A study of the roughness propagation effects in waveguides with the mode matching technique combined with the method of moments

In this paper, we study the electromagnetic wave propagation in a parallel plate waveguide with rough surface walls, using a mode matching technique in combination with the method of moments (MoM). In the formulation, a line source in the smooth section of the waveguide excites a summation of modal fields. For each waveguide modal excitation, the modal response fields in the rough surface section of the waveguide are obtained by the solution of the governing surface integral equations through MoM. The total field distribution in the rough surface waveguide is a linear combination of the modal response fields. The coefficients are obtained by enforcing the continuity of tangential electric and magnetic fields at the junctions between smooth and rough surface waveguide sections. Results are illustrated for a variety of roughness spectra based on the parametric generalized power spectral density. The results are compared with the previously developed small perturbation method of second order (SPM2) results for the plane wave and waveguide models. With the numerical validation, the SPM2 waveguide model is proved to be able to capture the waveguide thickness effect especially for very rough surface profiles.