Analysis of a feeding structure for TEM wave excitation in an oversized rectangular waveguide

A post-wall waveguide-fed parallel-plate slot array has a feed waveguide to excite a plane TEM wave in an oversized rectangular waveguide. It is a cascade of junctions, each of which consists of a coupling window with reflection and grating-lobe canceling posts, in front of and behind it, respectively. In the conventional design of the feeding structure, uniform illumination of all the windows coupling to an infinitely large parallel plate is discussed; a unit junction is defined which assumes two periodic boundary walls in the parallel plate waveguide and the periodicity of the field in the parallel-plate waveguide in the transverse direction. This model is valid only for a very large aperture. Furthermore, the parallel plate waveguide is shorted at both sides to compose an oversized rectangular waveguide. Field distribution near the narrow walls is expected to be affected by the sidewalls. In this paper, we analyze the full structure of the feeding structure in an oversized rectangular waveguide by the method of moments. We calculate the power dividing characteristics at each junction and the field distribution in the oversized rectangular waveguide.