Abstract:
The present invention provides a method and apparatus for carrying signals having different frequencies in a space-deployed antenna system. When the antenna system is in a first mode, DC power, command information and RF signals ( 1 ) are multiplexed via a multiplexer, ( 2 ) propagate along a RF transmission line and ( 3 ) are appropriately demultiplexed by a demultiplexer associated with each T/R module. Similarly, when the antenna system is in a second mode, telemetry data and RF signals ( 1 ) are multiplexed via a multiplexer, ( 2 ) propagate along the RF transmission line and ( 3 ) are appropriately demultiplexed by a demultiplexer at a driver stage. By using the RF transmission lines associated with each T/R module to deliver ( 1 ) DC power, ( 2 ) command data and ( 3 ) RF signals in the first mode and to deliver ( 1 ) telemetry data and ( 2 ) RF signals in the second mode, the DC power and command/telemetry wire harnesses (and their respective conductors) may be eliminated. Thus, the overall weight of the antenna system may be reduced. Furthermore, deployment risks may be reduced. Finally, the overall cost of the antenna system may be reduced.

Description:
FIELD OF THE INVENTION 
     The present invention relates to antenna systems and, more particularly, to antenna systems which are deployed in space. 
     BACKGROUND OF THE INVENTION 
     A communications satellite is an artificial satellite placed into orbit around earth to, among other things, facilitate communications on earth. Communications satellites normally include antenna systems, which typically receive information from and transmit information to various locations on earth. 
     Phased-array antenna systems, which are well-known, are one type of antenna system that has been used with communications satellites. A phased-array antenna system is comprised of a plurality of antenna elements which are suitably spaced relative to one another. The antenna system generates a radiation pattern having a shape and direction that is determined by the combination of the relative phases and amplitudes of the signals applied to the antenna elements. By varying the relative phases of the signals applied to the antenna elements, the antenna&#39;s direction of radiation may be steered. 
     Conventional phased-array antenna systems typically include a driver stage, a plurality of transmit/receive modules (“T/R modules”) and an RF feed network comprised of RF transmission lines. In addition, such antenna systems include a DC power wire harness having a plurality of DC power signal conductors and a digital command/telemetry signal wire harness having a plurality of command/telemetry signal conductors. 
     Thus, typically, in conventional phased-array antenna systems, each T/R module is electrically connected to the driver stage via ( 1 ) an RF transmission line, ( 2 ) a DC power signal conductor from the DC power wire harness and ( 3 ) a command/telemetry signal conductor from the digital command/telemetry signal wire harness. Both the DC power signal conductors and the command/telemetry signal conductors are typically several meters (or more) in length and require shielding, sheathing, connectors and connector back shells. Furthermore, both the DC power wire harness and the digital command/telemetry signal wire harness require mounting hardware. Thus, when a phased-array antenna system includes hundreds or more TIR modules, the complexity and weight of the system increases dramatically due to the presence of the DC power wire harness, digital command/telemetry signal wire harness and their respective conductors. 
     When communications satellites are deployed into space, costs associated with delivering spacecraft payloads into the earth&#39;s orbit are based on the payload&#39;s weight. Thus, there is a need to reduce the weight of antenna systems associated with communications satellites. In addition, because antenna deployment is one of the highest risk components of a space-based satellite mission, there is a need to reduce antenna deployment risks. Finally, there is a need to reduce antenna costs, including costs related to procurement, testing and installation. 
     SUMMARY OF THE INVENTION 
     The present invention is designed to overcome the aforementioned problems and meet the aforementioned, and other, needs. 
     It is an object of the present invention to reduce the weight of antenna systems associated with communications satellites. 
     It is another object of the invention to reduce antenna deployment risks. 
     It is yet another object of the invention to reduce antenna costs, including costs related to procurement, testing and installation. 
     In accordance with the objects of the invention, the present invention advantageously reduces the number of electrical connections made to each T/R module. More specifically, the present invention eliminates both the DC power wire harness and the digital command/telemetry wire harness (and their respective conductors), while still providing their associated signals from the driver stage to each T/R module. Even more specifically, when the antenna is in a first mode, DC power, command information and RF signals ( 1 ) are multiplexed via a multiplexer, ( 2 ) propagate along the RF transmission line and ( 3 ) are appropriately demultiplexed by a demultiplexer associated with each T/R module. Similarly, when the antenna is in a second mode, telemetry or operations-related data (including, e.g., status information) and RF signals ( 1 ) are multiplexed via a multiplexer, ( 2 ) propagate along the RF transmission line and ( 3 ) are appropriately demultiplexed by a demultiplexer at the driver stage. 
     By using the RF transmission lines associated with each T/R module to deliver ( 1 ) DC power, ( 2 ) command data and ( 3 ) RF signals in a first mode and to deliver ( 1 ) telemetry data and ( 2 ) RF signals in a second mode, the DC power and command/telemetry wire harnesses (and their respective conductors) may be eliminated. Thus, the overall weight of the antenna system may be reduced. Furthermore, deployment risks may be reduced since, in conventional systems, both the DC power wire harness and command/telemetry wire harness (and their respective conductors) may inhibit deployment mechanisms. Finally, the overall cost of the antenna system may be reduced since the components required to implement the multiplexer/demultiplexer circuits can be realized in inexpensive, silicon integrated circuits (or alternatively in discrete form) placed in each T/R module and in the driver stage. In contrast, there is relatively greater expense in procuring, testing and installing conventional wire harnesses and connecting them from the driver stage to each T/R module via DC power signal conductors and command/telemetry signal conductors. 
     Other objects, features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified block diagram of an embodiment of the present invention, wherein command data, DC power and RF signals are being provided from the driver stage to the T/R modules without a DC power wire harness nor a command/telemetry wire harness (or their respective conductors); 
     FIG. 2 is a circuit diagram of the multiplexer shown in FIG. 1 for an embodiment of the present invention; 
     FIG. 3 is a circuit diagram of the demultiplexer shown in FIG. 1 for an embodiment of the present invention; 
     FIG. 4 is a block diagram of an embodiment of the present invention generally showing two modes in which the antenna system may operate; 
     FIG. 5 is a frequency plot showing the relative frequencies of the DC power signal, command signal, telemetry signal and RF signal for an embodiment of the present invention in a half-duplex configuration; and, 
     FIG. 6 is a frequency plot showing the relative frequencies of the DC power signal, command signal, telemetry signal and RF signal for an embodiment of the present invention in a full-duplex configuration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiments in many different forms, there are shown in the drawings and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated. 
     FIG. 1 is a simplified block diagram of an embodiment of the phased-array antenna system  100  of the present invention, wherein control or command signals, DC power and RF signals, carrying data or other information, are to be provided from a driver stage  102  to each T/R module  104 . The antenna system  100  includes a driver stage  102 , T/R modules  104 , antenna elements  105  and an RF feed network  106 . The RF feed network  106  includes RF transmission lines  108 . Each of these lines  108  includes a single, preferably, center conductor that is used to carry all of the control/command, DC power and RF signals between the driver stage  102  and the T/R modules  104 . As will be understood by those skilled in the art, the antenna system  100  shown in FIG. 1 is an active array, in that it includes separate T/R modules  104  for each antenna element  105 . 
     In contrast to typical phased-array antenna systems, the antenna system  100  shown in FIG. 1 does not include a DC power wire harness or a digital command/telemetry signal wire harness (or their respective conductors). Instead, the phased-array antenna system  100  includes a multiplexer  110  (to be explained in further detail in connection with FIG. 2) preferably located proximate (or “within”) the driver stage  102  and a plurality of demultiplexers  112  (to be explained in further detail in connection with FIG. 3) preferably located proximate (or “within”) each T/R module  104 . 
     When the antenna  100  is in transmit mode, the multiplexer  110  combines command signal  114 , DC power signal  116  and RF signal  118  and transmits the combination of such signals across the RF feed network  106  via the RF transmission lines  108 . The combined signal is received at each T/R module  104  and is demultiplexed via the demultiplexer  112  associated with each T/R module  104  to obtain command signal  120 , DC power signal  122  and RF signal  124  at each T/R module  104 . Accordingly, the DC power wire harness and the digital command/telemetry signal wire harness (and their respective conductors), which are found in typical phased-array antenna systems, may be eliminated. As will be understood by those skilled in the art, a similar scheme may be used when telemetry signals and RF signals are to be transmitted from one or more T/R modules  104  to the driver stage  102  (as will be discussed in connection with FIG.  4 ). 
     FIG. 2 is a circuit diagram of the multiplexer  110  of the antenna system  100  shown in FIG.  1 . The preferred values of the components of the circuit  200  of FIG. 2 are indicated thereon; however, as will be understood by those skilled in the art, such values may be varied and equivalent components may be substituted therefor. 
     As mentioned above, the purpose of the multiplexer  110  (and, hence, the circuit  200 ) is to combine command signal  114 , DC power signal  116  and RF transmission signal  118 . The combined signal is to be provided to pin  202  (Combined Sig. Out) shown in FIG.  2 . In an effort to simplify the discussion of the circuit  200 , it will generally be discussed in sections. 
     Command Section 
     The command section is indicated by the components surrounded by the dashed lines identified by reference numeral  220 . The ultimate goal of the command section  220  is to provide an amplified, modulated control or command signal out of amplifier U 4 . 
     The combination of transistor Q 1 , resistor R 10 , diode D 3 , crystal oscillator Y 2 , capacitor C 23 , capacitor C 24  and resistor R 11  forms a Collpitts oscillator which oscillates at the crystal frequency of 10.7 MHz (although many other values are possible). A modulator which includes the aforementioned oscillator and an on-off keying circuit (comprised of resistor R 16 , resistor R 15 , capacitor C 5  and transistor Q 3 ) is provided. Because the oscillator takes a relatively long period to start up (approximately 1-2 milliseconds), the above-mentioned on-off keying circuit is provided, which improves the modulator&#39;s turn-on and turn-off times. Those skilled in the art will understand that other modulation formats may be substituted for the on-off keying (OOK) modulation described above. 
     Command data (i.e., the modulating signal), in the form of digital TTL level data, is provided to JP 4  via a microprocessor (not shown) or other conventional means. The command data is the modulating signal that is used to provide command signals which are supplied to T/R modules  104 . Thus, when the command signal is a “digital zero,” the collector of transistor Q 3  does not conduct to ground and allows the oscillator&#39;s signal to be provided to amplifier U 4 . Similarly, when the command signal is a “digital one,” the collector of transistor Q 3  grounds the oscillator&#39;s output to prevent the oscillator&#39;s signal from being provided to the amplifier U 4 . Accordingly, the command data signal is used as the modulating signal for the oscillator. 
     In case the oscillator is to be turned off (for example, to save power), rather than its output merely being shorted to ground, an oscillator enable/disable circuit is provided. Specifically, the oscillator enable/disable circuit includes transistor Q 2 , resistor R 13 , JP 2  and JP 1 . 
     By way of the oscillator and the on-off keying circuit (which is controlled via the command data signal), modulated control data is provided to amplifier U 4 . The main function of the amplifier is to amplify the modulated control data to improve signal to noise performance and ultimately generate an amplified, modulated command signal at its output. 
     DC Power Diplexer Section 
     The DC power diplexer section  230 , which is a combination of resistor R 17  and inductor L 4 , operates as a signal combiner. Thus, the DC power diplexer section is used to couple DC power from JP 3  with the amplified modulation signal. 
     RF Signal Combiner Section 
     The RF signal combiner section  240  includes capacitor C 6 , which operates as a DC blocker. (Alternative embodiments may include more elements in a πor T configuration, for example.) Thus, the RF signal from RF In is coupled to the amplified modulation signal and the DC power signal. Accordingly, the combination of all three signals are then provided at pin  202  (Combined Sig. Out). 
     FIG. 3 is a circuit diagram of the demultiplexer  112  of the antenna system  100  shown in FIG.  1 . The preferred values of the components of the circuit  300  of FIG. 3 are indicated thereon; however, as will be understood by those skilled in the art, such values may be varied and equivalent components may be substituted therefor. 
     As mentioned above, the purpose of the demultiplexer  112  (and, hence, the circuit  300 ) is to receive (via the RF feed network  106 ) the combined signal output from the multiplexer  110  and to separate the command signal  120 , DC power signal  122  and RF signal  124  from the combined signal. With reference to FIG. 3, the combined signal is received at pin  302  (Combined Sig. In). In an effort to simply the discussion of the circuit  300 , it will generally be discussed in sections. 
     RF Signal Section 
     The RF signal section  310  is used to separate the RF signal from the combined signal in. Capacitor C 3  operates as a DC blocker so that the DC power signal can only be conducted through inductor L 3 . Similarly, inductor L 3  blocks the RF signal from the DC power diplexer section  320  and command signal section  330 . This serves to minimize parasitic loading of the RF signal at pin  302 . Accordingly, inductor L 3  permits the amplified modulated signal (having a frequency of about 10.7 MHz) and the DC signal to pass. 
     DC Power Diplexer Section 
     The DC power diplexer section  320  is used to separate the DC power signal from the amplified modulated signal. The DC power diplexer section includes the combination of inductor L 2  and resistor R 4 . Furthermore, capacitor C 7  and capacitor C 8  are used to remove residual AC components from the DC power signal. 
     Command Signal Section 
     The command signal section  330  is used to recover the command signal. The signal remaining after the RF and DC power signals have been split off is provided to ceramic filter Y 1  to obtain an adequate signal-to-noise ratio. An envelope detector, formed by the combination of resistor R 1 , inductor L 1 , diode D 1  and capacitor C 1 , is used to detect the envelope of the modulated signal in order to recreate the digital data signal. Further, R 2  and C 2  form a low-pass filter which is used to remove residual high-frequency components from the envelope. Finally, the remaining signal is provided to an adaptive comparator circuit formed by the combination of diode D 2 , capacitor C 9 , resistor R 6  and resistor R 9 . Diode D 2  and capacitor C 9  are charged up to the peak of the envelope, while resistor R 2  and resistor R 9  are set to produce an output on pin  5  which is ⅔ of the peak, which operates as a reference for the comparator U 1 A. The other input to the comparator U 1 A is the detected signal on pin  4 . Thus, the detected signal on pin  4  is compared to an adaptive reference. Accordingly, even when signal levels are low, an accurate determination may be made for detection of a peak. The output of the comparator, on pin  4 , is the command signal. Thus, the RF signal, DC power signal and the command signal are all separated as identified by reference numerals  340 ,  350  and  360 , respectively. 
     FIG. 4 is a detailed block diagram of another embodiment, identified by reference numeral  400 , of the antenna system of the present invention. While FIG. 1 showed how command, DC power and RF signals could be combined and transmitted from the driver stage  102  to the T/R modules  104  (and then be separated), FIG. 4 shows (in addition to what is shown in FIG. 1) how telemetry and RF signals can be combined and transmitted from the T/R modules  404  to the driver stage  402 . 
     Thus, in a first mode, the antenna system  400  operates to combine ( 1 ) command, ( 2 ) DC power and ( 3 ) RF signals into a combined signal from the driver stage  402  to the T/R modules  404 , which combined signal is then separated into command, DC power and RF signals by the T/R modules  404 . Similarly, in a second mode, the antenna system  400  operates to combine ( 1 ) telemetry and ( 2 ) RF signals into a combined signal from a T/R module  404 , which combined signal is then separated into telemetry and RF signals at the driver stage  402 . As will be understood in the art, in order for both modes to be operable, both a multiplexer and demultiplexer are provided at each T/R module  404  and at the driver stage  402 . For convenience, however, (and to more clearly describe the invention) the multiplexer/ demultiplexer combination for the driver stage  402  is depicted as diplexer  410 . Likewise, the multiplexer/demultiplexer combination for each T/R module  404  is depicted as diplexer  412 . 
     As will also be understood by those skilled in the art, neither the multiplexer at each T/R module  404  nor the demultiplexer at the driver stage  402  includes a DC power diplexer (refer to FIGS.  2  and  3 ), since the DC power signal need only supplied from the driver stage  402  to each T/R module  404 . Accordingly, DC power is supplied to all of the active elements via its transmission from the driver stage  402  to each T/R module  404  in a manner that will be understood by those skilled in the art. 
     Referring again to FIG. 4, certain components (shown in block diagram form) will now be described to show how the antenna system  400  operates in both modes. Specifically, driver stage  402  includes a command generator  424 , a telemetry receiver  426 , a control line  428 , a switch  430 , a command signal conductor  432 , a telemetry signal conductor  434 , an RF signal conductor  436 , a combined command/telemetry conductor  438 , a DC power conductor  440  and the aforementioned diplexer  410 . 
     When command, DC power and RF signals are to be delivered to the T/R modules  404 , the command generator  424  generates a control signal on control line  428  which causes switch  430  (which, in a preferred embodiment, is in a default position that electrically connects the telemetry receiver  426  to the combined command/telemetry conductor  438  via telemetry signal conductor  434 ) to connect the command generator  424  to the combined command/telemetry conductor  438 . Thus, the command signal is provided to the diplexer  410 , where it is combined with the DC power and RF signals. The combined signal is then delivered across the RF feed network  450  via RF transmission lines  452  to all of the T/R modules  404 . 
     The T/R modules  404  include the aforementioned diplexer  412 , a T/R module select decoder  454 , a command receiver  456 , a telemetry generator  458 , a first control line  460 , a second control line  462 , a switch  464 , a command signal conductor  466 , a telemetry signal conductor  468 , an RF signal conductor  470 , a combined command/telemetry conductor  472  and a DC power conductor  474 . The demultiplexer  412  receives the combined signal and separates it into an RF signal, a command/telemetry signal and a DC power signal. The command signal is coupled to T/R module select decoder  454  via the combined command/telemetry conductor  472  and T/R module select decoder conductor  476 . The T/R module select decoder  454  determines whether the command data included in the command signal is intended for a particular T/R module  404 , since each T/R module  404  includes a unique electronic serial number or the like. More specifically, the T/R module select decoder  454  reads header information contained within the command signal (which includes, for example, an electronic serial number of a T/R module  404 ) to determine whether it is the intended recipient of the command data being broadcast via the RF feed network  450  by comparing the header information to its electronic serial number. As will be understood by those skilled in the art, the specific protocol may also include a method of delivering global commands or commands to a group of T/R modules. 
     If the T/R module select decoder  454  determines that the command data is intended for its particular T/R module  404 , the T/R module select decoder  454  generates a control signal on first control line  460 , which causes switch  464  to couple command receiver  456  with combined command/telemetry conductor  472  via command signal conductor  466 . The command receiver  456  receives the command data, interprets it and performs a function in response thereto (such as varying the phase of the RF signal delivered to antenna element  205 , in order to steer the beam of the antenna  400 ), as will be understood by those skilled in the art. 
     One of the functions that may be performed, based upon command data being provided to the command receiver  456 , is that telemetry information may be generated and provided from a particular T/R module  404  to the driver stage  402 . Such telemetry information may include, for example, the sensed temperature at a particular T/R module, internal voltages or currents, or many other operations-related (or non-operations related) parameters. 
     Thus, when a particular T/R module  404  is to be queried for specific telemetry information, command data is provided to such T/R module  404  as set forth above (wherein the command data specifies the particular telemetry information that is to be provided from the T/R module  404  to the driver stage  402 ). In response, the telemetry generator  458  generates a first control signal on second control line  462  which is received by T/R module select decoder  454 . A second control signal is generated on first control line  460 , which causes the switch  464  to couple the telemetry generator conductor  468  to the combined command/telemetry conductor  472  so that telemetry data may be forwarded to diplexer  412  and be combined with RF signal. The combined received signal is then fed to driver stage  402  via RF feed network  450 . 
     The combined signal is received by the diplexer  410  which separates the combined signal into a telemetry signal and an RF signal. The telemetry signal is coupled to the telemetry receiver  426  via combined command/telemetry conductor  438 , switch  430  and telemetry receiver conductor  434 . To identify the particular T/R module  404  from which the telemetry information is being provided, the telemetry signal includes a header associated with the T/R module  404  (e.g., its electronic serial number or the like). 
     FIG. 5 is a frequency plot showing the relative frequencies of the DC power signal, command/telemetry signal and RF signal for the antenna system of the present invention in a half-duplex configuration. As will be understood by those skilled in the art, a half duplex configuration permits either command data or telemetry data (but not both at the same time) to be transmitted between the driver stage  402  and T/R modules  404  (e.g., a walkie-talkie). Accordingly, in the half duplex configuration, the command data and telemetry data are intended to be modulated at the same frequency. As shown in FIG. 5, the RF signal has a relatively high frequency defined by high-pass filter HPF, the DC signal has a relatively low frequency defined by low-pass filter LPF and the command/telemetry signals have a carrier frequency which is in an intermediate frequency range defined by bandpass filter BPF. 
     FIG. 6 is a frequency plot showing the relative frequencies of the DC power signal, command signal, telemetry signal and RF signal for the antenna system of the present invention in a full-duplex configuration. As will be understood by those skilled in the art, a full-duplex configuration permits command data and telemetry data to be transmitted between the driver stage  402  and the T/R modules  404  at the same time (e.g., a conventional wireline telephone). Accordingly, in the full-duplex configuration, the command data and telemetry data are intended to be modulated at different carrier frequencies. As shown in FIG. 6, the RF signal has a relatively high frequency defined by high-pass filter HPF, the DC signal has a relatively low frequency defined by low-pass filter LPF, the command signal has a first intermediate frequency defined by first bandpass filter BPF 1  and the telemetry signal has a second intermediate frequency defined by second bandpass filter BPF 2 . 
     As will be understood by those skilled in the art, instead of using a single driver stage as shown in the drawings, multiple driver stages may be provided. Furthermore, as will also be understood by those skilled in the art, elimination of solely the DC power wire harness would be beneficial since the DC power wire harness (and its associated conductors) are generally quite heavy and costly in order to minimize power losses. Accordingly, the principles of the present invention may be used to eliminate solely the DC power wire harness, instead of both, wire harnesses. Finally, it should be noted that the advantages of the present invention may be useful for phased-array antenna systems that are not deployed in space and; therefore, scope of the present invention should not be limited to the particular embodiments described herein. 
     It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. For example, instead of providing power to the T/R modules via a DC signal, a low frequency AC signal (e.g., between 0-1000 Hz) may be used. Furthermore, it should be understood that telemetry information may be provided from the driver stage to one or more T/R modules. Even further, telemetry information may be generated automatically (after some predetermined time interval), instead of in response to a command signal from the driver stage. Finally, switch  464 , command receiver  456 , decoder  454 , telemetry generator  458  and line  466  could all exist in a single microcontroller, since they are simply functional entities and may be embodied in a variety of ways. 
     The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not intended to be limited to the details given herein.