Iterative finite element solution for cut-off frequencies of inhomogeneous ferrite waveguides

The frequency dependence of the tensor entries in gyrotropic media results in a non-linear eigenvalue problem for the solution of resonant structures. An iterative scalar finite element method is presented here to calculate the modal resonant frequencies for planar inhomogeneous structures. For these calculations, the gyrotropic medium is modelled using material characteristics taken from the hysteresis curve and a specified applied magnetic bias field. The technique is verified by comparing the calculated cut-off frequencies with the exact solution for a ferrite rod in a circular waveguide. The cut-off plane for a triply ridged waveguide with a ferrite rod is also treated.