GB850707A - Improvements in or relating to travelling wave amplifiers - Google Patents

Abstract

850,707. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. Oct. 6, 1958 [Dot. 30, 1957], No. 31802/58. Addition to 850,036. Class.40 (9). The pumping wave, signalling wave and idler wave of a travelling wave parametric amplifier are transmitted over a common channel. The terms "impedance" and ' " reactance " are used in. the broad sense described by Schelkunoff. Lumped impedance elements, Fig. 1.-A pumping wave fp and a signal wave f1 are applied through de-coupling resistors 4, 3 to an iterative network in which either the inductors L or the capacitors C or both are non-linear. The amplified signal f1 is accepted by filter 6 and is applied to a load 5. The filter rejects the pumping wave fp and an idler wave f2, where #1 = #p - #2. For amplification the pumping wave must be of sufficient amplitude to mask the pumping effects of the signal and idler waves. It is desirable also that the phase constants of the waves should satisfy the relations #p = #1 + #2 and where f represents frequency. When both L and C are non-linear, variations in L must be in phase opposition to variations in C. Distributed impedance.-The network may be replaced by two flat strips of metal 11, 12, Fig. 2, spaced apart by a slab of ferro-electric material 13. A battery 8 biases, the ferro-electric material so that there is no reversal of field by the waves. In another arrangement, Figs. 3, 3A, two metal plates 15, 16 are spaced apart by a manganese ferrite 17 of high resistivity or by yttrium - iron garnet. These materials are capable of gyromagnetic resonance and have a dielectric constant of the order of 10. The line is placed between magnetic poles 21, 22, Fig. 3A, in a direction parallel to the pole faces and perpendicular to the field. The strips are turned, as shown, at 45 degrees to the magnetic field H so as to satisfy three necessary conditions : (1) the magnetic vector of #1 (or #2) has a component parallel to the steady magnetic field H; (2) the magnetic vector of f2 (or f1) has a component perpendicular to the steady magnetic field H; (3) the magnetic vector of the pumping wave fp has a component perpendicular to H. The high-frequency magnetic fields hl, h2 of the signal and idler waves and,the field of the pumping wave can be resolved as shown into components parallel to one perpendicular to the field H. In Fig. 5, the pumping and signal waves are transmitted over a helical conductor 30.wound around a core 31 of gyromagnetically resonant material. The core is disposed at 45 degrees to the magnetic field H between two poles 21, 22. The signal wave #1 may be transmitted along the core - used as a dielectric wave-guide. Coaxial line. Fig. 4.-The pumping wave fp and the signal wave fl may be transmitted through a coaxial line comprising inner and outer conductors 25, 26. The waves are coupled by means of-one or more rods 28 of gyromagnetic material interposed between the inner and outer conductors. The coaxial line is placed in a magnetic field with the magnetic field at 45 degrees to the plane defined by the central conductor and the gyromagnetic rod. Waveguides.-The pumping and signal waves may be transmitted along a wave-guide 35, Fig. 7, of rectangular section. A ferrite rod 36 couples the travelling waves. A strip of ordinary dielectric material 37 may be used to equalize the speeds of the pumping, signal and idler waves. The guide is disposed in a magnetic field H, as shown in Fig. 8A. As the ferrite rod has a dielectric constant of the order of 10, it may be used as a dielectric waveguide 36, Fig. 8, for the signal wave, the pumping wave being transmitted along the rectangular guide. The cut-off of the guide 35 must be below the pumping frequency fp but may be above the signal frequency. An impedance transformation from high-current and low-- voltage to low-current and high-voltage or vice versa may be secured by using a tapered transmission line. Specification 839,596 also is referred to.