A ferromagnetic microwave amplifer with increased signal bandwidth

Previous work in ferromagnetic microwave amplification has followed a two-fold course of reducing the necessary pump power by 1) reducing the resonant absorption linewidth and 2) improving the filling factor of magnetic material to the resonant system. These developments have led to the Denton-type amplifier employing a parallel-pumped single crystal sphere of yttrium iron garnet operating in the magnetostatic mode where the pump power is, typically, 1/2 watt. However, the resultant narrow linewidth (or high Q of the resonant absorption) restricts the signal bandwidth to the order of 100 kc/s. This is a major limitation in most applications. This paper describes the multiple pumping process used to remove this limitation of the Denton amplifier. The resulting amplifier has a 2-Mc/s or greater signal bandwidth with the associated increase in gain-bandwidth product while total pump power remains less than one watt. The theory of operation is extended to cover the improved operational stability to temperature and pump power variations. A C-band (5.8 Gc/s) dielectrically loaded version of this amplifier using an X-band pump is described and performance details given.