Diffraction at open end of waveguide

Abstract

Thus far only single diffraction of a penumbra field at a wedge has been discussed, tacitly assuming that at a subsequent stage of diffraction the fields incident on the edges will be again ray-optical. However, there are problems with successive diffractions where in each diffraction order the incident field is penumbra. In the circumstances, the scattered field is of the same order in ka (a is characteristic dimension) as the incident field and so one has to sum all successively arising diffraction waves. The simplest example of this variety is diffraction at the open end of a waveguide. It serves as a model for many related problems: diffraction at the open end of a waveguide with nonsymmetrical flanges or with impedance boundary conditions, a wide slot in a waveguide, an oblique-cut waveguide, and a waveguiding cross (intersection of two waveguides). Also related to this geometry are the three-dimensional problems of the open end of a circular pipe with conical flange, which arises in circular waveguide-horn junction analysis, and the allied problem of plane wave incidence on a sawtooth-profiled surface (Wood echelettes). Some of these problems are discussed in this chapter.