Patent GB-839802-A (GB)
IPC: H03F7/02
Filed: 1958-05-13
Abstract: 839,802. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. May 13, 1958 [May 20, 1957; Nov. 7, 1957], No. 15306/58. Addition to 839,596. Class 40 (9). A modification of the parametric amplifier described in the parent Specification comprises a block 10 formed with a resonant cavity 12 and a resonant strip line comprising a strip conductor 17 and a cavity 16 disposed at right-angles to the major axis of the cavity 12. Discs (or cubes) 25, 26 of gyromagnetic material such as manganese ferrite or yttrium-iron garnet are secured to the middle of the conductor 17 and serve as a support therefor. The material is preferably a single crystal material. A pumping frequency #p is fed through an iris 14 to the cavity 12. A signal frequency #1 is fed to the cavity 16 and an amplified signal of the same frequency is extracted from the cavity by waveguides 19, 23 and capacitative probes 21, 22. The gyromagnetic material is biased by a magnetic field H directed parallel to the block and at 45 degrees to the axes of the cavities 12, 16. The cavities are cast or milled in the block 10 and are covered by a plate 11. Fig. 2 shows how the conditions necessary for amplification or oscillation are satisfied. The signal frequency magnetic field h#1 has a component perpendicular to H. The second signal frequency magnetic field, h#1 again, has a component parallel to H and the pumping frequency magnetic field hfp has a component perpendicular to H. The gyromagnetic material provides a non-linear coupling between the oscillations fp, #1 in the two cavities and parametric amplification takes place when #p =#1+#1=2#1. If the pumping energy supplied at frequency fp exceeds a threshold value, the system is unstable and oscillations are generated. If the energy supplied is below the threshold value, the system is stable and serves as an amplifier. If the signal includes a frequency band based on #1 the output in guide 23 includes two sidebands, one of which may be removed by filter 27. Modifications.-In one modification, Fig. 3, the cavity 55 resonant of the pumping frequency is arranged parallel to the magnetic field H and at 45 degrees to the axis of conductor 17. The field H is thus perpendicular to the entire transverse field of #p in the region of the discs 25, 26. In another modification, Fig. 4, a signal frequency #1 is supplied to cavity 16 and an amplified signal may be derived either from cavity 16 at #1 or from cavity 12 at #2 through waveguides 23, 37. The strip lines comprising conductors 17 and 35 are resonant at frequencies #1,#2. The pumping frequency #p=#1+#2 is fed as before to cavity 12 and is not affected by the conductor 35. The gyromagnetic discs 25, 26 provide the only coupling between the anodes. The discs 25, 26 of Fig. 1 may be replaced by discs 45, 46, Fig. 5, arranged as shown. These discs are each cut from a single crystal of magnesium ferrite, manganese ferrite or yttrium-iron garnet. The discs are resonant at sharplydefined magnetostatic resonance frequencies at which they show low absorption and high Q in contrast to the high absorption and low Q of resonance due to precession of electron spins. The pumping frequency fp is chosen so that #p=#1+#2 when #1 is the signal frequency and #2 is a magnetostatic resonance frequency.