the signals from the network) via a single or multiple cable connectors  13 . The programmable wide-band radio frequency feed network  14  modifies the amplitudes and phases of the incoming signals for proper application to the antennas  11  for wireless transmission, or modifies the amplitudes and phases of the received signals for proper application to the radio (receiver or transceiver)  11  for reception. The output of the RF feed network  14  can be a single path feeding a single antenna, or multiple paths feeding multiple antennas. This is determined by the application under consideration. 
         [0022]      FIG. 2  shows a more detailed architecture of the digitally controlled, wide-band and programmable RF feed network  14  in the transmit mode (configured for use with a transmitter). The mode of operation that determines the amplitude and phase excitations for the different paths has to be set and programmed into a digitally programmed controller  29  via a programming cable  21 . These programmed amplitude and phase excitations are used to control the digitally programmed phase shifters  24 ,  31  and amplifiers  26  via control lines  224 ,  231  and  28 , respectively. In the transmit mode of operation, the digital controller  29  will be instructed to choose from two frequency ranges of operation, a low range and a high range. For the low range of frequency operation, the digital controller  29  chooses the bottom path of  FIG. 2  by sending control signals to the single pole double throw (SPDT) RF switch array  22  via control line  220  to connect the incoming RF signals received at inputs  23  to the low frequency range phase shifters  24  via a set of RF lines  30 . The phase shift values for the digitally controlled phase shifters  24  are determined by the digital controller  29  through the type of application stored for the feed network  14 . The signal is then passed to another SPDT RF switch array  25  to a bank of programmable amplifiers  26 . RF lines  30  are selected by the SPDT switch array  25  under control of digital controller  29 , which controls the SPDT switch array  25  via control line  250 . Signals carried by the selected RF lines are routed to inputs of selected amplifiers  26  according to the settings of the SPDT switch array  25 . The signals undergo amplitude adjustment in the amplifiers  26  under control of the digital controller  29 , which also sets the gain of each amplifier  26  via amplitude control lines  28 . The RF output is then sent to the output ports  27 . 
         [0023]    For the high frequency range of operation, the incoming RF signals  23  are passed to the upper branch of  FIG. 2  via the SPDT RF switch array  22 . It is then passed to the digitally controlled phase shifters  31  through a set of RF cables  30 . The outputs of the shifters are passed to the second SPDT RF switch array  25 , and then to the bank of digitally controlled amplifiers  26  for amplitude adjustments. The amplifier outputs are then passed to the output RF lines  27 . This architecture can work with any number of input/output signals and can have more than two paths if required by the frequency ranges to be covered. 
         [0024]      FIG. 3  shows the architecture for the receive mode of operation. The program that defines the amplitude and phase levels for the application considered is transferred and stored into the digital controller  46  via the programming cable  43 . RF signals coming from multiple antennas are passed to the inputs  48  of the digitally controlled feed network. The signals are then passed to the amplifier bank  49 . Control signals are sent via control lines  47  from the digital controller  46  to the amplifiers to set gains of amplifier bank  49  to the appropriate levels. After having their levels adjusted, the RF signals are passed to the SPDT switch array  50  to be sorted or routed to the correct phase path as determined by the digital controller  46 , which controls the SPDT array  50  via control line  346 . The RF signals are passed to the low band digitally controlled phase shifters  51  and the high band digitally controlled phase shifters  44  via the RF lines  45 , The digital controller  46  adjusts the low band phase shifters  51  via low band control lines  351  and adjusts the high band phase shifters  44  via high band control lines  344 . The system also may accommodate any number of paths. Thus, more than two paths can be provided, if the switch arrays  42  and  50  are adjusted accordingly. The controller  46  also controls the SPDT switch array  42  via control line  342 . After phase adjustments, the signals are passed to the output SPDT switch array  42 , and then to the feed network output ports  41 , which are connected to the radio receiver  12 . 
         [0025]    Another configuration that will provide a digitally controlled and wide-band feed network in transceiver architecture (or a discrete transmitter and a discrete transmitter, the feed network having transmitter and receiver modes in one design) is shown in  FIG. 4 . The program that determines the mode of operation is loaded on the digital controller  66  via the programming cable  63 . The feed network can now be used alternately in receive mode or in transmit mode. The amplifier bank, including the transmit amplifiers  69  and the receive amplifiers  70 , is switched according to the desired mode via the amplifier control cables  67  coming from the digital controller  66 . The RF signals received by the antennas come into the network at ports  68  will be passed to the receiver amplifier bank  70  and then to the SPDT switch array  72 . The SPDT switch array  72  is set by digital controller  66  via control line  472  to the proper RF path over RF lines  65  either to the low frequency phase shifters  71  or to the high frequency phase shifters  64 . The controller  29  adjusts the RF signal phases via control lines  464  (to the high frequency phase shifters  64 ) and  471  (to the low frequency phase shifters). After phase shifting, the RF signals are then passed to the second SPDT switch array  62  to the selected ports  61  leading to the radio  12 . If the transmit mode is chosen, the input signal from ports  61  goes through the appropriate path according to the frequency band of interest, and then gets out of the feed network after having their levels adjusted by the transmit amplifier bank  69 . The SPDT switch array  62  is controlled by the digital controller  66  via control line  462 . 
         [0026]    The digital controller interface can have the configuration shown in the diagram of  FIG. 5 . The program to be loaded is sent to the digital controller  513  via the programming cable  511 . The program can prompt the user to choose from different options via the input keys  514 , and displays the modes and results on the display  512 . This also covers any alternative of this architecture that includes a digital controller, input keys, display and programming cable. 
         [0027]    The programmable wide-band radio frequency feed network can be used in different configurations, such as the beamforming antenna array architecture shown in  FIG. 6 . A conventional beamformer  616  programmed to execute any conventional beam forming algorithm is used to update the amplitudes and phases of the digitally programmed feed network  614  via a programming cable  615 . The beamforming algorithm gets its inputs dynamically from the output of the feed network via cables  617  and feeds back adjustments in the phases and amplitudes for a dynamic mode of operation that is in real time. The incoming signals from the antenna array  613  are passed through the RF feed network  614 , where the amplitudes and phases are adjusted and then passed to an RF combiner circuit  611  that provides a single RF output  612  to the radio receiver. 
         [0028]      FIGS. 7A-7B  show results of a model based on the configuration in  FIG. 3 . Plot  700  of  FIG. 7A  shows gain level obtained in the lower frequency branch covering 2.0-3.5 GHz. The results are based on measured s-parameter values of individual components within the feed network path. The phase shift set on the programmable phase shifters  51  was 95.625 degrees and the gain of amplifier  49  was set to its maximum level of 18 dB. The phase shift plot  710  obtained across this low band of operation is shown in  FIG. 7B . 
         [0029]      FIGS. 8A-8B  show results of a model based on the configuration in  FIG. 3 .  FIG. 8A  shows a plot  800  of gain level obtained in the higher frequency branch covering 2.5-6.5 GHz. The results are based on measured s-parameter values of individual components within the feed network path. The phase shift set on the programmable phase shifters  44  was 95.625 degrees and the gain of amplifier  49  was set to its maximum level of 18 dB. The phase shift plot  810  obtained across this high band of operation is shown in  FIG. 8B . 
         [0030]    The programmable wide-band radio frequency feed network may have different variations and combinations, and may have any number of paths based on the number of frequency bands to be covered, as well as any number of RF input/output ports. The architecture is programmable, and can be customized according to the application to be considered. 
         [0031]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.