Multiple edge interaction effect to plane wave scattering by a wide and thick slit

High frequency ray method has been applied to formulate E-polarized plane wave scattering by a wide and thick slit. Slit aperture region is considered as a waveguide which connects the upper and lower half spaces, and excitations of the waveguide modes are given by edge diffraction at the open end. Multiple edge diffraction effect as well as modal bouncing effect are also considered to improve the accuracy of the scattering field.