Abstract:
A solid state active aperture high power polarization agile transmitter, either single or dual polarization, employing nonreciprocal antenna elements, designed such that it can be used in an Electronic Warfare system that is more efficient and less expensive. Antenna beam steering is accomplished with variable phase shifters that are used to set the RF signal phase of each element. The beam steering function is implemented with a hardware architecture where the phase shifters are built-in ahead of the power amplifiers such that these low power phase shifters impart phase delays to low power signals without wasting RF signal power and hence improving efficiency. These power transmitter devices are also more reliable, lighter in weight and smaller in size.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to radar and Electronic Warfare (EW) systems, in particular to high power transmitters used in these systems. 
     RELATED APPLICATIONS 
     This application is related by subject matter to the application Ser. No. 10/097,408 entitled “Array Antenna Beam Steering Architecture”, filed in the name of inventors Martin J. Apa, Joseph Cikalo, William L. High and Mitchell J. Sparrow. 
     BACKGROUND OF THE INVENTION 
     Electronic Warfare (EW) generally relates to military action involving the use of electromagnetic and directed energy to control the electromagnetic spectrum or to attack the enemy. The three major subdivisions within EW are Electronic Attack, Electronic Protection, and Electronic Support. Electronic Attack (EA) is the division of EW involving the use of electromagnetic or directed energy to attack personnel, facilities or equipment with the intent of degrading, neutralizing or destroying enemy combat capability. There is a great need for transmitters used in an EW system to be small in size, low in weight, and able to carry many watts/cubic inch. In addition, there is often a need in EW systems for a higher power transmitter that is also polarization agile. 
     One objective of an EW system may be to produce a jamming signal (e.g. false targets) in a threat radar receiver that is much greater in amplitude than that of the radar signal reflected by the target aircraft, with the appropriate polarization. The availability of advanced power amplification technologies makes it possible to develop high power transmitters with the above characteristics. 
     The basic architecture of such a transmitter is an active aperture antenna consisting of a large number of elements. Though the output power of each antenna element is a relatively low level, a high power Radio Frequency (RF) signal is obtained by combining the individual signals in space. To attain the highest power levels, a phase focusing technique is employed. Each element is tuned to produce a signal with the appropriate phase in order to spatially combine. However, phase focusing also produces a narrow beam antenna. Consequently, a beam steering network is used in order to radiate the maximum transmitted signal in a desired direction. Generally, a beam steering network may comprise a network having variable phase shifters, time delay elements or fiber optic delays with an external processor and drivers to adjust them. 
     Conventionally, the phase shifters are inserted at the output terminal of the system&#39;s power amplifiers, just prior to feeding the RF radiators. A significant drawback of this architecture is that a large amount of RF power is dissipated in the phase shifters placed after the power amplifiers. This reduces the efficiency of the system and requires additional cooling system capability. Moreover, dissipation of a large amount of RF power in such an architecture generally requires use of large, less reliable high power phase shifters that must be capable of handling high RF power levels. The requirement for large size phase shifters makes such transmitter systems used in EW equipment more bulky, less accurate, and less agile. These are significant drawbacks. 
     Also, when such a transmitter is installed on an mobile vehicle, such as an aircraft, it is necessary that as the mobile vehicle changes direction, the phase shift entered by the beam steering network is also changed. To effectively focus the narrow beam in the direction of the threat radar, it is important to monitor the direction of the incoming signal from the threat radar and adjust the phase shift effected by the beam steering phase shifters. In open loop systems, typically no adjustment is provided regarding the difference between the direction of the incoming signal and the direction of the transmitted signal. This can undermine the effectiveness of the radar jamming capability. 
     Other problems and drawbacks also exist. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention comprises a polarization agile transmitter module with a closed loop architecture. The polarization agile transmitter module includes a beam steering phase shifter module, a power amplifier module, an antenna module, a transmit polarimeter, a receive polarimeter, a null adaptive tracker, and a direction finding phase shifter module, where the beam steering phase shifter module is located before the power amplifier module. 
     According to another aspect of the invention, an electronic counter-measure (ECM) signal is inputted into the beam steering phase shifters. 
     According to another aspect of the invention, the direction finding (DF) phase shifter module measures the difference in the direction of the signal received by the antenna module and the direction of the signal transmitted by the antenna module. 
     According to yet another aspect of the invention, the phase shift entered by the beam steering phase shifter module is changed based upon the difference in the direction of the signal received by the antenna module and the direction of the signal transmitted by the antenna module, as measured by the DF phase shifter module. 
     According to another aspect of the invention, the receive polarimeter measures the polarization parameters of the signal received by the antenna module. 
     According to yet another aspect of the invention, the transmit polarimeter adjusts the polarization of the signal transmitted by the antenna module based on the feedback received from the receive polarimeter regarding the polarization of the signal received by the antenna module. 
     According to another aspect of the present invention, multiple polarization agile transmitter modules are used with an array of antenna modules. 
     According to another aspect of the present invention, a summing network is provided with multiple polarization agile transmitter modules for summing the signal received by each of the multiple modules. 
     According to another aspect of the present invention, a direction finding (DF) receiver is provided for monitoring and processing of the directional information regarding the received signal. 
     According to yet another aspect of the present invention, a beam scanning module is provided to display the output signal from the DF receiver. 
     Accordingly, it is one object of the present invention to overcome one or more of the aforementioned and other limitations of existing polarization agile transmitter systems. 
     It is another object of the present invention to provide an efficient polarization agile transmitter using low power phase shifters. 
     It is yet another object of the present invention to provide a polarization agile transmitter that solves or mitigates the problems associated with the requirement of high power beam steering phase shifters. 
     It is another object of the present invention to provide a polarization agile transmitter that is smaller, lighter and more reliable. 
     It is yet another object of the present invention to provide a polarization agile transmitter capable of adjusting the direction of the transmitted signal based on the direction of the incoming signal. 
     It is yet another object of the present invention to provide a polarization agile transmitter capable of adjusting the polarization of the transmitted signal based on the polarization of the incoming signal. 
     The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. It will become apparent from the drawings and detailed description that other objects, advantages and benefits of the invention also exist. 
     Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the systems and methods, particularly pointed out in the written description and claims hereof as well as the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The purpose and advantages of the present invention will be apparent to those of ordinary skill in the art from the following detailed description in conjunction with the appended drawings in which like reference characters are used to indicate like elements, and in which: 
     FIG. 1 is a block diagram of a polarization agile transmitter module according to an embodiment of the invention. 
     FIG. 2 is a block diagram of an EW subsystem containing multiple polarization agile transmitter modules according to an embodiment of the invention. 
    
    
     To facilitate understanding, identical reference numerals have been used to denote identical elements common to the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a block diagram of an embodiment of the present invention. According to this embodiment, ECM signal  100  is a radio frequency (RF) signal, generally obtained from the signal transmitted by the threat radar and received by a receiving antenna located on the target vehicle and possibly stored by a system external to the one described here. Such an ECM signal  100  contains information regarding the direction in which the signal should be transmitted to block the threat radar. A similar signal  610  will also be received by the antenna module  600 . The antenna module  600  directs the received signal  610  to circulators  500 . Circulators  500  are operatively connected to the direction finding (DF) phase shifter modules  700  via switches SW 1   651  and SW 3   653 . Switches SW 1   651 , SW 3   653 , SW 2   754  and SW 4   752  straddle the DF phase shifter modules  700  such that they can either route the signal from circulators  500  around the DF phase shifter modules  700  or cause the signal from circulators  500  to pass through the DF phase shifter modules  700 . The outputs from switches SW 2   754  and SW 4   752  are inputted into the receive polarimeter  800 . The outputs from the receive polarimeter  800  are inputted into the null adaptive receiver tracker  900 . The null adaptive receiver tracker  900  outputs control signals that are inputted into the beam steering phase shifter module  200 , the transmit polarimeter  300 , the receive polarimeter  800 , and the DF phase shifter modules  700 . ECM signal  100  is inputted into the beam steering phase shifter module  200 . The output from the beam steering phase shifter module  200  is inputted into the transmit polarimeter  300 . The outputs of the transmit polarimeter  300  are inputted into the power amplifier modules  400 . The output signals from the power amplifier modules  400  are inputted into the circulators  500 . The circulators  500  direct the signals to antenna module  600 . 
     The ECM signal  100  input into the beam steering phase shifter module  200  is a radio frequency (RF) signal, generally obtained from the signal transmitted by the threat radar and received by a receiving antenna located on the target vehicle. This signal  100  is delayed by nψ degrees which causes a corresponding delay of the output signal of the n-th phase shifter in phase shifter module  200  by nψ degrees, where nψ is the phase shift effected by the n-th phase shifter. The ECM signal  100  should be fed in parallel to all of the n beam steering phase shifters in the phase shifter module  200 . The beam steering phase shifter module  200  also receives a signal from the null adaptive receiver tracker  900  (the functioning of the null adaptive receiver tracker  900  is described in detail below). The phase shift nψ effectuated by each of the phase shifters in the phase shifter module  200  is controlled by the signal received from the adaptive null receiver tracker  900 . As a result of the phase shifts caused by each of the phase shifters in the phase shifter module  200 , the ECM signal, when inputted into the antenna module  600 , generates a beam spatially focused in the desired direction. The implementation of the phase shifter module  200  to effect a beam focused in the desired direction is well known to those of ordinary skill in the art. 
     The beam steering phase shifter module  200  may comprise loaded line phase shifters, switched line phase shifters, hybrid-coupled phase shifters, or any other suitable device for phase shifting. Beam steering phase shifter module  200  may comprise any of the various types of phase shifters available such as transistor/diode phase shifters, FET phase shifters, GaAs Monolithic Microwave Integrated Circuit (MMIC) phase shifters, or other suitable phase shifters. In one embodiment of the present invention, low power and low cost MMIC phase shifters are used. 
     According to an embodiment of the present invention, the output of the beam steering phase shifter module  200  is inputted into a transmit polarimeter  300 . The design and operation of an exemplary transmit polarimeter  300  is provided in U.S. Pat. No. 4,937,582 to Mohuchy, incorporated herein by reference in its entirety. The transmit polarimeter  300  also receives a signal from the null adaptive receiver tracker  900 . The transmit polarimeter  300  generates orthogonal polarization components of the signal to be transmitted by antenna module  600 . The transmit polarimeter  300  varies its output until the signal received from the null adaptive tracker  900  matches the signal inputted into the transmit polarimeter  300 . The implementation of the transmit polarimeter  300  is well known to those of ordinary skill in the art. 
     The output signals from the transmit polarimeter  300  are input into the power amplifier modules  400 . Each power amplifier module  400  amplifies the orthogonal polarization components before they are passed to and transmitted by the antenna module  600 . The power amplifier modules  400  may be designed using a suitable technology, such as GaAs, GaN, SiC, InGaN or AlGaN MMIC chip or Microwave Power Modules (MPM) technology. In one embodiment of the invention, the power amplifier modules  400  make use of advanced power amplification technologies that use GaAs MMIC chips. Implementation of suitable power amplifiers for power amplifier modules  400  is well within the skill of the ordinary artisan. 
     The output signal phase of the antenna module  600  has two components, the set-on phase shifter phase (nψ) and a phase error δφ n , a phase error of the n-th power amplifier. The composite phase value of the antenna output is not dependent on the phase shifter&#39;s location in relation to the power amplifier&#39;s location in the circuit feeding antenna module  600 . Hence, placing the phase shifter module  200  before the power amplifier modules  400  should not adversely affect the phase error of the output signal phase. 
     The implementation of the invention as suggested here with the power amplifier modules  400  following the beam steering phase shifter module  200  results in an efficient design that provides advantages over the conventional approach of designing beam steering for a polarization agile transmitter. It has been shown that the beam steering function can be as well instrumented with the phase shifter module  200  placed before the power amplifier modules  400 , as compared to the conventional approach, where the phase shifters are placed at the output of the power amplifier module. According to simulation modeling of an embodiment of the present invention, beam steering accuracy achieved by this approach is comparable to that achieved by the traditional approach. Specifically, the phase error performance in the beam steering function is maintained for the invention as compared to the conventional approach. Additionally, placing the phase shifter module  200  before the power amplifier modules  400  allows power amplifier modules  400  to compensate for any signal attenuation occurring in phase shifter module  200 . In sum, the performance of the beam steering function is maintained while providing a number of significant advantages. 
     Continuing with FIG. 1, the amplified output signals from the power amplifier modules  400  are inputted into the circulators  500 . A circulator, in its basic form, is a three port device formed by a symmetrical Y junction coupled to magnetically-biased ferrite material. A circulator permits flow of RF energy in one direction only, e.g., from port  1  to  2 ,  2  to  3 , and  3  to  1 . According to an embodiment of the invention, port  1  to  2  of circulators  500  is used to allow flow of the amplified RF signal outputs inputted from the power amplifier modules  400  to the antenna module  600 ; port  1  to  3  of the circulators  500  is used to allow flow of the amplified RF signal outputs from the power amplifier modules  400  to switches SW 1   651  and SW 3   653 ; and port  2  to  3  of the circulators  500  is used to allow flow of the signals received by the antenna module  600  to the switches SW 1   651  and SW 3   653 . This or other equivalent implementations of the circulator are well within the skill of the ordinary artisan in the art. 
     The antenna module  600  may be comprised of specialized transducers that convert RF fields into AC signals or vice-versa. Implementation of antenna module  600  and its coupling to a circulator  500  is well within the skill of the ordinary artisan. In one embodiment of the present invention, Vivaldi Flare Notch Radiator type transducers are used in antenna module  600  to transmit and receive RF signals. The RF signals from the power amplifier modules  400  that are fed into the antenna module  600  via the circulators  500  are converted to an RF field and transmitted in the direction of the threat radar. The antenna module  600  also receives the signal from the threat radar and converts it into an electrical signal. Port  2 - 3  of circulator  500  enables the flow of the signal received by the antenna module  600  to switches SW 1   651  and SW 3   653 . 
     In an embodiment of the invention, switches SW 1   651  , SW 3   653 , SW 2   754  and SW 4   752  are implemented such that the polarization agile transmitter works in two separate modes, the first being the transmit mode and the second being the receive mode. In the transmit mode, the port  1 - 2  of the circulators  500  directs the flow of amplified signals from the power amplifier modules  400  to antenna module  600 , while port  1 - 3  of the circulators  500  directs the signal outputs from the power amplifiers modules  400  to the switches SW 1   651  and SW 3   653 . During the transmit mode, switches SW 1   651 , SW 3   653 , SW 2   754  and SW 2   754  are operated in a self-test mode such that most of the signal received by switches SW 1   651  and SW 3   653  is bypassed around the DF phase shifter modules  700 . Only a low level of the power amplifier module  400  output signal is passed through the DF phase shifter modules  700 . DF phase shifter modules  700  measure the phase of the signal received from the corresponding power amplifier module  400  that is transmitted by the antenna module  600 . As a result, in the transmit mode, most of the signal that is inputted into the switches SW 1   651  and SW 3   653  is bypassed to switches SW 2   754  and SW 2   754 , and then to the receive polarimeter  800 . 
     In the receive mode of the polarization agile transmitter, the signals generated by the antenna module  600  are directed by port  2 - 3  of the circulators  500  to switches SW 1   651  and SW 3   653 . In this mode, the switches SW 1   651  and SW 3   653  are enabled to pass the signals to the DF phase shifter modules  700 . Each of the DF phase shifter modules  700  measures the phase of the signal received by the antenna module  600 . Since the amplified signal output from the power amplifier module  400  is much larger in amplitude than the signal received by the antenna module  600 , only a small fraction of the signal output from power amplifier module  400  is directed to DF phase shifter modules  700 . 
     Thus, switches SW 1   651 , SW 3   653 , SW 2   754  and SW 4   752  serve the function of gating the transmitted as well as the received signal around the DF phase shifter modules  700 . As a result of this arrangement using the switches SW 1   651 , SW 3   653 , SW 2   754  and SW 4   752 , it is possible to use smaller and lower power phase shifters in DF phase shifter modules  700 . In an embodiment of the present invention, GaAs MMIC type phase shifters are used as DF phase shifters  700 . 
     In DF phase shifter module  700 , the phase of the signal received by the antenna module  600  is compared with the phase of the signal output by the power amplifier module  400 . The information regarding the difference in phase between the two signals is used as a feedback to adjust the phase shifts effected by the beam steering phase shifter module  200 . This feedback mechanism serves the important purpose of ensuring that the phase shifts entered by the beam steering phase shifter module  200  are such that the signal output from the antenna module  600  creates a beam directed towards the threat radar system. Preferably, the DF phase shifter module  700  continuously compares the phase of the signals transmitted by the antenna module  600  with the phase of the signal received by the antenna module  600 . The implementation of DF phase shifter module  700  is well known to those of ordinary skill in the art. 
     The signals outputted from the switches SW 2   754  and SW 4   752  are inputted into the receive polarimeter  800 . The receive polarimeter  800  resolves the signals received by the antenna module  600  into two substantially orthogonal polarized signals and measures the polarization of each component. The design and operation of an exemplary receive polarimeter  800  is provided in U.S. Pat. No. 4,937,582 to Mohuchy, incorporated herein by reference in its entirety. The polarization information about the received signal is inputted into the null adaptive receiver tracker  900 . 
     Null adaptive receiver tracker  900  operates according to the well known principle that any polarization can be generated with two orthogonally disposed antennas whose amplitude and phase can be adjusted to the desired values. In analyzing the signal received from the receive polarimeter  800 , null adaptive tracker  900  undergoes a null adaptive algorithm analysis which is well known to those of ordinary skill in the art. An example of such analysis is a null adaptive algorithm used for mono-pulse detection schemes well known in the art. Based on the two orthogonally polarized signals received from the receive polarimeter  800 , the null adaptive receiver tracker  900  develops a series of control signals to set the desired polarization and phase of the signal transmitted by antenna module  600 . In an embodiment of the present invention, the null adaptive receiver tracker  900  uses a digital signal processor (DSP) to analyze the orthogonally polarized signal and to develop a series of control signals. These control signals are inputted into the transmit polarimeter  300  to set the polarization of the signal to be transmitted by the antenna module  600 . The control signals from the null adaptive tracker  900  are also inputted into the beam steering phase shifter module  200  to control the phase shift effected by such phase shifters. The design and operation of an exemplary null adaptive tracker  900  is provided in U.S. Pat. No. 4,937,582 to Mohuchy. 
     The implementation of the phase shifter module  200  in the disclosed configuration allows for the use of low power MMIC phase shifters. This approach results in increased efficiency derived from the reduction of RF signal power dissipation, greater mean time between failures (MTBF) and lower overall cost for polarization agile transmitter. These are very significant benefits. 
     The skilled artisan will readily appreciate that embodiments of the present invention may be fabricated using technologies which include those in which all components described above can be in analog or in digital chip form and which can be integrated in compact modules. For example, due to reduced RF power dissipation in phase shifter module  200 , one can utilize GaAs MMIC such as coplanar GaAs waveguides. This provides a means for obtaining the advantage of small size and reduced manufacturing costs from these technologies in an ECM system. According to an embodiment of the present invention, magnitude reduction in the range of about 10:1 compared to traditional design can be achieved. In addition, the aspect of the present invention which makes it possible to utilize the solid state technology also makes it practical to utilize these technologies to provide phased array applications which were hitherto prohibitively expensive. 
     The embodiment of the present invention as described in FIG.  1  and explained above creates a complex module (also referred to as a “mini-jammer”) that has the capability to adaptively track the polarization and direction of a threat radar signal using the concept of “measure and match,” and to set and control the polarization and phase of its own output signal. In a typical ECM system a number of such modules may be implemented with an array of antennas, where each module is coupled to an antenna in order to receive and to radiate its own output signal. 
     FIG. 2 shows an embodiment of two modules of the present invention connected with two antennas. In practice, such a system can be made up of a number of modules, such as for n=2, 3 and so on. For purposes of illustration, an ECM system with two modules is shown in FIG.  2 . Each module receives an ECM signal input from the source  100 . The ECM signal is inputted into beam steering phase shifter modules  200 . The function of the beam steering phase shifter modules  200  is as described above in FIG.  1 . The output signals from each of the beam steering phase shifter modules  200  are input into the transmit polarimeters  300 , which function as described in FIG. 1 above. The output signals from the transmit polarimeters  300  are input into the power amplifier modules  400 . The amplified output from the power amplifier modules  400  are input into the circulators  500 . The circulators  500  performs the function of routing the signals between the power amplifier modules  400 , the antenna modules  600 , and the direction finding phase shifter modules  700  as explained in FIG.  1 . The circulator modules  500  are connected to the DF phase shifter modules  700  using switches SW 1  and SW 3  as described in FIG. 1 (for simplicity, the switches SW 1 , SW 2 , SW 3  and SW 4  straddling the DF phase shifters of each module are not shown in the FIG.  2 ). The DF phase shifter modules  700  compare the phase of the transmitted signal with the phase of the incoming signal as described in FIG.  1 . The outputs from the DF phase shifter modules  700  are inputted into the receive polarimeters  800 . The receive polarimeters  800  analyze the polarization of the incoming signals to generate control signals as explained in FIG.  1 . The receive polarimeters  800  are connected to the null adaptive trackers  900 . The design and operation of the null adaptive trackers  900  is as described in FIG.  1 . 
     In an embodiment of the present invention, the output signals from the receive polarimeters  800  are inputted into a summing network module  1000 . The summing network module  1000  sums the signal received from each of the individual receive polarimeters  800 . Since the signal received by each of the antenna modules  600  is part of a vector, the summing of signals received from each of the antenna modules  600  recreates the complete waveform incident upon the array of antenna modules  600 . The design and implementation of such summing network  1000  is well known to those of ordinary skill in the art. 
     In an embodiment of the present invention, the signal output from the summing network  1000  is inputted into the DF receiver module  1100 . Generally, DF receiver module  1100  includes a central processing unit (CPU) and other input-output modules to allow for the automatic monitoring and processing of directional information regarding received signals. The implementation of such a DF receiver module  1100  is well within the skill of the ordinary artisan. In an embodiment of the present invention, the output from the DF receiver module  1100  is inputted into the beam scanning module  1200 . Beam scanning module  1200  allows the display of the output signal from the DF receiver module  1100  on a cathode ray tube (CRT) or other kind of monitor. This allows manual monitoring of the directional information regarding the received signal. The implementation of this beam scanning capability is well known to those of ordinary skill in the art. 
     As it should be clear, further embodiments of the present invention may be made without departing from its teachings and all such embodiments are considered to be within the spirit of the present invention. For example, although preferred embodiments of the present invention comprises MMIC phase shifters, it should be clear to those of ordinary skill in the art that embodiments of the present invention may be comprised of FET phase shifters as well. Also, although the invention has been described in embodiments used principally in military applications, it should be understood that the invention may be applied in non-military commercial and civilian applications. Therefore, it is intended that all matter contained in above description or shown in the accompanying drawings shall be interpreted as exemplary and not limiting, and it is contemplated that the appended claims will cover any other such embodiments or modifications as fall within the true scope of the invention.