GB996346A - Diode parametric amplifier - Google Patents

Abstract

996,346. Parametric amplifiers. MULLARD Ltd. Jan. 14, 1964, No. 1620/64. Heading H3B. A parametric amplifier has a waveguide section A, tunable to resonance at the pump frequency and with a cut-off frequency higher than the idler frequency, a voltage-dependent capacitor diode D within the waveguide and having one terminal connected to the waveguide wall and the other terminal against the free end of the central conductor of a coaxial line E, and a reactive isolating section U in series with the diode and the coaxial line which inhibits propagation of pump and idler frequencies along the coaxial line, while forming with the diode a circuit tuned to resonance at the signal frequency. In Fig. 1 the isolator is a choke the series reactance of which can be varied by varying the diameter of central portion T. A portion W of coaxial line E is formed as an impedance transformer with two steps, each one quarter wavelength long. Alternatively portion W may be smoothly tapered (Fig. 2, not shown). In Fig. 5 the isolator is a low-pass filter Y, Z. Portion Y adjacent diode D is made longer than the other sections to provide adequate series inductance. Where a tapered impedance transformer H is provided (Fig. 9) the isolator may be a section Y of the central conductor which is less than a quarter wavelength long at the idler frequency. Its diameter determines its series inductance. In a modification (Fig. 10) the isolator and diode are interchanged. A similar modification to Fig. 5 is referred to. The isolator may be capacitive at the signal frequency, e.g. section U in Fig. 1 may be made three-quarters of a wavelength long at the idler frequency so as to be capacitive for signal frequencies between one third and two-thirds of the idler frequency. The idler frequency is set up in a parallel resonant circuit comprising the diode, its holder, and any stray capacitances. The diode may be biased. Specification 984,254 is referred to.