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A theoretical discussion of the possibilities for the design of a parametric amplifier using a pump frequency lower than the signal frequency (but higher than one half the signal frequency) is given. In particular, a detailed mechanism for the operation of a ferrite amplifier with such properties is described. The amplifieroperation is similar to that used by Bloom and Chang for a diode amplifier with cubic nonlinearity. Hogan,Jepsen, and Vartanian have proposed a ferrite device to serve the same purpose as the present amplifier;however, their scheme is quite different, and a detailed comparison is given in this paper. The main feature of the present amplifier is a doubling of the pump frequency to obtain an effective pump frequency which is larger than the signal frequency. The whole amplifier requires four resonances:the pump frequency, twice the pump frequency, the signal frequency, and twice pump minus signal (idle). The most efficient assignment of the modes uses cavity resonances for the signal and pump, and then uses either cavity or ferrite resonances for the other frequencies. Since the pump doubling is a result of nonlinear mixing, the efficiency of doubling will be greater for larger pump fields. This is limited in practice by the onset of saturation in the ferrite. For pump fields close to saturation the required pump field is calculated to be five to ten times larger than that required to produce the same gain in an ordinary three resonance amplifier.
Peter Gottlieb (Sun,) studied this question.
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