Scattering at rectangular waveguide to quasi-optical cavity junction

A formally exact solution is given for the problem of scattering at the junction of rectangular waveguide to quasi-optical cavity by mode matching method. The normal TE and TM modes are utilized to expand fields in rectangular waveguide. Gaussian beam modes are employed to express fields in quasi-optical cavity. By applying the boundary condition of the transverse electric and magnetic fields at the interface between the two regions, a matrix equation for the amplitude of each mode is established. Generalized scattering matrix [S] can be readily deduced from the matrix equation. Numerical results of the S-parameter for the dominant TE₁₀ mode in rectangular waveguide are calculated. The results are graphically compared with those obtained by a hybrid technique of finite element method and Gaussian mode expansion method.