Tunable resonators

Abstract

In a magnetically-tunable resonator, a wave-guiding structure comprising an electromagnetic frequency filter, or component of such a filter, is placed in sufficient proximity with a magnetic structure so as to be gyromagnetically coupled therewith. The resonator is supportable of two fundamental normal modes of propagation which, in the absence of magnetic interaction are even and odd with respect to the resonator center plane of symmetry. Each normal mode possesses a spectrum of resonance frequencies. When the magnetic structure is magnetized, the formerly even and odd modes become mixed due to gyromagnetic interaction, and the resulting wave fields become elliptically polarized. With appropriate design such that the identities of the modes are preserved under conditions of resonance, this in turn results in a nonreciprocal reinforcement action in the resonator, which leads to the desired shift in resonance frequency in at least one of the two normal modes. The device is especially attractive to application in miniaturized planar microwave devices, for example MMICs, in conferring small size and weight, simplicity of structure, low power required for tuning, capability of fixed, continuous or digitally-stepped frequencies, and low-loss high-Q performance; applicable with superconducting or conventional metallic conductors.