Ray mode coupling analysis of EM wave scattering by a partially filled trough

In this paper, a high frequency asymptotic ray technique has been applied to analyze electromagnetic plane wave scattering by a partially filled trough. In the formulation, the modal description has been retained inside the waveguide region. Coupling between the waveguide modes and coupling between modes and rays at the aperture are treated systematically by using matrix form. Though multiple diffraction effects are included here, we also need to consider the radiation contribution from evanescent modes. This can be a considerable amount when the width of the aperture gets very narrow, and only very few modes become propagating ones in the parallel plane waveguide region.<>