Perturbation theory approach to the ferrite coupled stripline

Perturbation theory is applied to analyze the ferrite coupled stripline (FCL) with longitudinal magnetization. Up to first order, the fields and propagation constants of the modes are obtained, neglecting the coupling to higher TE and TM modes. Based on this result, the scattering matrix of a FCL structure with a given finite length is calculated. Simple relations which connect the nonreciprocal behavior with the geometrical design parameters and the ferrite material properties are found. The perturbation results are in good agreement with simulation data and thus provide a basis for further design of nonreciprocal devices based on the FCL structure.