Ferrite-loaded waveguides-a perturbation theory approach

We have developed a perturbation theory for ferrite-loaded waveguides. The perturbation operator is chosen as the deviation of the relative permeability matrix from unity. The method allows a systematic calculation of the propagation constant as well as the perturbed modes to any desired order. It can be used for any direction of the bias field and also for inhomogeneous bias fields as long as the translation invariance along the waveguide is kept. We apply our method to ferrite-loaded waveguides with a bias field in the propagation direction. For the completely filled case, first order expressions for the propagation constant are obtained and the coupling behaviour of TE, TM and TEM modes is discussed. Furthermore we study the scattering of TEM modes in partially filled waveguides and obtain the S-matrix for the ferrite coupled line in the first order.