Hybrid finite element solution of a quadrupole gyromagnetic waveguide

Quadrupole bias fields are applied to ferrite-loaded waveguides in the implementation of nonreciprocal microwave quarter-wave plates. Specifying the tensor values and demagnetising effects for the ferrite in this type of bias field is difficult owing to the nonuniformity of the field and the existence of nonsaturated regions. A two-stage finite element solver is described here which may be used to evaluate the propagation characteristics of this type of geometry. Propagation constants are presented here for a magnetised square ferrite waveguide. The differential phase shift as a function of applied field is found to be linear and a backward wave exists over a narrow frequency band for one of the dominant modes