Abstract:
A microwave parametric amplifier uses a circulator to receive an input signal which is provided through a transfer port to an input signal resonant cavity. A pump signal, which is preferably a harmonic of the input signal, is received into a pump signal cavity which is defined by a barrier that is reflective to the pump signal and transmissive to the input signal. A non-linear medium is positioned within the pump signal cavity to produce carriers due to the energy of the pump signal. The input signal interacts with the carriers to produce an amplified input signal which is conveyed from the input signal cavity through the circulator to an output port of the circulator.

Description:
BACKGROUND OF THE INVENTION 
     In certain fields of use, such as missiles and aircraft, microwave energy is utilized for such purposes as radar and communication. However, as greater levels of energy are needed for these signals, problems of weight, volume and expense are encountered for the electronic equipment needed to produce the required signals. Further, there are limitations for the amount of power available for the generation of these signals. Thus, there exists a need for methods and apparatus to produce microwave signals at desired energy levels by using as little energy and hardware as possible. 
     SUMMARY OF THE INVENTION 
     A selected embodiment of the present invention is a microwave parametric amplifier which includes a housing having an interior cavity. A circulator is connected to the housing. The circulator has an input signal port for receiving an input signal, an output signal port and a bidirectional transfer port which is coupled to the interior cavity of the housing. A pump signal port is coupled to the interior cavity of the housing for receiving a pump signal. A non-linear medium is positioned within the interior cavity for receiving the pump signal and thereby liberating carriers within the medium. A frequency selective barrier within the interior cavity substantially reflects the pump signal and is substantially transparent to the input signal. The frequency selective barrier defines a pump signal resonant cavity within the housing interior cavity. An output signal is produced within the interior cavity as a result of interaction of the input signal and the carriers in the non-linear medium. The output signal is conveyed through the bidirectional port to the circulator and to the output port of the circulator. The output signal is an amplified version of the input signal having the same frequency as the input signal but at a greater amplitude. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a perspective, partially cut away view of a microwave parametric amplifier in accordance with the present invention, 
     FIG. 2 is a schematic diagram for the parametric amplifier shown in FIG. 1, and 
     FIG. 3 is a waveform chart for illustrating the operation of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A parametric amplifier  10  in accordance with the present invention is illustrated in FIG.  1 . The amplifier  10  receives an input microwave signal ω 1  which is amplified to produce an output signal at the same frequency. A microwave signal ω 3  is provided as a pump signal which is at a higher frequency than the input signal ω 1 . 
     The amplifier  10  includes a lower housing  12  and a top plate  14  which is secured to the housing  12  by means of screws  16 ,  18 ,  20  and  22 . Housing  12  and the plate  14  are preferably made of brass, aluminum or a plated dielectric material. The input signal ω 1  is provided to the amplifier  10  through an input wave guide  60  which is coupled to a circulator  62 . The circulator  62  is connected via a bidirectional signal transfer wave guide  64  to the plate  14 . An opening  66  in the plate  14  provides transfer for signals to and from the circulator  62 . An output wave guide  68  conveys the amplified output signal ω 1  from the circulator  62 . 
     The pump signal ω 3  is transmitted through a wave guide  74  and an opening  76  in the plate  14  to the interior of the amplifier  10 . 
     The dimensions of each of the wave guides shown in FIG. 1, as well as the dimensions of the amplifier  10 , are principally determined by the frequency of the input signal ω 1  and the pump signal ω 3 . The input and output wave guides are also referred to as input and output ports. 
     Within the housing  12  there is provided a grid structure comprising a plurality of layers of materials. At the top of the grid there is provided a nonlinear layer  38 . Immediately below the nonlinear layer  38  there are provided temperature compensation dielectric layers  40  and  42 . Immediately below the layer  42  there is provided a frequency selective layer  44 . 
     The dimensions and relative sizes as shown in FIG. 1 are for illustrative purposes and do not necessarily represent actual dimensions or size relationships. Actual dimensions are primarily a function of the selected operating frequencies. 
     The interior of the housing  12  has a surface  50  which is reflective to the microwave energy present within the amplifier  10 . The region within the housing  12  between the lower surface of the plate  14  and the surface  50  comprises a pump signal cavity  52  (low band) which is tuned to the frequency of the input signal ω 1 . The region within the housing  12  between the lower surface of the plate  14  and the frequency selective layer  44  comprises a harmonic cavity  54  (high band) which is tuned to the frequency of the pump signal ω 3 , which is a harmonic of the input signal ω 1 . In a selective embodiment, the signal ω 3  is a third harmonic of the signal ω 1 , that is, ω 3  has three times the frequency of ω 1 . 
     The amplifier  10  further includes a second group of layers  45 ,  46  and  48 , which are offset by a gap below the layers  38 ,  40 ,  42  and  44 . The layers  45  and  46  are temperature compensation dielectric layers corresponding to the previously described dielectric layers  40  and  42 . The layer  48  is a frequency selective layer that corresponds to the frequency selective layer  44 . However, layer  48  has a different cut-off frequency. The frequency selective layer  48  is transparent to the input signal ω 1 , but is reflective for an intermediate frequency ω 2 , which has a greater frequency than ω 1 , but a lesser frequency than ω 3 . For example, the signal ω 3  can be three times the frequency of signal ω 1  and the signal ω 2  can be twice the frequency of signal ω 1 . Thus, these signals can be harmonics of each other. A preferred relationship is ω 3 =ω 2 +ω 1 . 
     The region between the lower surface of plate  14  and the frequency selective layer  48  comprises a cavity  55 , which is an idler frequency cavity for energy of the signal ω 2 . 
     The circulator  62  can comprise a latching circulator such as Model OP320 sold by Channel Microwave Corporation, 480 Constitution Avenue, Camarillo, Calif. 93012. 
     The nonlinear material layer  38  is preferably a doped superlattice, which comprises a photonic band gap structure. Such structures are described in “Photonic Band-Gap Structures” by E. Yablonovitch in  Journal of the Optical Society of America Bulletin,  Volume 10, No. 2, February 1993, pp. 283-295. As described in the article, the dimensions of the material are a function of the operating frequency. An applicable photonic band gap structure is further described in “Applications of Photonic Band Gap Structures” by Henry O. Everitt in  Optics and Photonics News,  November 1992, pp. 20-23. 
     The temperature compensation dielectric layers  40  and  42  are preferably dielectric layers chosen for their dielectric property behavior over frequency and thickness, so as to achieve a given level of volume fill to achieve temperature compensated device operation. This technique is described in HTS Microwave Cavity with Temperature Independent Frequencies-Mueller, et al. in IEEE Transactions on Applied Superconductivity, Vol. 5, No. 2, June 1995, pp. 1983-1986. 
     The temperature compensation dielectric layers  40 ,  42 ,  45  and  46  may exist separately from, or form part or all of the frequency selective layer  44 . 
     The frequency selective layers  44  and  48  are preferably fabricated as described in “Low-Loss Microwave Cavity Using Layered-Dielectric Materials” by C. J. Maggiore, et al. in  Appl. Phys. Lett.  64(11), Mar. 14, 1994, starting at p. 1451. The arrangement of dielectric materials described in this paper is a superlattice. 
     The amplifier  10  is shown in FIG. 1 with a rectangular configuration, which in a selected embodiment can have a length dimension of approximately one (1) inch and a thickness of approximately 0.25 inch. However, it can have other shapes, such as rectangular or round, with the size primarily depending upon the necessary sizes required for the tuned cavities  52 ,  54  and  55 . 
     The embodiment shown in FIG. 1 uses microwave waveguides but can also utilize other microwave conductors such as microstrip and coaxial lines. 
     U.S. Pat. No. 5,731,752 entitled “Microwave Signal Frequency Multiplier which issued Mar. 24, 1998 is incorporated by reference herein. The structures shown in this patent may be utilized as a part of the present invention. 
     An electrical schematic circuit  60  is shown in FIG. 2 for illustrating the operation of the amplifier  10  shown in FIG.  1 . Elements that are common to FIGS. 1 and 2 carry the same reference numeral. A source  70  indicates a generator for the input signal ω 1 . The source is connected to the circulator  62  via waveguide  60 . The output signal ω 1  from the circulator passes through a resistor  72  which represents the impedance of the waveguide  68  for the output signal ω 1 . The cavities  52 ,  55  and  54  correspond to the similarly numbered cavities shown in FIG. 1. A variable capacitor  74  represents the nonlinear layer  38 . The pump signal ω 3  is generated by a source  80 . 
     The operation of the amplifier  10  as represented in the schematic circuit  60  and as shown in FIG. 1 is as follows. The relatively low amplitude input signal ω 1  is provided through the waveguide  60  to the circulator  62  where it is transferred through the opening  66  in the plate  14  to the interior of the amplifier  10 . The higher energy pump signal ω 3  is input through the waveguide  74  to the interior of the amplifier  10 . A high energy field is built up within the cavity  54  due to the input of energy by the signal ω 3 . The lower energy input signal ω 1  is resonant within the cavity  52 . The lower energy signal ω 1  causes carriers produced by the higher energy signal ω 3  in the nonlinear layer  38  to be transferred along with the energy of the signal at the frequency of ω 1 , thereby enhancing the energy of signal ω 1  within the cavity  52 . Energy is also transferred from the ω 3  cavity  54  to the intermediate cavity  55  and from there into the ω 1  cavity  52 . The result is that the energy resonant within the cavity  52  is increased over that which would be present if the signal ω 3 , the pump signal, were not present. This energy is transferred through the waveguide  64  to the circulator  62  where it is passes out through the waveguide  68  as the enhanced amplitude output signal ω 1 . Thus, the output signal ω 1  in the waveguide  68  is amplified from the input signal ω 1  which is received through the waveguide  60 . 
     This operation is further described in reference to the wave form shown in FIG.  3 . The input signal ω 1  is represented by the waveform  110 . The output, which is the amplified signal ω 1 , is represented by the waveform  112 . The pump signal ω 3  is represented by the waveform  116 . Note that all three signals have steady state amplitudes for this operation. The diode capacitance/voltage function of the amplifier  10  is shown by the curve  114 . The energy of the signal ω 3 , at a higher frequency than that of ω 1 , is utilized to increase the amplitude of the input signal ω 1  to produce the output signal of ω 1 . Thus, the amplifier  13  functions as a parametric amplifier. 
     In applications where one microwave signal is already being generated at a high frequency, such as for radar, and lower frequency microwave energy is needed, the present invention is particularly applicable. 
     Although one embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention.