Patent Publication Number: US-2023163865-A1

Title: Time-division duplex (tdd) antenna system

Description:
TECHNICAL FIELD 
     This disclosure relates generally to communication systems, and more specifically to a time-division duplex (TDD) antenna system. 
     BACKGROUND 
     An antenna array (or array antenna) is a set of multiple antenna elements that work together as a single antenna to transmit or receive radio waves. The individual antenna elements can be connected to a receiver and/or transmitter by circuitry that applies an appropriate amplitude and/or phase adjustment of signals received and/or transmitted by the antenna elements. When used for transmitting, the radio waves radiated by each individual antenna element combine and superpose with each other, adding together (interfering constructively) to enhance the power radiated in desired directions, and cancelling (interfering destructively) to reduce the power radiated in other directions. Similarly, when used for receiving, the separate received signals from the individual antenna elements are combined with the appropriate amplitude and/or phase relationship to enhance signals received from the desired directions and cancel signals from undesired directions. 
     SUMMARY 
     One example includes a self-synchronizing TDD antenna system. The system includes an antenna system to communicate transmit and receive signals and an antenna control circuit coupled to a user communication system. The antenna control circuit includes a transmission line measurement circuit to determine signal loss through a transmission line cable coupled to the antenna system and an amplitude adjustment circuit to adjust amplitude of the transmit and/or receive signals based on the signal loss. A transmit detection circuit monitors signal power of the transmit signal, and a controller switches the amplitude adjustment circuit from a receive mode to a transmit mode in response to the monitored signal power exceeding a predetermined threshold. In the receive mode, the adjustment circuit applies a receive amplitude adjustment to the receive signal, and in the transmit mode the adjustment circuit applies a transmit amplitude adjustment to the transmit signal. 
     Another example includes a method for communicating at least one of a transmit signal and a receive signal via a time-division duplex (TDD) antenna communication system comprising an antenna system. The method includes providing a calibration signal from an antenna control circuit to the antenna system on at least one transmission line cable and receiving a returned signal corresponding to the calibration signal retransmitted back from the antenna system to the antenna control circuit on the at least one transmission line cable. The method also includes determining signal loss between the antenna system and the antenna control circuit through the at least one transmission line cable based on the returned signal and adjusting an amplitude of the receive signal received via the at least one transmission line cable in the receive mode based on the determined signal loss. The method also includes monitoring signal power of the transmit signal obtained from the user communication system and switching an amplitude adjustment circuit from the receive mode to a transmit mode in response to the monitored signal power exceeding a predetermined threshold. The method further includes adjusting an amplitude of the transmit signal in the transmit mode based on the determined signal loss. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of a communication system. 
         FIG.  2    illustrates an example of an antenna control circuit. 
         FIG.  3    illustrates an example diagram of calibration of a communication system. 
         FIG.  4    illustrates another example diagram of calibration of a communication system. 
         FIG.  5    illustrates an example of a calibration circuit. 
         FIG.  6    illustrates another example of a calibration circuit. 
         FIG.  7    illustrates an example of a transmission line measurement circuit. 
         FIG.  8    illustrates an example of a controller. 
         FIG.  9    illustrates an example of a TDD communication stream. 
         FIG.  10    illustrates an example of an amplitude adjustment circuit. 
         FIG.  11    illustrates another example of an amplitude adjustment circuit. 
         FIG.  12    illustrates another example of an amplitude adjustment circuit. 
         FIG.  13    illustrates another example of an amplitude adjustment circuit. 
         FIG.  14    illustrates another example of an amplitude adjustment circuit. 
         FIG.  15    illustrates another example of an amplitude adjustment circuit. 
         FIG.  16    illustrates an example of a method for communicating at least one of a transmit signal and a receive signal via a time-division duplex (TDD) antenna system comprising an antenna. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates generally to communication systems, and more specifically to a time-division duplex (TDD) antenna system. A communication system can be implemented that includes a user communication system and an antenna system. As an example, the communication system can he implemented as a wireless broadband communication system, such as using a Long Term Evolution (LTE) communication standard. The antenna system can be physically communicatively coupled (e.g., via a set of transmission line cable) to an antenna control circuit that is coupled to the user communication system to provide enhanced wireless communication capability for the communication system, such as to provide wireless extension or capability of the user communication system to communicate with a base station (e.g., in a time-division duplex (TDD) manner). For example, the antenna system can provide wireless communication capability for the user communication system based on the user communication system being located in a location that prohibits or impedes wireless connection to a base station based on, for example, intervening physical barriers or extreme range. 
     The antenna system includes one or more antenna arrays and a calibration circuit. The antenna array(s) can be arranged as any of a variety of antenna arrays to provide a respective one or more wireless signals to be transmitted from and/or received at the antenna system. For example, the antenna array(s) can include an arrangement of antenna elements (e.g., strip-line conductors) to provide signal diversity between two or more respective signal paths, such as based on polarization diversity (e.g., orthogonal polarizations of two separate signal paths), The antenna array(s) can thus each transmit signal(s) and receive signal(s), such as in a TDD manner based on a defined standard on which the user communication system operates. 
     As described herein, the antenna control circuit can determine cable losses of the interconnection between the antenna system and the user communication system, such as in a calibration procedure. As a result, the antenna control circuit can be implemented to provide attenuation of transmitted signals (hereinafter “transmit signals”) provided from the user communication system via the antenna array(s) in a manner that allows the transmit signals be transmitted at or below a predetermined effective isotropic radiated power (EIRP), such as defined by the operating standard of the user communication system. Additionally, as also described herein, the antenna control circuit can be configured to monitor signal power on the respective communication paths to facilitate the TDD operation of the communication system without any input from the user communication system. As a result, the antenna system can be installed to cooperate with the user communication system in a manner that is substantially agnostic of the interconnection between the antenna control circuit and the antenna system, and without active communication between the antenna system and the user communication system. 
       FIG.  1    illustrates an example of a communication system  10 . The communication system  10  can be implemented as a wireless broadband communication system, such as using a Long Term Evolution (LTE) communication standard. In the example of  FIG.  1   , the communication system  10  includes a user communication system  12 , an antenna control circuit  13 , and an antenna system  14 . As an example, the user communication system  12  can correspond to a wireless gateway, such as to facilitate wireless communications (e.g., Wi-Fi, Bluetooth, and/or cellular communication) between one or more user devices and a wireless network, such as a cellular network or other wide-area network (WAN). 
     In the example of  FIG.  1   , the antenna system  14  is communicatively coupled to an antenna control circuit  13  via at least one transmission line cable  16  (e.g., an RG6 cable), such that the antenna control circuit  13  interconnects the user communication system  12  (e.g., via additional transmission line cable(s)) and the antenna system  14 . As an example, the antenna. system  14  can provide enhanced wireless communication capability for the user communication system  12 , such as to provide wireless extension or capability of the user communication system  12  to communicate with a base station (e.g., in a time--division duplex (TDD) manner) For example, the antenna system  14  can provide wireless communication capability for the user communication system  12  based on the user communication system  12  being located in a location that prohibits or impedes wireless connection to a base station based on, for example, intervening physical harriers or extreme range. 
     The antenna system  14  includes one or more antenna arrays  18  and a calibration circuit  20 . The antenna array(s)  18  can be arranged as any of a variety of antenna arrays to provide a respective one or more wireless signals to be transmitted from and/or received at the antenna system  14 . For example, the antenna array(s)  18  can include an arrangement of antenna elements (e.g., strip-line conductors) to provide signal diversity between two or more respective signal paths, such as based on polarization diversity. For example, the antenna array(s)  18  can include two separate arrays of orthogonally polarized antenna elements to provide orthogonal polarizations of signals propagating in two separate respective signal paths between the user communication system  12  and the antenna system  14  through the antenna control circuit  13 . The antenna array(s)  18  can thus each transmit signal(s) and receive signal(s), such as bidirectionally in a TDD manner based on a defined standard on which the user communication system  12  operates. In the example of  FIG.  1   , signals transmitted from and received at the antenna array(s)  18  are demonstrated as signals “RF”, and the same signals propagating bidirectionally along the transmission line cable(s)  16  are demonstrated as signals “TS”. 
     The antenna control circuit  13  includes a transmission line measurement circuit  22  and an amplitude adjustment circuit  24 . The transmission line measurement circuit  22  is configured to determine a signal loss between the antenna system  14  and the antenna control circuit  13  through the at least one transmission line cable  16 . For example, during installation of the antenna system  14  and/or periodically thereafter, the transmission line measurement circuit  22  can initiate a calibration operation (e.g., in response to a calibration command). As an example, during the calibration operation, the transmission line measurement circuit  22  can be configured to generate a calibration signal, such as a radio frequency (RF) signal, that can be transmitted to the antenna system  14  from the antenna control circuit  13  via the transmission line cable(s)  16 , such that the calibration signal can be retransmitted back to the antenna control circuit  13  from the antenna system  14  via the transmission line cable(s)  16 . As a result, the transmission line measurement circuit  22  can measure at least one characteristic of the return signal (e.g., power) to determine signal loss exhibited by the transmission line cable(s)  16 . 
     In response to determining the signal loss, the amplitude adjustment circuit  24  can be configured to adjust an amplitude of at least one of transmit signals transmitted from the antenna system  14  and receive signals received at the antenna, system  14  based on the determined signal loss. As described herein, the term “transmit signals” refers to signals that are originated at the user communication system  12 , propagate through the transmission line cable(s)  16  as a signal TS, and are transmitted from the antenna system  14  via the antenna array(s)  18  as a signal RF. Similarly, the term “receive signals” refers to signals that are received at the antenna system  14  via the antenna array(s)  18  as a signal RF, propagate through the transmission line cable(s)  16  as a signal TS, and are provided to the user communication system  12 . The amplitude adjustment circuit  24  can therefore adjust the amplitude of the transmit and receive signals in separate respective signal paths in the antenna control circuit  13  based on the signal loss determined during the calibration operation. 
     For example, the communication system  10  can be configured to operate based on a predetermined communication standard that can dictate a predetermined maximum effective isotropic radiated power (EIRP), such as +23 dBm for the transmit signals. As an example, the amplitude adjustment circuit  24  can include one or more variable circuit elements (VCEs) to amplify or attenuate the transmit signals (e.g., down to less than the predetermined maximum EIRP) and/or the receive signals (e.g., down to less than a maximum saturation power associated with the antenna control circuit  13  and/or the user communication system  12 ). For example, the antenna array(s)  18  can be designed with sufficient gain, or the antenna control circuit  13  can be sufficiently high gain to provide the transmit signals at a power level that is greater than the predetermined maximum EIRP (e.g., to overcome power losses of the transmission line cable(s)  16  regardless of the length of the transmission line cable(s)  16 ), such that the transmit signals can be attenuated down to approximately the predetermined maximum EIRP. Therefore, the antenna system  14  can be installed in a manner that is substantially agnostic of the length and/or loss characteristics of the transmission line cable(s)  16  based on the calibration operation to determine the signal loss of the transmission line cable(s)  16 . 
     In the example of  FIG.  1   , the antenna control circuit  13  also includes a transmit detection circuit  26  and a controller  28 . As described previously, the communication system  10  can operate based on a TDD communication standard, such that the transmit signals and the receive signals can be interleaved with each other on a given signal path between the user communication system  12  and the antenna array(s)  18 . The transmit detection circuit  26  can be configured to measure power on a given signal path in the antenna control circuit  13  to determine if user communication system  12  is transmitting a transmit signal. Therefore, in response to determining if the user communication system  12  is transmitting a transmit signal, the controller  28  can switch the adjustment circuit  24  from a receive mode (e.g., as a default mode) to a transmit mode to facilitate transmission of the transmit signal from the antenna system  14  via the antenna array(s)  18 . Additionally, in response to the transmit detection circuit  26  detecting a decrease in the power of the signal path (e.g., less than the predetermined threshold), the controller  28  can switch the adjustment circuit  24  back to the receive mode from the transmit mode (e.g., upon expiration of a timer). 
     In response to the transmit detection circuit  26  determining that the user communication system  12  is transmitting a transmit signal, such as based on the power on the signal path being greater than a predetermined threshold, the controller  28  can provide a signal to the amplitude adjustment circuit  24  to switch the signal path from a receive mode to a transmit mode. Therefore, the amplitude adjustment circuit  24  can provide the appropriate amplitude adjustment to the transmit signal (e.g., via a VCE) to facilitate transmission of the transmit signal from the antenna system  14  via the antenna array(s)  18 . As an example, the amplitude adjustment circuit  24  can include power amplifier and/or a filter in each of the transmit and receive switchable portions of the signal path, and/or can include a short-circuit bypass path in one of the transmit and receive signal paths. 
     As a result, the antenna system  14  can operate to facilitate the bidirectional TDD communications between transmit and receive signals without requiring communication or signal transfer from the user communication system  12 . Therefore, the antenna system  14  can be installed in a simplistic manner that is largely independent of the operation of the user communication system  12 . Additionally, as previously described, the antenna system  14  can be installed in a manner that is agnostic of the length of the transmission line cable(s)  16  interconnecting the antenna system  14  and the antenna control circuit  13 . Accordingly, and as described in greater detail herein, the antenna system  14  can be simplistically installed to efficiently facilitate wireless communication between the user communication system  12  and a network hub (e.g., a base station) 
       FIG.  2    illustrates an example of an antenna control circuit  50 . The antenna control circuit  50  can correspond to the antenna control circuit  13  in the example of  FIG.  1   . Therefore, reference is to be made to the example of  FIG.  1    in the following description of the example of  FIG.  2   . 
     The antenna control circuit  50  is demonstrated in the example of  FIG.  2    as including a first signal path  52  and a second signal path  54  that can each correspond to a separate signal diversity type, as described in greater detail herein. Additionally, the antenna control circuit  50  is communicatively coupled to the antenna system (e.g., the antenna system  14 ) via a first transmission line cable  56  configured to propagate a signal TS 1  between the antenna system and the antenna control circuit  50  and a second transmission line cable  58  configured to propagate a signal TS 2  between the antenna system and the antenna control circuit  50 . For example, the transmission line cables  56  and  58  can be connected to a calibration circuit (e.g., the calibration circuit  20 ) that is coupled to the antenna system. The transmission line cables  56  and  58  can each be associated with the respective signal diversity types, and thus the respective signal paths of the antenna control circuit  50 . For example, the transmission line cables  56  and  58  can be configured as RG6 cables or other types of transmission line cables. 
     In the example of  FIG.  2   , the antenna control circuit  50  includes a first amplitude adjustment circuit  60  that is provided in the first signal path  52  and a second amplitude adjustment circuit  62  that is provided in the second signal path  54 . As an example, the amplitude adjustment circuits  60  and  62  can each include at least one variable circuit element (VCE) in the respective signal paths  52  and  54 . For example, the VCEs can be configured as variable attenuators, variable gain amplifiers, and/or fixed gain amplifiers. As described in greater detail herein, the amplitude adjustment circuits  60  and  62  can provide amplification (e.g., attenuation) of the signals TS 1  and TS 2 . As described herein, the term “amplification” can refer to adjusting the signals TS 1  and TS 2  with a positive gain or a negative gain. As an example, the gain can be set to zero as a bypass condition (e.g., for receive signals TS 1  and TS 2 ). In the example of  FIG.  2   , the signals TS 1  and TS 2  are provided to the respective amplitude adjustment circuits  60  and  62  via through a first switch SW 1  and a second switch SW 2 , respectively. 
     In the example of  FIG.  2   , the antenna control circuit  50  includes a power block  64  interconnecting the amplitude adjustment circuits  60  and  62  and the transmission line cables  56  and  58 . The power block  64  is configured to generate or receive a DC voltage V DC . As an example, the voltage V DC  can have an amplitude that varies between a normal operating mode and a calibration mode. For example, the power block  64  can be configured as a low-dropout (LDO) voltage regulator, such as to generate the DC voltage V DC  from a higher input voltage. The power block  64  provides the DC voltage V DC  to a first injection circuit  66  and a second injection circuit  68 . For example, the injection circuits  66  and  68  can be configured as bias-tees. The injection circuits  66  and  68  are each coupled to the transmission line cables  56  and  58  on which the transmit and receive signals TS 1  and TS 2 , respectively, are propagated. Therefore, the injection circuits  66  and  68  are configured to provide the DC voltage V DC  onto the transmission line cables  56  and  58  to the antenna system for control of associated electronics (e.g., switches) in the antenna system. 
     The antenna control circuit  50  also includes a transmission line measurement circuit  70 . The transmission line measurement circuit  70  is configured to determine a signal loss between the user communication system and the antenna control circuit  50  through the transmission line cables  56  and  58 . For example, during installation of the associated antenna system and/or periodically thereafter, the transmission line measurement circuit  70  can initiate a calibration operation in response to a calibration command CAL. As an example, the calibration command CAL can be provided in response to a user input, such as via a physical input on the antenna control circuit  50  or the calibration system  20  (e.g., a physical button or a button on a touchscreen), in response to power-up of the antenna control circuit  50  (e.g., automatically in response to initially receiving the voltage V DC ), periodically from a processor or controller device (e.g., at periodic or programmable intervals), or from any of a variety of other means. As a further example, the calibration command CAL can be initiated in response to a change in the DC voltage V DC , or can be initiated via tone signaling on the signals TS 1  and TS 2 . 
     In the example of  FIG.  2   , the transmission line measurement circuit  70  includes a calibration signal generator  72 , a signal monitor  74 , and a memory  76 . The transmission line measurement circuit  70  is communicatively coupled to the first amplitude adjustment circuit  60  through the first switch SW 1  and to the second amplitude adjustment circuit  62  through the second switch SW 2 . In the example of  FIG.  2   , the switches SW 1  and SW 2  are demonstrated as being set to a normal operating mode state, and are controlled via the calibration command CAL. Therefore, in the normal operating mode, as in the state demonstrated in the example of  FIG.  2   , the switch SW 1  connects the first amplitude adjustment circuit  60  to the first signal path  52  to receive the signal TS 1 , and and the switch SW 2  connects the second amplitude adjustment circuit  62  to the second signal path  54  to receive the signal TS 2 . Therefore, in the normal operating mode, the switches SW 1  and SW 2  can facilitate propagation of the transmit and receive signals between the user communication system and the antenna system via the respective signal paths  52  and  54  and the respective transmission line cables  56  and  58 . However, in a calibration mode, such as initiated by the calibration command CAL, the switches SW 1  and SW 2  can be switched to coupling the amplitude adjustment circuits  60  and  62  to the transmission line measurement circuit  70  to facilitate the calibration operation. 
     During the calibration operation, the calibration signal generator  72  can be configured to generate a calibration. signal, such as a dummy RF signal having a predefined frequency. In the example of  FIG.  2   , the calibration signal is demonstrated as a first calibration signal CS 1  and a second calibration signal CS 2  corresponding, respectively, to the first and second transmission line cables  56  and  58  via the amplitude adjustment circuits  60  and  62 . The transmission line measurement circuit  70  can thus transmit one or both of the calibration signals CS 1  and CS 2  to the antenna system via the respective one of the transmission line cables  56  and  58 . 
     The antenna system can be configured to retransmit the calibration signal(s) CS 1  and/or CS 2  back to the antenna control circuit  50  from the antenna system as respective return signal(s) via the transmission line cables  56  and  58  during the calibration procedure. In response to receiving the return signal(s), the signal monitor  74  can be configured to measure at least one characteristic of the return signal(s) to determine signal loss exhibited by the transmission line cables  56  and  58 . For example, the characteristic of the return signal can be power, such that the signal monitor  74  can calculate a power ratio between one of the calibration signals CS 1  and CS 2  and the respective return signal. Accordingly, the signal monitor  74  can determine the signal loss exhibited by the transmission line cable(s)  62  and  64  based on the power ratio between the calibration signal(s) CS 1  and CS 2 and the respective return signal. Additionally, other types of characteristics can be monitored instead of or in addition to power, such as delay time, to determine the signal loss exhibited by the transmission line cable(s)  62  and  64 . The transmission line measurement circuit  70  can then store the determined signal loss in the memory  76 . For example, the memory  76  can store signal loss information for both of the transmission line cables  56  and  58  individually or in combination, and can store the signal loss information for each calibration operation or for the most recent calibration operation. As an example, the memory  76  can be configured as a non-volatile memory, such that the memory  76  can retain the calculated signal loss information during power loss of the antenna control circuit  50 . As a result, the calculated signal loss can be retrieved from the memory  76  after power is returned to the antenna control circuit  50  to facilitate operation of the antenna control circuit  50  without the need for a calibration operation. 
       FIGS.  3  and  4    illustrate example diagrams  100  and  150 , respectively, of calibration of a communication system. In the example of  FIG.  3   , the communication system includes a calibration circuit  102  and an antenna control circuit  104  that are communicatively coupled by a first transmission line cable  106  and a second transmission line cable  108 . In the example of  FIG.  4   , the communication system includes a calibration circuit  152  and an antenna control circuit  154  that are communicatively coupled by a first transmission line cable  156  and a second transmission line cable  158 . The calibration circuits in the examples of  FIGS.  3  and  4    can each correspond to the calibration circuit  20  in the example of  FIG.  1   , such as included in the antenna system  14 . As an example, the calibration circuits  102  and  152  can correspond to the calibration circuit  20 , the antenna control circuits  104  and  154  can correspond to the antenna control circuits  13  and/or  50 , and the transmission line cables  106  and  108  and the transmission line cables  156  and  158  can correspond to the transmission line cable(s)  16  and/or the transmission line cables  56  and  58 . Therefore, reference is to be made to the examples of  FIGS.  1  and  2    in the following description of the examples of  FIGS.  3  and  4   . 
     In the diagram  100 , the antenna control circuit  104  includes a transmission line measurement circuit  110 . During the calibration operation, the transmission line measurement circuit  110  can be configured (e.g., via the calibration signal generator  72 ) to generate a first calibration signal CS 1  that is transmitted by the transmission line measurement circuit  110  along the first transmission line cable  106 . The calibration circuit  102  can be configured to retransmit (e.g., reflect) the calibration signal CS 1  back to the antenna control circuit  104  as a respective return signal RTN 1  via the first transmission line cable  106 . Therefore, in the diagram  100 , the first transmission line  106  is configured to propagate both the calibration signal CS 1  and the reflected return signal RTN 1 . In response to receiving the return signal RTN 1 , the transmission line measurement circuit  110  can be configured (e.g., via the signal monitor  74 ) to measure the at least one characteristic of the reflected return signal RTN 1  to determine the signal loss exhibited by the first transmission line cable  106 . For example, the characteristic of the reflected return signal RTN 1  can be power, such that the transmission line measurement circuit  110  can calculate a power ratio between the calibration signal CS 1  and the respective reflected return signal RTN 1  to determine the signal loss exhibited by the first transmission line cable  106 . 
     Similarly, the transmission line measurement circuit  110  can repeat the previously described calibration procedure with respect to the second transmission line cable  108 . For example, the transmission line measurement circuit  110  can also be configured to generate a second calibration signal CS 2  that is transmitted by the transmission line measurement circuit  110  along the second transmission line cable  108 . The calibration circuit  102  can be configured to retransmit (e.g., reflect) the calibration signal CS 2  back to the antenna control circuit  104  as a respective return signal RTN 2  via the second transmission line cable  108 . In response to receiving the reflected return signal RTN 2 , the transmission line measurement circuit  110  can be configured (e.g., via the signal monitor  74 ) to measure the at least one characteristic of the reflected return signal RTN 2  to determine the signal loss exhibited by the second transmission line cable  108 , similar to as described previously with respect to the first transmission line cable  106 . 
     In the diagram  150 , the antenna control circuit  154  includes a transmission line measurement circuit  160 . During the calibration operation, the transmission line measurement circuit  160  can be configured (e.g., via the calibration signal generator  72 ) to generate a first calibration signal CS 1  that is transmitted by the transmission line measurement circuit  160  along the first transmission line cable  156 . The calibration circuit  152  can be configured to retransmit the calibration signal CS 1  back to the antenna control circuit  154  as a respective return signal RTN 1  via the second transmission line cable  158 . Therefore, in the diagram  150 , the first transmission line  156  is configured to propagate the calibration signal CS 1  and the second transmission line cable  158  is configured to propagate the return signal RTN 1 . In response to receiving the return signal RTN 1 , the transmission line measurement circuit  160  can be configured (e.g., via the signal monitor  74 ) to measure the at least one characteristic of the return signal RTN 1  to determine the signal loss exhibited by the first and second transmission line cables  156  and  158 . For example, the characteristic of the return signal RTN 1  can be power, such that the transmission line measurement circuit  160  can calculate a power ratio between the calibration signal CS 1  and the respective return signal RTN 1  to determine the signal loss exhibited by the first and second transmission line cables  156  and  158 . As an example, the transmission line measurement circuit  160  can either conclude the calibration operation, or can repeat the previously described calibration procedure with respect to switching the first and second transmission line cables  156  and  158  with respect to transmission of the calibration signal CS and receipt of the return signal RTN. 
       FIG.  5    illustrates an example of an antenna system  200 . The antenna system  200  can correspond to the antenna system  14  of the example of  FIG.  1   . Therefore, reference is to be made to the example of  FIG.  1    in the following description of the example of  FIG.  5   . 
     The antenna system  200  includes a first antenna array  202  and a second antenna array  204  that can each be associated with the respective signal diversity types. The antenna arrays  202  and  204  can be arranged as any of a variety of antenna arrays to provide a respective one or more wireless signals to be transmitted from and/or received at the antenna system  200 , demonstrated as respective signals RF 1  and RF 2 . For example, the antenna arrays  202  and  204  can include an arrangement of antenna elements (e.g., strip-line conductors) to provide the signal diversity between the two respective signal paths, such as based on polarization diversity. As an example, the antenna arrays  202  and  204  can be configured as separate respective arrays of orthogonally polarized antenna elements to provide orthogonal polarizations of signals propagating in the respective signal paths. The antenna arrays  202  and  204  can thus each transmit and receive signals in a TDD manner based on a defined standard on which the user communication system operates. 
     The antenna system  200  also includes a calibration circuit  205 , such as corresponding to the calibration circuit  20  in the example of  FIG.  1   . The calibration circuit  205  includes an extraction circuit  206  that can be configured as a DC decoupler (e.g., a bias--tee) that is coupled to the transmission line cables  56  and  58  to extract a DC voltage, demonstrated as a voltage V DC , that is provided, such as from the power block  64 , to power the electronics of the antenna system  200 . For example, the DC voltage V DC  can be a DC bias voltage that is provided on the transmission line cables  56  and  58 , such that the extraction circuit  206  extracts the voltage V DC  to provide power to the electronic components of the antenna system  200 . Therefore, the antenna system  200  does not require a local power source, such that the antenna system  200  can be installed in a more flexible manner. 
     The calibration circuit  205  includes a first signal port  208  and a second signal port  210  that are coupled to the antenna control circuit  50 . The first signal port  208  is configured to propagate the transmit and receive signals TS 1  via the transmission line cable  56  and the second signal port  210  is configured to propagate the transmit and receive signals TS 2  via the transmission line cable  58 . The first signal port  208  is coupled to the first transmission line cable  56  via a first switch SW 3  associated with the calibration circuit  205  and the second signal port  210  is coupled to the second transmission line cable  58  via a second switch SW 4  associated with the calibration circuit  205 . In the example of  FIG.  5   , the switches SW 3  and SW 4  are demonstrated as being set to a normal operating mode state, and are controlled via the calibration command CAL. For example, the calibration command CAL can correspond to the same calibration command CAL described in the example of  FIG.  2   , or can be a different calibration command (e.g., facilitated by a user or a change in operational DC voltage) that is to be provided during the calibration operation. 
     Therefore, in the normal operating mode, as in the state demonstrated in the example of  FIG.  5   , the switch SW 3  connects the first signal port  208  to the first transmission line cable  56  and the switch SW 4  connects the second signal port  210  to the second transmission line cable  58  to facilitate propagation of the transmit and receive signals between the antenna control circuit  50  and the antenna system  200  via the respective transmission line cables  56  and  58 . However, in the calibration mode, such as initiated by the calibration command CAL, the switches SW 3  and SW 4  can be switched to provide a short circuit between the transmission line cables  56  and  58 . As a result, the calibration signal CS 1 , such as provided in the example of  FIG.  4   , can be provided from the first transmission line cable  56  and can be retransmitted back to the antenna control circuit  50  as the return signal RTN 1  along the second transmission line cable  58 . Therefore, with minimal input, the antenna system  200  can be implemented in the calibration operation to determine the signal loss of the transmission line cables  56  and  58 . 
       FIG.  6    illustrates an example of an antenna system  230 . The antenna system  230  can correspond to the antenna system  14  of the example of  FIG.  1   . Therefore, reference is to be made to the example of  FIG.  1    in the following description of the example of  FIG.  6   . 
     The antenna system  230  includes a first antenna array  232  and a second antenna array  234  that can each be associated with the respective signal diversity types. The antenna arrays  232  and  234  can be arranged as any of a variety of antenna arrays to provide a respective one or more wireless signals to be transmitted from and/or received at the antenna system  230 , demonstrated as respective signals RF 1  and RF 2 . For example, the antenna arrays  232  and  234  can include an arrangement of antenna elements (e.g., strip-line conductors) to provide the signal diversity between the two respective signal paths, such as based on polarization diversity. As an example, the antenna arrays  232  and  234  can be configured as separate respective arrays of orthogonally polarized antenna elements to provide orthogonal polarizations of signals propagating in the respective signal paths. The antenna arrays  232  and  234  can thus each transmit and receive signals in a TDD manner based on a defined standard on which the user communication system operates. 
     The antenna system  230  also includes a calibration circuit  235 , such as corresponding to the calibration circuit  20  in the example of  FIG  1   . The calibration circuit  235  includes an extraction circuit  236  that can be configured as a DC decoupler (e.g., a bias-tee) that is coupled to the transmission line cables  56  and  58  to extract a DC voltage, demonstrated as a voltage V DC , that is provided, such as from the power block  64 , to power the electronics of the antenna system  230 . For example, the DC voltage V DC  can be a DC bias voltage that is provided on the transmission line cables  56  and  58 , such that the extraction circuit  236  extracts the voltage V DC  to provide power to the electronic components of the antenna system  230 . Therefore, the antenna system  230  does not require a local power source, such that the antenna system  230  can be installed in a more flexible manner. 
     The antenna system  230  includes a first signal port  238  and a second signal port  240  that are coupled to the antenna control circuit  50 . The first signal port  238  is configured to propagate the transmit and receive signals TS via the transmission line cable  56  and the second signal port  240  is configured to propagate the transmit and receive signals TS 2  via the transmission line cable  58 . The first signal port  238  is coupled to the first transmission line cable  56  via a first switch SW 3  associated with the calibration circuit  235  and the second signal port  240  is coupled to the second transmission line cable  58  via a second switch SW 4  associated with the calibration circuit  235 . In the example of  FIG.  5   , the switches SW 3  and SW 4  are demonstrated as being set to a normal operating mode state, and are controlled via the calibration command CAL. For example, the calibration command CAL can correspond to the same calibration command CAL described in the example of  FIG.  2   , or can be a different calibration command (e.g., facilitated by a user) that is to be provided during the calibration operation. 
     Therefore, in the normal operating mode, as in the state demonstrated in the example of  FIG.  6   , the switch SW 3  connects the first signal port  238  to the first transmission line cable  56  and the switch SW 4  connects the second signal port  240  to the second transmission line cable  58  to facilitate propagation of the transmit and receive signals between the antenna control circuit  50  and the antenna system  230  via the respective transmission line cables  56  and  58 . However, in the calibration mode, such as initiated by the calibration command CAL, the switches SW 3  and SW 4  can be switched to couple each of the transmission line cables  56  and  58  to ground. As a result, the calibration signal CS 1 , such as provided in the example of  FIG.  3   , can be provided from the first transmission line cable  56  and can be reflected back to the antenna control circuit  50  as the return signal RTN 1  along the first transmission line cable  56 . Similarly, the calibration signal CS 2 , such as provided in the example of  FIG.  3   , can be provided from the second transmission line cable  58  and can be reflected back to the antenna control circuit  50  as the return signal RTN 2  along the second transmission line cable  58 . Therefore, with minimal input, the calibration circuit  230  can be implemented in the calibration operation to determine the signal loss of the transmission line cables  56  and  58 . 
       FIG.  7    illustrates an example of a transmission line measurement circuit  250 . The transmission line measurement circuit  250  can correspond to the transmission line measurement circuit  70  in the example of  FIG.  2   . Therefore, reference is to be made to the examples of  FIGS.  2 - 6    in the following description of the example of  FIG.  7   . 
     As described previously, the transmission line measurement circuit  250  is configured to determine a signal loss between the antenna system (e.g., the antenna system  14 , or one of the antenna systems  200  and  230 ) and the antenna control circuit  50  through the transmission line cables  56  and  58 . In the example of  FIG.  7   , the transmission line measurement circuit  250  includes a calibration signal generator  252  and a signal monitor  254 . The calibration signal generator  252  includes an RF signal source  256  that is configured to generate a calibration signal that can correspond to the first calibration signal CS 1 . As an example, the first calibration signal CS 1  can correspond to a dummy RF signal (e.g., a sinusoidal signal) having a predefined frequency. In the example of  FIG.  7   , the calibration signal generator  252  includes a resistive network  258  that includes a first resistor R 1  and a second resistor R 2  that are each connected to the RF signal source  256  and to a third resistor R 3  opposite the RF signal source  256  and interconnecting the first and second resistors R 1 and R 2 . The resistive network  258  can thus provide a divided version of the first calibration signal CS 1  that can be provided to the first transmission line cable  56  (e.g., via the switch SW 1 ) in the calibration mode. The transmission line measurement circuit  250  can thus transmit the calibration signal CS 1  to the antenna system via the transmission line cable  56 . 
     As described previously, the antenna system can be configured to retransmit the calibration signal CS 1  back to the antenna control circuit  50  from the antenna system as respective return signal RTN 1  on the transmission line cable  58 , such as described in the example of  FIG.  4    during the calibration procedure. In the example of  FIG.  7   , the return signal RTN 1  is provided to the signal monitor  254  via a diode D 1 . The signal monitor  254  is also configured to receive a divided version of the first calibration signal CS 1 , demonstrated as a signal CS 1D , via a diode D 2 . Therefore, as an example, the signal monitor  254  can be configured to measure a power of each of the return signal RTN 1  and the signal CS 1D . As a result, the signal monitor  254  can calculate a power ratio between the return signal RTN 1  and the signal CS 1D . Accordingly, the signal monitor  254  can determine the signal loss exhibited by the transmission line cables  56  and  58  based on the power ratio between the return signal RTN 1  and the signal CS 1D . The power monitor  254  can thus provide the calculated signal loss, demonstrated as a signal PWR_LS, to the memory  76 . 
     While the transmission line measurement circuit  250  is configured to provide the calibration operation demonstrated in the example of  FIG.  4   , it is to be understood that the transmission line measurement circuit  250  is not limited to the example of  FIG.  7   . For example, the transmission line measurement circuit  250  can be arranged in a manner to facilitate the calibration signal CS 1  and the return signal RTN 1  or the calibration signal CS 2  and the return signal RTN 2  to be propagated along a given one of the transmission line cables  56  and  58 , such as described in the example of  FIG.  3   . 
     Referring back to the example of  FIG.  2   , the antenna control circuit  50  also includes a controller  78 . In response to the determining the signal loss, the transmission line measurement circuit  70  can provide the determined signal loss, demonstrated in the example of  FIG.  2    as “SM”, to the controller  78  (e.g., from the memory). In response to the determined signal loss SM, the controller  78  can be configured to adjust an amplitude of at least one of the transmit signals transmitted from the antenna control circuit  50  and the receive signals received at the antenna control circuit  50  based on the determined signal loss. As an example, the controller  78  can include a processor that is configured to determine the appropriate adjustments to the amplitude of each of the respective transmit and receive signals based on the determined signal loss SM. While the controller  78  is described as including a processor, the term “processor” can be used to describe other types of processing devices, such as a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), or other type of processing device. In the example of  FIG.  2   , the controller  78  is configured to provide control signals, demonstrated as “AT 1 ” and “AT 2 ”, respectively, to the amplitude adjustment circuits  60  and  62  based on the determined signal loss SM, as well as based on whether the signal paths  54  and/or  56  are in the transmit mode or the receive mode. 
     For example, the communication system  10  can be configured to operate based on a predetermined communication standard that can dictate a predetermined maximum effective isotropic radiated power (EIRP), such as +23 dBm for the transmit signals. Therefore, the controller  78  provides the control signals AT 1  and AT 2  to the respective amplitude adjustment circuits  60  and  62  in the transmit mode to attenuate the transmit signals down to less than the predetermined maximum EIRP. For example, the antenna arrays  202  and  204  or the antenna arrays  232  and  234  can be designed with sufficiently high gain to provide the transmit signals at a power level that is greater than the predetermined maximum EIRP to overcome power losses of the transmission line cables  56  and  58  regardless of the length of the transmission line cables  56  and  58 , such that the transmit signals can be attenuated down to approximately the predetermined maximum EIRP. Additionally or alternatively, the signal paths  52  and  54  can include sufficient power amplification in the transmit mode, as described in greater detail herein, to overcome power losses of the transmission line cables  56  and  58  regardless of the length of the transmission line cables  56  and  58 , such that the transmit signals can be attenuated down to approximately the predetermined maximum EIRP. Similarly, the controller  78  provides the control signals AT 1  and AT 2  to the respective amplitude adjustment circuits  60  and  62  in the receive mode to attenuate the receive signals down to less than an acceptable operational level (e.g., a maximum saturation power associated with the antenna control circuit  50  and/or the user communication system  12 ). Therefore, the antenna system  14  can be installed in a manner that is substantially agnostic of the length and/or loss characteristics of the transmission line cables  56  and  58  based on the calibration operation to determine the signal loss of the transmission line cables  56  and  58 . 
     In addition, in the example of  FIG.  2   , the controller  78  can also be configured to provide continuous voltage or tone signal monitoring of the transmission line cables  56  and  58  to determine a fault condition and/or a calibration failure. In response to detecting a fault condition and/or a calibration failure, the controller  78  can each assert respective signals FLT 1  and FLT 2  that are provided to respective switches SW 5  and SW 6 . The switches SW 5  and SW 6  can therefore terminate the signal paths  52  and  54  to grounded resistors to provide isolation and/or termination of the signal paths  52  and  54  to separate the antenna system  14  from the user communication equipment  12  in the event of the fault condition and/or the calibration failure. Such a termination of the signal paths  52  and  54  to a load via the switches SW 5  and SW 6  can also mitigate external unwanted signals from corrupting the calibration. As another example, the controller  78  can instead control an isolation or termination switch in the amplitude adjustment circuits  60  and  62 , respectively, for the isolation and/or termination of the signal paths  52  and  54  in the event of a fault condition and/or calibration failure. 
     In the example of  FIG.  2   , as one example, the controller  78  can provide a calibration voltage V CAL  at the connection “A” to the injection circuit  68 . The calibration voltage V CAL  is thus transmitted to the antenna system  14  via the transmission line  58 , such that the voltage V CAL  can be provided back to the antenna circuit  50  via the transmission line  56  (e.g., via the calibration circuit  205  in the example of  FIG.  5   ). If the controller  78  does not detect the voltage V CAL  via the transmission line  56  (e.g., having been provided from the calibration circuit  205 ), the controller  78  can indicate a fault and/or a calibration failure. Therefore, the controller  78  can monitor the continuity of the communication system  10 , and in the event of a short-circuit or a failure/disconnection of the transmission lines  56  and  58 , the controller  78  can remove the voltage thus automatically terminating the antenna system  200  or  230  and can assert the fault signals FLT 1  and FLT 2  to terminate the user communication equipment  12 . 
     Referring to the example of FIGS,  5  and  6 , the antenna systems  200  and  230  each include termination switches SW 7  and SW 8  to terminate the antenna arrays  202  and  204  or the antenna arrays  232  and  234  in response to the fault signals FLT 1  and FLT 2 . As an example, the controller  78  can initiate a calibration sequence by applying a voltage or tone signal onto the transmission lines  56  and  58 . The extraction circuits  206  and  236  can also include a voltage or tone detection circuit that switches the antenna systems  200  and  230  to a calibration state. During the calibration state or the when the voltage V DC  is faulted, the antenna systems  200  and  230  can automatically switch the antenna arrays  202  and  204  or the antenna arrays  232  and  234  to a load resistor (e.g., via the switches SW 7  and SW 8 ) to prevent transmission during fault conditions and to reduce external interference and unwanted signals from corrupting the calibration. 
     Referring back to the example of  FIG.  2   , as described previously, the communication system  10  can operate based on a TDD communication standard, such that the transmit signals and the receive signals can be interleaved with each other on a given signal path between the user communication system  12  and the antenna arrays  202  and  204  or the antenna arrays  232  and  234 . In addition, as described previously, the signal paths  52  and  54  of the antenna control circuit  50  can operate in either a transmit mode or a receive mode corresponding to transmission of the transmit signals or receipt of the receive signals in the TDD manner along the respective signal paths  52  and  54 . In the example of  FIG.  2   , the antenna control circuit  50  also includes a first transmit detection circuit  80  associated with the first signal path  52  and a second transmit detection circuit  82  associated with the second signal path  54 . The transmit detection circuits  80  and  82  can be configured to measure power on the respective signal paths  52  and  54  to determine if the user communication system  12  is transmitting a transmit signal. 
     For example, the transmit detection circuits  80  and  82  can each include a bi-directional coupler with a terminated load to determine if the power on the respective one of the signal paths  52  and  54  is greater than a predetermined threshold to determine if the user communication system  12  is transmitting a transmit signal. In the example of  FIG.  2   , the transmit detection circuits  80  and  82  are configured to generate mode signals TX 1  and TX 2  that are provided to the controller  78 , such as to indicate that the respective one of the signal paths  52  and  54  is in the transmit mode. Therefore, in response to the transmit detection circuits  80  and  82  determining if the user communication system  12  is transmitting a transmit signal, the controller  78  can switch the respective signal paths  52  and  54  from the receive mode as a default mode to a transmit mode to facilitate transmission of the transmit signal from the antenna control circuit  50  via the antenna arrays  202  and  204  or the antenna arrays  232  and  234 . Similarly, in response to the transmit detection circuits  80  and  82  detecting a decrease in the power of the signal path (e.g., less than the predetermined threshold), the controller  78  can switch the respective signal paths  52  and  54  back to the receive mode from the transmit mode (e.g., upon expiration of a timer). 
     As described previously, the controller  78  can be configured to adjust the respective control signal(s) AT 1  and AT 2  based on the indication of the transmit mode or the receive mode of the respective one of the signal paths  52  and  54 , such as based on the respective mode signals TX 1  and TX 2 . Therefore, the amplitude of the transmit and receive signals can be adjusted (e.g., attenuated) based on whether the respective signal path  52  or  54  is in the transmit mode or the receive mode. As another example, as described previously, the amplitude adjustment circuits  60  and  62  can switch between a transmit mode signal path and a receive mode signal path for each of the amplitude adjustment circuits  60  and  62  via switches. Therefore, the controller  78  can also include a switch controller  84  that is configured to control the switches of the amplitude adjustment circuits  60  and  62 . 
     As an example, the switch controller  84  can be configured to generate mode signals MD 1  and MD 2 , respectively, to control the mode of the respective one of the signal paths  52  and  54 . For example, the amplitude adjustment circuit  60  can be controlled by the first switching signal MD 1  and the amplitude adjustment circuit  62  can be controlled by the second switching signal MD 2 . In response to one of the transmit detection circuits  80  and  82  determining that the user communication system  12  is transmitting a transmit signal along the respective one of the signal paths  52  and  54 , the respective one of the transmit detection circuits  80  and  82  commands the controller  78  (e.g., via the mode signals TX 1  and TX 2 ) to provide the respective one of the switching signals MD 1  and MD 2  to the respective one of the amplitude adjustment circuits  60  and  62 . In response to the respective one of the switching signals MD 1  and MD 2 , the respective amplitude adjustment circuits  60  and  62  can activate at least one switch to switch the respective amplitude adjustment circuits  60  or  62  from the default receive mode to the transmit mode to facilitate transmission of the transmit signal along the respective signal path  52  and  54  and from the respective antenna array  58  and  60 . 
       FIG.  8    illustrates an example of a controller  300 . The controller  300  can correspond to the controller  78  in the example of  FIG.  2   . Therefore, reference is to be made to the example of  FIG.  2    in the following description of the example of  FIG.  8   . 
     The controller  300  includes a processor  302 . For example, the processor  302  can communicate with or include the amplitude adjustment circuits  60  and  62 . In the example of  FIG.  8   , the processor  302  receives the signal SM corresponding to the signal loss of the transmission line cables  56  and  58 . Therefore, the processor  302  can be configured to calculate the appropriate amount of amplification (e.g., attenuation) to provide to the amplitude adjustment circuits  60  and  62 , such as to provide the appropriate attenuation to the signal paths  52  and/or  54  based on the respective mode (e.g., transmit mode or receive mode). In the example of  FIG.  7   , the processor  302  is demonstrated as generating the control signals AT 1  and AT 2  that are provided to the amplitude adjustment circuits  60  and  62 , such as to provide the appropriate attenuation to the signal paths  52  and/or  54  based on the respective mode. 
     As described previously, the controller  78  in the example of  FIG.  2    can include the switching controller  94  to control the switches of the amplitude adjustment circuits  60  and  62 . In the example of  FIG.  8   , the controller  300  can include a switching controller  304  that can provide a switching signal MD for one of the amplitude adjustment circuits  60  and  62 . Therefore, it is to be understood that the controller  300  can include a switching controller  304  for each of the signal paths  52  and  54 . The switching controller  304  includes a first comparator  306  and a second comparator  308 . The first comparator  306  is configured to compare a voltage V RX  corresponding to an approximate power of the receive signals with a threshold voltage V RX_TH . Similarly, the second comparator  308  is configured to compare a voltage V TX  corresponding to an approximate power of the transmit signals with a threshold voltage V TX_TH . As an example, the voltages V RX  and V TX  can correspond to the same voltage (e.g., corresponding to the signal power on a given one of the signal paths  52  and  54 , as measured by the transmit detection system(s)  90  and  92 . Therefore, the comparators  306  and  308  can be configured to provide an asserted output corresponding to the mode of the respective signal path  52  or  54 . 
     The switching controller  304  includes a first sequence of D latches (e.g., flip-flops), demonstrated as  310 ,  312 , and  314 . The first D latch  310  receives the output of the first comparator  306  as an input, with the D latches  310 ,  312 , and  314  being configured in a cascaded arrangement from output to input. Each of the D latches  310 ,  312 , and  314  receives a clock signal CLK from an oscillator  316 . The output of the second D latch  312  and the third D latch  314  are provided as inputs to an AND-gate  318 , with the input received from the third D latch  314  being inverted. In a similar arrangement, the switching controller also includes a second sequence of D latches, demonstrated as  320 ,  322 , and  324 . The first D latch  320  receives the output of the second comparator  308  as an input, with the D latches  320 ,  322 , and  324  being configured in a cascaded arrangement from output to input. Each of the D latches  320 ,  322 , and  324  likewise receives the clock signal CLK. The output of the second D latch  322  and the third D latch  324  are provided as inputs to an AND-gate  326 , with the input received from the third D latch  324  being inverted. 
     The output of the AND-gate  318  is provided as a set input to an SR latch  328 , and the output of the AND-gate  326  is provided as a reset input to the SR latch  328 . The SR latch  328  likewise the clock signal CLK, and is configured to generate the respective switching signal MD (e.g., one of the switching signals MD 1  and MD 2 ). Therefore, the SR latch  328  is configured to rapidly change the state of the switching signal MD in response to a change in amplitude of the voltages V TX  and/or V RX . For example, in response to a change of the amplitude of the voltages V TX  and/or V RX , the logic sequence of the D latches  310 ,  312 ,  314 ,  320 ,  322 , and  324 , the AND-gates  318  and  326 , and the SR latch  328  can be configured to change the state of the switching signal MD in a time of approximately 10 microseconds or less, such as to satisfy the TDD communication standard. 
     The processor  302  can be configured to receive a plurality of inputs associated with the switching logic of the switching controller  304 . In the example of  FIG.  8   , the processor  302  receives as inputs the output of the D latches  314  and  324 , as well as the outputs of the AND-gates  318  and  326 . For example, the processor  302  can be configured as a state machine to monitor the state of the signal path (e.g., the signal path  52  or  54 ), such that the inputs to the inputs to the processor  302  are configured to set flags and/or registers for operation of the antenna control circuit  50 . As another example, the oscillator  316  can be included in the processor  302 , such that the processor  302  generates the clock signal CLK. Additionally, the processor  302  is demonstrated as generating the predetermined threshold voltages V TX_TH  and V RX_TH , which can be programmable via input to the processor  302 , or can have fixed voltage amplitudes. 
     In the example of  FIG.  8   , the processor  302  includes timers  330  (e.g., one for each of the signal paths  52  and  54 ). As an example, the timers  330  can correspond to watchdog timers for controlling timing associated with the mode selection of the respective signal paths  52  and  54 . For example, in response to the inputs provided to the processor  302  indicating that the mode is set for transmit mode for a given one of the signal path(s)  52  and  54 , but the transmit power is less than the predetermine threshold (e.g., the voltage V TX  is less than the predetermined threshold V TX_TH ), the respective timer  330  can begin counting a predetermined timing threshold. As an example, in response to the respective tinier  330  counting for a predetermined time duration (e.g., approximately one millisecond), the processor  302  can switch back to a default receive mode for the given signal path  52  or  54  such as to change the amplitude of the respective one of the control signals AT 1  and AT 2 . Additionally, the processor  302  can assert an output to the SR latch  328  (e.g., to a “clear” input of the SR latch  328 ). Therefore, the SR latch  328  can reset to change the state of the switching signal MD to indicate switching the mode from the transmit mode back to the receive mode. As a result, the signal path(s)  52  and/or  54  can be returned to the default receive mode in response to the timed indication of no more transmit signals being transmitted from the user communication system  12 . 
     In order to satisfy a given TDD communication standard, the control signals AT 1  and AT 2  and the amplitude adjustment circuits  60  and  62  may be required to switch between the transmit mode and the receive mode as quickly as possible.  FIG.  9    illustrates an example diagram  350  of a TDD communication stream. The TDD communication stream includes a first set of receive signal sub-frames, demonstrated at  352 , a first set of transmit signal sub-frames, demonstrated at  354 , and a second set of receive mode sub-frames  356 . As an example, the TDD communication stream can continue thereafter with alternating sets of transmit signal sub-frames and receive signa sub-frames in a TDD manner. The transmit and receive signal sub-frames are demonstrated in the example of  FIG.  9    as being demonstrated as a function of time. While each of the transmit and receive signal sub-frames are demonstrated as being approximately equal in time, it is to be understood that the transmit and receive signal sub-frames are not necessarily equal in length of time, and that the elements of the time domain demonstrated in the example of  FIG.  9    are not necessarily illustrated to scale. 
     In the example of  FIG.  9   , between each of the sets of receive signal sub-frames (e.g., the receive signal sub-frames  352 ) and transmit signal sub-frames (e.g., the transmit signal sub-frames  354 ) is a time T INT . The time T INT  can, for example, correspond to a substantial maximum intermediate time between propagation of the receive signal sub-frames and the transmit signal sub-frames on a given signal path, such as between the user communication system  12 , along a transmission line cable  56  or  58 , along a respective signal path  52  or  54  in the antenna control circuit  50 , and a respective one of the antenna arrays  202  or  204 , such as defined by the predetermined TDD communication standard. 
     In the example of  FIG.  9   , the time T INT  between each of the transmit and receive signal sub-frames includes a first portion of time  358  and a second portion of time  360 . The first portion of time  358  can correspond to a switching time (e.g., approximately 10 microseconds or less), such as to generate the appropriate switching signal(s) MD 1  and MD 2  and/or to activate the respective switches of the amplitude adjustment circuits  60  and  62 . The second portion of time  360  can correspond to switch settling time (e.g., likewise approximately 10 microseconds or less), such as a time for the respective switches to settle to a saturation region and/or to dissipate parasitic effects (e.g., capacitance and/or inductance) of the circuit components of the switching controller  304  and/or the respective amplitude adjustment circuits  60  and  62 . Therefore, the hardware-based logic circuit of the switching controller  304  can implement rapid state-changes of the switching signal(s) MD 1  and MD 1  to satisfy the rapid switching requirements dictated by the TDD communication standard. 
       FIGS.  10 - 15    demonstrate examples of amplitude adjustment circuits. The example of  FIG.  10    demonstrates an amplitude adjustment circuit  370 , the example of  FIG.  11    demonstrates an amplitude adjustment circuit  400 , the example of  FIG.  12    demonstrates an amplitude adjustment circuit  450 , the example of  FIG.  13    demonstrates an amplitude adjustment circuit  500 , the example of  FIG.  14    demonstrates an amplitude adjustment circuit  550 , and the example of  FIG.  15    demonstrates an amplitude adjustment circuit  600 . Any of the amplitude adjustment circuits  370 ,  400 ,  450 ,  500 ,  550 , and  600  can correspond to the amplitude adjustment circuits  60  and  62  in the example of  FIG.  2   . Therefore, reference is to be made to the example of  FIG.  2    in the following description of the examples of  FIGS.  10 - 15   . 
     Additionally, the amplitude adjustment circuits  370 ,  400 ,  450 ,  500 ,  550 , and  600  are not limited to the examples demonstrated in the examples of  FIGS.  10 - 15   . For example, the amplitude adjustment circuits  370 ,  400 ,  450 ,  500 ,  550 , and  600  can include filters, such as low-noise filters, bandpass filters, and the like that can be arranged in the respective transmit path, receive path, or both. As another example, the amplitude adjustment circuits  370 ,  400 ,  450 ,  500 ,  550 , and  600  described in the examples of  FIGS.  10 - 15    are not limited to providing amplification in each of the transmit path and receive path, but can instead include a signal bypass path (e.g., zero gain) in either the transmit path or the receive path. As another example, each of the amplitude adjustment circuits  370 ,  400 ,  450 ,  500 ,  550 , and  600  can include isolation or termination switches (not shown), such as controlled via the transmit detection circuits  80  and  82 , to provide isolation and/or termination of the respective signal paths  52  and  54  to separate the antenna system  14  from the user communication equipment  12  in the event of a fault condition and/or a calibration failure. Furthermore, the switches described in the amplitude adjustment circuits  400 ,  450 ,  500 ,  550 , and  600  can be implemented as transistor devices, such as to provide very rapid switching times between the transmit mode and the receive mode. 
     In the example of  FIG.  10   , the amplitude adjustment circuit  370  includes a VCE  372  in the signal path (e.g., the signal path  52  or  54 . The VCE  372  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  372  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). Therefore, the mode of the amplitude adjustment circuit  370  is controlled by the amount of adjustment (e.g., attenuation) provided by the control signal AT in each of the transmit mode and the receive mode. 
     In the example of  FIG.  11   , the amplitude adjustment circuit  400  includes a VCE  401  in the signal path (e.g., the signal path  52  or  54 ). The VCE  401  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  401  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). The amplitude adjustment circuit  400  also includes first switch SW 5 , a second switch SW 6 , and a third switch SW 7  that are each controlled by the switching signal MD. The switches SW 5 , SW 6 , and SW 7  are demonstrated in a default state corresponding to the default state of the receive mode. The first and second switches SW 5  and SW 6  are each demonstrated in the example of  FIG.  11    as single-pole double-throw switches that select between a first signal path, demonstrated at  402 , and a second signal path, demonstrated at  404 . In the example of  FIG.  11   , the first signal path  402  can correspond to the receive mode and the second signal path  404  can correspond to the transmit mode. The second signal path  404  includes a power amplifier  406  that is configured to amplify the transmit signal in the transmit mode. Additionally, the amplitude adjustment circuit  400  includes a low-noise amplifier (LNA)  408  that is arranged in parallel with the third switch SW 7 , arranged as a single-pole single-throw switch. Therefore, in the receive mode, the receive signal is amplified by the LNA  408 , and in the transmit mode, the transmit signal is provided in a bypass short-circuit through the closed switch SW 7 . 
     In the example of  FIG.  12   , the amplitude adjustment circuit  450  includes a VCE  451  in the signal path (e.g., the signal path  52  or  54 . The VCE  451  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  451  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). The amplitude adjustment circuit  450  also includes a first circulator  452 , a second circulator  454 , a first switch SW 5 , and a second switch SW 6  that are each controlled by the switching signal MD. The switches SW 5  and SW 6  are demonstrated in a default state corresponding to the default state of the receive mode. The first and second switches SW 5  and SW 6  are each demonstrated in the example of  FIG.  11    as single-pole double-throw switches. The first circulator  452  is demonstrated as a “clockwise” circulator, such that the transmit signal is provided to the first switch SW 5 . The first switch SW 5  selects between an attenuator  456  in the receive mode and a power amplifier  458  in the transmit mode, and thus is output from the amplitude adjustment circuit  450  via the second circulator  454  that is also arranged as a “clockwise” circulator. The second circulator  454  also provides the receive signal to the second switch SW 6 . The second switch SW 6  selects between an attenuator  460  in the transmit mode and an LNA  462  in the receive mode, and thus is output from the amplitude adjustment circuit  450  via the first circulator  452 . 
     In the example of  FIG.  13   , the amplitude adjustment circuit  500  includes a VCE  501  in the signal path (e.g., the signal path  52  or  54 ). The VCE  501  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  501  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). The amplitude adjustment circuit  500  also includes a switch SW 5  and a circulator  502 . The switch SW 5  is arranged as a single-pole double-throw switch controlled by the switching signal MD, and is demonstrated in a default state corresponding to the default state of the receive mode. The switch SW 5  selects between a first signal path, demonstrated at  504 , and a second signal path, demonstrated at  506 . In the example of  FIG.  13   , the first signal path  504  can correspond to the transmit mode and the second signal path  506  can correspond to the receive mode. The first signal path  504  includes a power amplifier  508  that is configured to amplify the transmit signal in the transmit mode, and thus is output from the amplitude adjustment circuit  500  via the circulator  502  that is also arranged as a “clockwise” circulator. The second signal path  506  includes an LNA  510 , such that the circulator  502  provides the receive signal on the second signal path  506  to be amplified by the LNA  510  and output from the amplitude adjustment circuit  500  via the switch SW 5  in the receive mode. 
     In the example of  FIG.  14   , the amplitude adjustment circuit  550  includes a VCE  551  in the signal path (e.g., the signal path  52  or  54 ). The VCE  551  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  551  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). The amplitude adjustment circuit  550  also includes a switch SW 5  and a circulator  552 . The switch SW 5  is arranged as a single-pole double-throw switch controlled by the switching signal MD, and is demonstrated in a default state corresponding to the default state of the receive mode. The switch SW 5  selects between a first signal path, demonstrated at  554 , and a second signal path, demonstrated at  556 . In the example of  FIG.  14   , the first signal path  554  can correspond to the transmit mode and the second signal path  556  can correspond to the receive mode. The first signal path  554  is demonstrated as a bypass short-circuit to output the transmit signal from the amplitude adjustment circuit  550  via the circulator  552  that is also arranged as a “clockwise” circulator. The second signal path  556  includes an LNA  558 , such that the circulator  552  provides the receive signal on the second signal path  556  to be amplified by the LNA  558  and output from the amplitude adjustment circuit  550  via the switch SW 5  in the receive mode. 
     In the example of  FIG.  15   , the amplitude adjustment circuit  600  includes a VCE  601  in the signal path (e.g., the signal path  52  or  54 ). The VCE  601  is demonstrated as being controlled by a control signal AT (e.g., one of the control signals AT 1  or AT 2 ). For example, the VCE  601  can be configured as a variable attenuator that is controlled by the controller  78  to provide attenuation of the transmit signals in the transmit mode and to provide attenuation of the receive signals in the receive mode (e.g., based on a respective one of the mode signals TX 1  or TX 2 ). The amplitude adjustment circuit  600  also includes a switch SW 5  controlled by the switching signal MD. The switch SW 5  is demonstrated as a single-pole single-throw switch in a default state corresponding to the default state of the receive mode. The amplitude adjustment circuit  600  includes an LNA  602  that is arranged in parallel with the switch SW 5 . Therefore, in the receive mode, the receive signal is amplified by the LNA  602 , and in the transmit mode, the transmit signal is provided in a bypass short-circuit through the closed switch SW 5 . 
     The examples of  FIGS.  10 ,  14 , and  15    do not include power amplifiers to provide amplification of the transmit signals in the transmit mode. As described previously, the signal paths  52  and  54  can include sufficient power amplification in the transmit mode, such as provided in the examples of  FIGS.  11 - 13    to overcome power losses of the transmission line cables  56  and  58  regardless of the length of the transmission line cables  56  and  58  (e.g., to attenuate the transmit signals down to approximately the predetermined maximum EIRP). As another example, the amplitude adjustment circuits  370 ,  550 , and  600  in the examples of  FIGS.  10 ,  14 , and  15   , respectively, can be implemented when the user communication system  12  includes sufficient power amplification of the transmit signals that power amplifiers are not necessary in the transmit signal paths. Additionally or alternatively, the antenna arrays  202  and  204  or the antenna arrays  232  and  234  can be designed with sufficiently high gain that power amplification of the transmit signals is not necessary in the transmit signal paths to provide feasibility of the amplitude adjustment circuits  550  and  600 . 
     As another example, the amplitude adjustment circuits  400 ,  450 , and  500  can be implemented for installation of an antenna system  14  in a manner that is completely agnostic of the user communication system  12 . For example, during the calibration procedure, in addition to measuring the signal loss of the transmission line cables  56  and  58 , the antenna control circuit  50  can measure an output power of the transmit signals provided from the user communication system  12  (e.g., via the transmit detection circuits  80  and  82 , such as relative to a plurality of thresholds). Therefore, in response to determining the output power of the user communication system  12 , the antenna control circuit  50  can properly attenuate the transmit signals in the transmit mode down to approximately the predetermined maximum EIRP. 
     As a result, the switching controller  304  can implement state changes of the switching signal MD in response to changes of amplitude of the voltages V TX  and/or V RX , such as in response to the transmit detection circuit(s)  80  and  82  detecting changes in power on the respective signal path(s)  52  and  54 . Accordingly, the switching signals MD 1  and MD 2  can provide sufficiently rapid switching to satisfy the maximum switching times (e.g., the first portion of time  558  in the example of  FIG.  9   ) to comply with the TDD communication standard. As a result, the antenna control circuit  50  can operate to facilitate the bidirectional TDD communications between transmit and receive signals, such as without requiring communication or signal transfer from the user communication system  12 . Therefore, the antenna system  14  can be installed in a simplistic manner that is largely independent of the operation of the user communication system  12 . Additionally, the antenna system  14  can be installed in a manner that is agnostic of the length of the transmission line cable(s)  56  and  58  interconnecting the antenna control circuit  50  and the user communication system  12 . Accordingly, the antenna control circuit  50  can be simplistically installed to efficiently facilitate wireless communication between the user communication system  12  and a network hub (e.g., a base station). 
     In view of the foregoing structural and functional features described above, a methodology in accordance with various aspects of the present invention will be better appreciated with reference to  FIG.  16   . While, for purposes of simplicity of explanation, the methodology of  FIG.  16    is shown and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some aspects could, in accordance with the present invention, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect of the present invention. 
       FIG.  16    illustrates an example of a method  650  for communicating at least one of a transmit signal and a receive signal via a TDD antenna communication system (e.g., the communication system  10 ) comprising an antenna system (e.g., the antenna system  14 ). At  652 , a calibration signal (e.g., the calibration signal(s) CS 1  and/or CS 2 ) is provided from an antenna control circuit (e.g., the antenna control circuit  13 ) to the antenna system on at least one transmission line cable (e.g., the transmission line cable(s)  16 ). At  654 , a returned signal (e.g., the return signal(s) RTN 1  and RTN 2 ) corresponding to the calibration signal retransmitted back from the antenna system is received at the antenna control circuit on the at least one transmission line cable. At  656 , signal loss between the antenna system and the antenna control circuit through at least one transmission line cable is determined (e.g., via the transmission line measurement circuit  22 ) based on the returned signal. At  658 , an amplitude of the receive signal received via the at last one transmission line cable is adjusted in a receive mode based on the determined signal loss. At  660 , signal power of the transmit signal obtained from the user communication system via the at least one transmission line cable is monitored (e.g., via the transmit detection circuit  28 ). At  662 , an amplitude adjustment circuit (e.g., the amplitude adjustment circuit  24 ) is switched from the receive mode to a transmit mode (e.g., via the controller  26 ) in response to the monitored signal power exceeding a predetermined threshold. At  664 , an amplitude of the transmit signal is adjusted in the transmit mode based on the determined signal loss. 
     What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. As used herein, the term “includes” means includes but not limited to, and the term “including” means including but not limited to. The term “based on” means based at least in part on.