COMPUTATION OF CUTOFF WAVE-NUMBERS FOR PARTIALLY FILLED WAVE-GUIDES OF ARBITRARY CROSS-SECTION USING SURFACE INTEGRAL FORMULATIONS AND THE METHOD OF MOMENTS

A procedure for determining the cutoff wavenumbers of partially dielec tric filled waveguides of arbitrary cross section is presented. A nume rical approach based on surface integral formulations and the method o f moments is used to obtain a matrix equation. Muller's method is then applied to find the wavenumbers that make the matrix determinant vani sh. These are the cutoff wavenumbers. On the conducting walls of the w aveguide, perfect electric conductor, perfect magnetic conductor, and imperfect conductor surfaces are considered. The transverse electric a nd magnetic cases are treated separately. The impedance boundary condi tion and the symmetry of the waveguide cross section are used to reduc e the matrix size in the method of moments. Spurious modes have not be en observed using this method. To validate the accuracy of this method , results for circular, partially filled rectangular, and two walled c orrugated rectangular waveguides are compared to analytical results. E xamples such as T-septate rectangular, coaxial, and dielectric-loaded double-ridged waveguide are also considered. Accurate prediction on th e cutoff wavenumbers is achieved.