Abstract:
Embodiments of a switchable high-power transmit module to selectively provide a high-power microwave signal in excess of one kilowatt to one of first and second output paths are disclosed herein. The module includes a switch to receive a lower-power microwave signal from a source, a first ninety-degree coupler for directing power from the switch to first and second paths, a first high-power amplifier disposed in the first path, a second high-power amplifier disposed in the second path, and a second ninety-degree coupler to receive output signals of the first and second amplifiers. The switch is configured to selectively couple the lower-power microwave signal between first and second input ports of the first ninety-degree coupler. When the switch couples the lower-power microwave signal to a selected one of the input ports of the first coupler, signals generated by the first and second high-power amplifiers are combined in the second ninety-degree coupler to provide the high-power microwave output signal on only one of the output paths.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to antenna systems. More specifically, the present invention relates to high power microwave antennas, arrays thereof and components therefor. 
   2. Description of the Related Art 
   High power microwave antennas are being considered for various area defense applications such as airport protection. For such applications, a high power microwave beam is to be directed to an incoming missile for the purpose of disrupting and confusing the guidance system of the missile to render it incapable of completing its mission. For an airport application, the system would be required to protect aircraft landing and taking off along the airports runway(s). Hence, at least two phased array systems are required, one for each runway direction (180 degrees apart). 
   Other airport configurations may have multiple runways oriented perpendicularly from each other. These airports could require 3 or 4 phased array systems to protect aircraft in the takeoff and landing scenarios for each runway. Such an airport protection system would be expensive using conventional teachings. The addition of multiple phased array antenna systems will probably make the approach infeasible for airport protection. 
   Moreover, for the illustrative area defense and other applications, it is necessary or desirable to transmit a considerable amount of energy at a high power level. Unfortunately, the switching of microwave energy at high power levels is problematic and poses a significant cost constraint on any system attempting to do so. 
   Hence, a need exists in the art for a system or method for irradiating and/or receiving microwave energy at high power levels in large volumes at low cost. 
   SUMMARY OF THE INVENTION 
   The need in the art is addressed by the systems and methods of the present invention. In a most general implementation, the inventive system is a module having a first coupler for directing power from a source to first and second paths; a first amplifier disposed in the first path; a second amplifier disposed in the second path; and a second coupler for combining the outputs of the first and second amplifiers. 
   In a more specific implementation, the module further includes a switch connected to the first coupler. The switch is a single-pole double throw switch. Each coupler is a 90-degree coupler that provides the combined energy output by each amplifier to a first or a second output port based on the position of the switch. The first coupler has first and second inputs, each input connected to a throw of the switch. The inclusion of a variable phase shifter allows for the module to be used to drive an element of a phased array antenna. 
   For high power applications, multiple such inventive modules may be used to drive the elements of one or more phased arrays pointed in different directions to provide a desired coverage pattern. In this application, in accordance with the present teachings, each module is adapted to switch energy at low power levels to drive one or more apertures with microwave energy at high power levels, that is, at a power level in excess of one kilowatt. The modules can also be configured as receive only or with circulators as transmit/receive modules. 
   The inventive method provides a technique for switching power at high levels to and from phase array and other antennas and a technique for providing area coverage using multiple phase array antenna arrangements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1(   a ) is a perspective view of a multiple aperture phase array antenna system implemented in accordance with an illustrative embodiment of the present teachings. 
       FIG. 1(   b ) is a magnified view of a portion of the antenna of  FIG. 1(   a ). 
       FIG. 1(   c ) is an alternative embodiment of the antenna depicted in  FIG. 1(   b ) 
       FIG. 2  is a simplified schematic diagram showing an illustrative implementation of a module in accordance with a first embodiment of the present teachings. 
       FIG. 3  is simplified schematic diagram of a transmit/receive module implemented in accordance with the present teachings. 
       FIG. 4  is a simplified perspective view of an illustrative three-aperture implementation of the present teachings. 
       FIG. 5  is a simplified schematic diagram of a transmit module adapted for the three-aperture system of  FIG. 4 . 
       FIG. 6  is a simplified perspective view of an illustrative four-aperture implementation of the present teachings. 
       FIG. 7  is a simplified schematic diagram of a transmit module adapted for the four-aperture system of  FIG. 6 . 
   

   DESCRIPTION OF THE INVENTION 
   Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
   While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
   As mentioned above, the use of microwave radiation for airport protection imposes a requirement on a phased array system to point in 180 degree opposing directions along an airport runway. Under normal circumstances this could be accomplished by constructing two separate phased array apertures, one for each direction. Such a system is disclosed and claimed in copending U.S. patent application Ser. No. 11/423,520 entitled ANTI-MISSILE SYSTEM AND METHOD, filed Jun. 12, 2006 by Kenneth W. Brown et al. , the teachings of which are hereby incorporated herein by reference. For the illustrative application, this may be cost prohibitive due to the enormous average power output requirement from each transmit module. 
   In accordance with the present teachings, a more cost effective solution is disclosed in which two (or more) phased array apertures share the same transmit module. This is illustrated in  FIG. 1 . 
     FIG. 1(   a ) is a perspective view of a multiple aperture phase array antenna system implemented in accordance with an illustrative embodiment of the present teachings. 
     FIG. 1(   b ) is a magnified view of a portion of the antenna of  FIG. 1(   a ). As illustrated in  FIGS. 1(   a ) and ( b ), in accordance with the present teachings, two apertures  12  and  14  (pointing 180 degrees apart) and mounted on a support structure  16 . The arrangement of  FIG. 1  is adapted to provide coverage in a separate direction. 
   The apertures  12  and  14  are fed by the same transmit module  20 . The transmit module  20  is paired with an antenna element  22  on the first aperture or array  12  and a second antenna element  24  on a second array  14 . 
     FIG. 1(   c ) is an alternative embodiment of the antenna depicted in  FIG. 1(   b ) in which the transmit module  20  is mounted behind one of the arrays  14 . In this case, the module  20  feeds an array element  22  on the first array  12  with a coaxial cable. In any event, in the illustrative application, the elements are fed with high power (i.e., in excess of 1 kilowatts) at microwave frequencies via an RF cable  26 . 
   Hence, for the intended application, the T/R module should be capable of switching its output between the two different antenna elements. This is problematic due to the high output power required for the illustrative area defense application and the need to provide switching therefor. In this application, each transmit module may be required to radiate energy at power levels exceeding 1 kilowatts of continuous wave energy. It is currently very difficult to obtain or design a switch that is capable of handling these power levels and even if it were possible, the cost would be prohibitively high. In addition, the high power switch would probably be mechanical in nature making it extremely difficult if not impossible to rapidly switch the phased array beam from one antenna aperture to the next, which may be important for some applications such as airport protection by way of example. In accordance with the present teachings, an inventive switching arrangement is disclosed to address this problem. The inventive arrangement is shown in  FIG. 2 . 
     FIG. 2  is a simplified schematic diagram showing an illustrative implementation of a module in accordance with a first embodiment of the present teachings. As shown in  FIG. 2 , a switchable high power transmit module  20  is configured utilizing a low power switch  30 . In accordance with the invention, the switch is a single-pole, double-throw switch connected to couple energy from a conventional variable phase shifter  28  to a first 90 degree coupler  32  via the throws (A) and (B) thereof. The switch  30  is selected based on the power, frequency and switching speed requirements of a given application. In the illustrative application, the switch  30  is selected to handle power on the order of milliwatts with a switching speed on the order of microseconds. The first coupler  32  may be a low power coupler etched onto a circuit board or purchased as a discrete component from a manufacturer such as Anaren by way of example. The coupler receives an input at one port and distributes the signal to each of two output ports thus providing two paths. In each path, an amplifier  34  or  36  is disposed. In the illustrative application, the amplifiers are high power microwave amplifiers. 
   In  FIG. 2 , the amplifiers output to a second 90-degree coupler  38 . In the illustrative application, the second coupler  38  is a high power coupler adapted to handle power at much higher levels (e.g. kilowatts) compared to the first coupler  32 . 
   The second coupler  38  is connected in a reverse direction relative to the first coupler  32  such that energy received at each port is combined and provided on a single output port. Hence, when the switch  30  is at position ‘A’, the combined outputs of the two amplifiers are fed to antenna element  22  on the first aperture  12  ( FIGS. 1(   a ) and ( b )) via the second coupler  38 . Likewise, when the switch  30  is at position ‘B’, the combined outputs of the two amplifiers are fed to antenna element  24  on the second aperture  14  ( FIGS. 1(   a ) and ( b )) via the second coupler  38 . 
   Consequently, the arrangement of  FIG. 2  is adapted to switch energy at low power (on the order of milliwatts) between the inputs of the first 90-degree coupler  32 . The 90-degree coupler  32  then feeds two power amplifiers  34  and  36 . In the inventive concept, the power amplifiers may be solid state and preferably with high gains (e.g., 60 dB). The two power amplifiers then feed an output 90-degree coupler. Depending on the selected leg of the input coupler, the output power re-combines in only one of the two outputs. Therefore, high power switching in accomplished with a low power switch. 
   Note that the drawback of the above technique (shown in  FIG. 2 ) is that two power amplifiers are required. However, for high power solid-state systems this is not typically a problem since multiple parallel power stages are often needed to get the desired power output. These multiple stages can be broken up into two separate power amplifiers as shown in  FIG. 2  without significantly increasing the cost and complexity of the transmit module. 
   As illustrated in  FIG. 3  below, the present teachings are not limited to a transmit only implementation. 
     FIG. 3  is simplified schematic diagram of a transmit/receive module implemented in accordance with the present teachings. In this module  20 ′, first and second circulators  39 ′ and  41 ′ are included to direct signals received by the radiating elements  22 ′ and  24 ′ to first and second low noise amplifiers  35 ′ and  38 ′. Additional switches  31 ′ and  33 ′ provide for transmit and receive switching modes. In the receive mode, the outputs of the receive amplifiers  35 ′ and  37 ′ are fed through the first coupler  32 ′ and the first switch  30 ′ to the variable phase shifter  28 ′. 
   Further, the present invention is not limited to the two-aperture implementation of  FIG. 1 .  FIG. 4  is a simplified perspective view of an illustrative three-aperture implementation of the present teachings. This arrangement provides coverage in three separate directions. 
     FIG. 5  is a simplified schematic diagram of a transmit module adapted for the three-aperture system of  FIG. 4 . As shown in  FIG. 5 , the phase shifter  28  feeds the first switch  30  as per the previous embodiments. A second low power switch  29  is added between the first switch and a first of two input couplers  32 . The first coupler  32  is supplemented with second, third and fourth input side couplers  42 ,  44  and  46 . The second coupler  42  is fed by the first switch  30  via one of the two throws thereof. The second coupler  42  has one side terminated with a resistor  25 . The first and second couplers  32  and  42  each provide an input to the third and fourth couplers  44  and  46 . The output ports of the third and fourth couplers  44  and  46  feed first, second, third and fourth power amplifiers  34 ,  36 ,  48  and  50 . The outputs of the first, second, third and fourth power amplifiers  34 ,  36 ,  48  and  50  feed the input ports of fifth and sixth couplers  52  and  54 , each of which, in turn, provide an input to both the seventh and eighth couplers  53  and  55 . The two outputs from one output coupler (e.g.  53 ) and one output from the other output coupler (e.g.  55 ) feed the three apertures (phased arrays) depicted in  FIG. 4 . 
     FIG. 6  is a simplified perspective view of an illustrative four-aperture implementation of the present teachings. This arrangement provides coverage in four separate directions. 
     FIG. 7  is a simplified schematic diagram of a transmit module adapted for the four-aperture system of  FIG. 6 . This module  60  may be identical to the module  40  of  FIG. 5  with the exception that a third input switch  27  is added, the resistor  25  is replaced with a connection to a throw of the switch  27  and the resistor  56  that terminates the second port of the output coupler  55  in  FIG. 5  is removed and the port is connected to the fourth aperture depicted in  FIG. 6 . 
   In accordance with the present teachings, the transmit modules depicted in  FIGS. 5 and 7  may be implemented as receive or transmit and receive modules per the teachings of  FIG. 3 . 
   Beam steering may be effected in a conventional manner using the arrangement such as that shown in the above-referenced copending U.S. patent application Ser. No. 11/423,520 entitled ANTI-MISSILE SYSTEM AND METHOD, filed Jun. 12, 2006 by Kenneth W. Brown et al. 
   Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications applications and embodiments within the scope thereof. 
   It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
   Accordingly,