Application of the fundamental matrix method for two-point boundary-value problems to mode coupling in a parallel-plate waveguide having multiperiodic wall corrugations

The authors solve the numerical two-point boundary-value problem arising from the multimode stopband interaction of TM waves in a parallel-plate waveguide having nonuniform wall corrugations along the direction of propagation, which coincides with the z-axis of a Cartesian coordinate system. The fundamental matrix method developed by O. Asfar and A. Hussein (see J. Numer. Math. Eng., vol.28, no.5, p.1205-16 (1989)) for stiff systems of linear ordinary differential equations is used. The method has been applied to two filter design examples for a waveguide cutoff at 5 GHz: a filter section with constant coefficients and a filter with slow sinusoidal taper. The filter response is given in terms of the power reflection coefficient and is improved by tapering