Parametric amplifiers

A new class of microwave amplifiers has recently been studied in which the active element is a reactor whose value is made to vary at the frequency of a local oscillator usually known as the pump. With suitable circuits, amplification at the frequency of an input signal may be obtained. Alternatively the amplified output signal may be shifted in frequency to a value which is simply related to the frequencies of the input signal and the pump respectively. The active element may consist of an electron stream coupled to a suitable electrode structure, a back-biased junction diode or a ferrite contained in a suitable resonator. In each case the resulting amplifier may be expected to have a very low noise factor and this expectation is confirmed by the results so far obtained.