Patent GB-850036-A (GB)
Title: Improvements in or relating to travelling wave amplifiers
IPC: H03F7/02
Filed: 1958-06-03
Abstract: 850,036. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. June 3, 1958 [June 6, 1957], No. 17710/58. Class 40 (9). A travelling-wave parametric amplifier comprises separate channels for a signal wave of frequency #1 and an idler wave of frequency f2. The two channels are coupled by a variable parameter such as reactance controlled by a pumping wave of frequency fp in a third channel where fp = f1 + f2. There is no need for any harmonic relation between #1, #2 and #p but if fp = 2#1 a single channel may carry both signal and idler frequencies. The channels and the couplings may be built up of either lumped or distributed impedances. For optimum results, it is desirable that the phase constants of the waves should satisfy the relations where P 1  # 2 , # p  are phase constants and w is angular velocity. The terms " impedance " and " reactance " are used in the broad sense described by Schelkunoff. Low frequencies 60 c/s. to 10<SP>6</SP> c/s., lumped impedances.-Signal, idler and pumping channels 1, 2, 3, Fig. 1, comprise iterative networks of impedances L1, L2, L3 and C1, C2, C3. Channels 1 and 2 are linked by saturable inductors 8 controlled by the pumping wave in channel 3 which in effect produces a reactance wave in the line of inductors. The channels 1 and 2 are terminated with their characteristic impedances 6 and 7 to avoid reflections. An amplified version of the signal frequency f1 may be derived from the terminal load 6 at frequency f1 or from the terminal load 7 at frequency f2. The output of the pumping channel is fed back to the input through buffer amplifiers 13, 11. A third buffer amplifier 10 is included in the pumping input circuit. Alternatively, the line may be terminated so as to reflect the pumping wave and thereby to form standing waves. In Fig. 2 (not shown) the variable inductors of Fig. 1 are replaced by variable capacitors or reactance valves. High frequencies, distributed impedance.-In an amplifier, Figs. 3, 4, using a pumping frequency of about 9 X 10<SP>9</SP> c/s., the pumping channel is a circular waveguide 23. The signal and idler frequencies #1, #2 are guided on pairs of conductors 21a, 21b and 22a, 22b. The channels are coupled by a filling 25 of manganese ferrite, of yttrium iron garnet or of a rare earth iron garnet. The guides are placed between the poles N, S of an electromagnet which is adjusted so that a gyromagnetic resonance frequency of the filling material 25 falls in the region of the pumping frequency. The arrangement satisfies the three necessary conditions for amplification set out in Specification 839,596. From Fig. 4 it can be seen that (1) the magnetic vector of one (fl) of the two lower frequency waves has a component parallel to the magnetic field H, (2) the magnetic vector of the other (2f) of the two lower frequency waves has a component perpendicular to H. To satisfy the third condition (3) the magnetic vector loops of the pumping wave (not shown) are in planes parallel to the plane of conductors 22a, 22b and have components perpendicular to H. As shown, the three channels for the signal idler and pumping waves are terminated by their characteristic impedances 6, 7, 24. The ends of the circular waveguide may be closed by conductive sheets 26, Fig. 5, so as to form a standing pumping wave. The terminating impedance 7 of the idler line is embedded in the material 25 and the pumping wave may be introduced at any electric node by means of a coaxial line 27 and a probe terminating the inner conductor. In another arrangement, Fig. 6, the signal and idler waves travel along a rectangular waveguide 31 in different nodes, the magnetic vector loops of one wave lying parallel to the horizontal face of the guide, as shown, and the loops of the other wave parallel to the vertical face. The pumping wave is fed to a second rectangular guide 32. The guides are coupled by a ferrite rod 33 filling a longitudinal slot in the common walls of the two guides. Specification 652,155 is referred to.