Microwave bistability in a magnetostatic wave interferometer with external feedback

Microwave bistability has been obtained for the first time in a magnetostatic wave (MSW) interferometer with external magnetic field feedback. The interferometer contained a magnetostatic surface wave transmission line with a 7.5-/spl mu/m thick epitaxial film of yttrium iron garnet magnetized with an external static magnetic field of 1048 Oe, a variable attenuator in a parallel reference channel, and external feedback in the form of an additional static field derived from the line output. Bistable and multistable output power versus input power responses are derived from the frequency dependence of the interferometer transmission and the MSW wave number dependence on the static magnetic field. Typical bistable and multistable output versus input power hysteresis loops were obtained under constant frequency operation in the range 4.9 to 5.2 GHz, and for input powers from -30 to +10 dBm. The bistable response depends on the frequency of the microwave signal, the attenuation in the reference channel, and the gain of the feedback loop. An analysis based on linear MSW theory agreed with experiment. Applications of MSW microwave bistability include power limiter devices and basic microwave logic elements.