Abstract:
A Q-switched parametric cavity microwave amplifier has input and output ports for receiving an input signal and producing a switched amplified output signal. A pump signal, preferably at a harmonic of the input signal, is received through a pump signal port and provided to a pump signal cavity within a housing. The pump signal interacts with a non-linear medium to produce carriers. A frequency selective layer reflects the pump signal but permits the input signal to pass therethrough. The input signal interacts with the carriers produced in the non-linear medium to enhance the signal present within the resonant cavity for the input signal. This transfers energy from the pump signal to the lower frequency input signal. A Q-switch is positioned in series with the output waveguide to cause energy to be stored within the input signal cavity. When the Q-switch is opened, a pulse is produced representing an amplified version of the input signal.

Description:
BACKGROUND OF THE INVENTION 
     In certain applications, it is difficult to obtain required microwave energy signals because of restrictions in energy sources, weight and the available volume for such equipment. Such limitations are frequently present in applications involving microwave equipment used in missiles, airplanes, and satellites. In general, it is more difficult to produce microwave signals as the frequency of the required signal increases. One method for producing a high frequency signal is to use a multiplier device such as shown in U.S. Pat. No. 5,731,752 entitled “Microwave Signal Frequency Multiplier.” Certain microwave signals are continuous and others are switched, which are typically used for producing pulses. 
     There exists a need for a switched, microwave amplifier which can store energy from an available microwave source and selectively release this energy as pulses when required. 
     SUMMARY OF THE INVENTION 
     A selected embodiment of the present invention is a switched microwave amplifier which includes a housing having an interior cavity. An input port is connected to the housing for providing an input signal to the interior cavity of the housing. An output port is connected to the housing for conveying an output signal from the amplifier. A pump signal port is connected to the housing for coupling a pump signal to the interior cavity of the housing. The interior cavity comprises a first cavity that is resonant with the input signal and the output signal. A non-linear medium is positioned within the first cavity for producing carriers therein in response to the pump signal. A frequency selective barrier within the interior cavity substantially reflects the pump signal and substantially transmits 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 first cavity as a result of interaction of the input signal and the liberated carriers. The output signal is at the frequency of the input signal and has a greater amplitude than the input signal. A two-state switch is coupled in series with the output port wherein the switch has a first state for blocking transfer of stored energy from the first cavity and has a second state to permit release of the stored energy from the first cavity through the output port. 
    
    
     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 Q-switched frequency multiplier in accordance with the present invention, 
     FIG. 2 is a schematic diagram of the multiplier shown in FIG. 1, 
     FIG. 3 is a chart illustrating the signal production of the multiplier shown in FIG. 1, and 
     FIGS. 4A and 4B are waveforms which contrast operations with and without the Q-switch of the present invention. 
    
    
     DETAILED DESCRIPTION 
     A switched parametric amplifier  10  in accordance with the present invention is illustrated in FIG.  1 . The amplifier  10  receives an input signal ω 1 . Within the amplifier  10 , the input signal is amplified to produce an output signal ω 1 . The amplifier  10  includes a Q-switch which causes a build-up of energy from the input signal and a pump signal and selectively releases this energy as a switched, amplified output signal. 
     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 . The housing  12  and plate  14  are preferably made of brass, aluminum, or plated dielectric material. 
     The input signal ω 1  is provided to the amplifier  10  through an input wave guide  28  which is secured to the top plate  14 . The input microwave signal ω 1  is transferred through an opening  30  in the plate  14  to the interior of the housing  12 . The amplifier  10  includes an output wave guide  32  which is mounted on the plate  14  and receives microwave signal energy via an opening  39  in the plate  14 . A Q-switch  36  is mounted within the wave guide  32  and functions to either block or pass the output signal ω 1 . The Q-switch  36  receives a control signal via a line  37  to selectively turn the switch  36  on and off. 
     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 non-linear layer  38 . Immediately below the non-linear 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 illustrated in FIG. 1 are for illustrative purposes and are not necessarily in proportion to that which is shown. Actual dimensions are primarily a function of the signal frequencies which are used. 
     The interior of the housing  12  has a surface  50  which is reflective to the microwave energy present within the amplifier  10 . 
     A pump signal ω 3  is transmitted through a waveguide  31  and an opening  33  to the interior of 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  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 signal cavity  54  which is tuned to the frequency of the pump signal ω 3 . 
     The region in the amplifier  10  between the lower surface of plate  14  and the frequency selective layer  94  comprises an idler cavity  55  which is tuned to the frequency of the signal ω 2 . 
     The Q-switch  36  can be fabricated as any one of the following: 
     (A) PIN diode switch, as described in Application Notes for Bulk Window™ waveguide switch elements, pages  3 — 3  through  3 - 8 , M/A Com Semiconductor Products Operation, Burlington, Mass. 01803. 
     (B) Micro-Electro-Mechanical Switches (MEMS) as described in U.S. Pat. No. 5,880,921 by Tham, et al. which issued Mar. 9, 1999 and is entitled “Monolithically Integrated Switched Capacitor Bank Using Micro Electro Mechanical System (MEMS) Technology.” A further description of this type of switch is given in an article “DARPA Sows Seeds of a Telecom Revolution,” EE Times, Monday, Aug. 4, 1997, starting on page 1. 
     (C) Laser diode switched photoconductive materials/window as described in U.S. Pat. No. 5,796,314 to Tantawi, et al. entitled “Active High-Power RF Switch And Pulse Compression System.” 
     (D) Bulk avalanche semiconductor switch (BASS) as described in U.S. Pat. No. 4,782,222 to Ragle, et al. entitled “Bulk Avalanche Semiconductor Switch Using Partial Light Penetration And Inducing Field Compression.” 
     (E) A latching circulator such as Model OP320 sold by Channel Microwave Corporation, 480 Constitution Avenue, Camarillo, Calif. 93012. 
     The non-linear material  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, Feb. 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 , Nov. 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 by Mueller, et al. in IEEE Transactions on Applied Superconductivity, Vol. 5, No. 2, June 1995, pp. 1983-1986. 
     The temperature compensation dielectric layers may exist separately from, or form part or all of the frequency selective layer  44 . 
     The frequency selective layer  44  is preferably implemented 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 material described in this paper is a superlattice. 
     The amplifier  10  is shown in FIG. 1 with a square configuration which in a selected embodiment can have side dimensions 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 amplifier  10  includes a second group of layers  90 ,  92 , and  94  which are offset by a gap below the layers  38 ,  40 ,  42 , and  44 . The layers  90  and  92  are temperature compensation dielectric layers corresponding to the previously described dielectric layers  40  and  42 . The layer  94  is a frequency selective layer that corresponds to frequency selective layer  44 . However, layer  94  has a different cut-off frequency. The frequency selective layer  94  is transparent to the input signal ω 1 , but is reflective for an intermediate frequency signal ω 2 , which is at 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 signal ω 2  can be twice the frequency of signal ω 1 . 
     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. 
     In operation, the switch  36  is placed in a first state to block the transfer of energy from the amplifier  10  while input energy in the form of signal ω 3  is received. This energy is transferred to the cavity  54 , but as the pump signal ω 3  passes through the non-linear layer  38 , carriers are generated which interact with and become a part of the input signal ω 1 . The energy of the pump signal ω 3  is transferred to the cavity  52  for the signal ω 1 . The frequency selective layer  44  is transparent to the input signal ω 1 , the lower microwave frequency, but is reflective to the harmonic microwave pump signal ω 3  which is at a substantially higher microwave frequency. Thus, the energy of the signal at the frequency of ω 3  is transferred to the cavity  52 , and the energy level of signal ω 1  is increased by the power derived from the pump signal ω 3 . 
     When the Q-switch  36  is switched to its second state and becomes transparent to the signal ω 1 , the energy within the cavity  52  is transferred through the opening  39 , the switch  36  and out through the wave guide  32  as signal ω 1 . In blocking the output signal by use of the switch  36 , energy from the pump signal ω 3  can be stored as energy in cavity  52  to produce a high energy pulse of the input signal ω 1  upon opening the switch  36 . The output signal ω 1  is a pulsed signal which is an amplified signal of the input signal ω 1 . 
     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 numerals. A source  62  indicates a generator for the input signal ω 1 . A variable capacitor  68  represents the nonlinear layer  38 . The cavities  52 ,  54  and  55  shown in FIG. 2 correspond to the similarly numbered cavities shown in FIG.  10 . The switch  36  shown in FIG. 2 corresponds to the Q-switch  36  shown in FIG.  1 . 
     In operation, the pump signal ω 3  is provided through waveguide  31  into cavity  54  where the energy of this signal interacts with the nonlinear layer  38  to produce liberated carriers in this layer. The input signal ω 1  is provided through waveguide  28  to the cavity  52 . When the signal ω 1  encounters the free carriers in the layer  38 , many of these carriers are swept along with the signal ω 1  thereby transferring energy for this signal to cavity  52 . The signal ω 3  is preferably a harmonic of signal ω 1 . The energy of the pump signal ω 3  is transferred to the cavity ω 1  to enhance the amplitude of the A signal. 
     The Q-switch  36  blocks the release of energy from the cavity  52  thereby  10  causing energy to be built up in this cavity during the time that the switch is closed. When the state of the switch  36  is changed to conductive for signal ω 1 , the energy from cavity  52  is released as an output signal through the output waveguide  32 . The output signal ω 1  is at the same frequency as the input signal ω 1 . 
     The frequency selective layer  94  defines the intermediate cavity  55  which stores energy of an intermediate signal ω 2 . The signal ω 2  and cavity  55  function as a transfer stage for moving energy from the pump cavity  54  to the cavity  52  for signal ω 1 . 
     The relationship of the signals used in the amplifier  10  are shown in FIG.  3 . Waveform  110  represents the input signal ω 1 . The waveform  112  represents the output signal of ω 1 . The pump signal ω 3  is represented by the waveform  114 . The transfer function of the amplifier  10  as primarily provided by the nonlinear layer  38  is shown by curve  116 . 
     FIGS. 4A and 4B represent a comparison of operation of the amplifier with and without the use of the Q-switch  36 . FIG. 4A represents the above described operation. Waveform  82  represents the pump signal ω 3 , such as a pulsed radar signal. Waveform  84  represents a pulse of the output signal ω 1 . The switch is turned off at the start of the waveform  82  and is opened at the start of waveform  84 . In contrast, as shown in FIG. 4B, waveform  86  represents the output signal ω 1  without use of the switch  36 . The waveform  84  shows a higher peak energy than that present for waveform  86 . Thus, the switch  36  functions to store energy from the pump signal during the time between the start of the pulses  82  and  84 , and releases this energy as a pulse of signal ω 1  as shown by waveform  84 . 
     Although only 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 embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention.