On two different formulations of the Coupled Mode Method: Application to 3D rectangular chirowaveguides

This paper develops two different formulations of the Coupled Mode Method (CMM), called EH-indirect and EH-direct formulations, for rectangular waveguides nonhomogeneously loaded with bi-isotropic media. The results of the EH-indirect formulation are compared with the more usual EH-direct formulation, and its range of applicability is established. When the EH-indirect or EH-direct formulations of the CMM are combined with the classical Mode Matching Method (MMM) a hybrid technique is obtained that is capable of solving three-dimensional (3D) discontinuities without restriction in number. The results of the generalized scattering matrix for the two formulations are compared and it is concluded that the indirect formulation gives more accurate results than the direct formulation.