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A ferromagnetic parametric amplifier requiring fractional watts of pump power has been developed and investigated experimentally. The amplifier employs magnetostatic modes as resonances which are parametrically pumped by a longitudinal rf magnetic field. A theoretical discussion of the characteristics of longitudinal parametric pumping on the magnetostatic modes is presented including selection rules for determining which pairs of modes can be pumped and an expression for the threshold pump field required for pumping the modes to oscillation. A relation for the gain-bandwidth product of the amplifier is derived, and it is shown how the coupling to the modes must be adjusted to maximize the gain-bandwidth. A model of the amplifier has been built which utilizes X-band pump power and amplifies at C-band frequencies. The signal circuit is a coaxial line with a loop connected from the center conductor around a sphere of yttrium iron garnet providing coupling to the magnetostatic modes. Results are presented of measurements at two different pump frequencies. In addition, several mechanisms are suggested as possible sources of noise in this amplifier.
R. T. Denton (Wed,) studied this question.