The Cutoff Region of a Rectangular Waveguide with Losses, Its Properties and Uses

Physical waveguides have walls with finite conductivity and enclose diclectric regions that have finite losses. The usual high conductivity metals and low-loss dielectrics have little effect on wave propagation at frequencies well above and below the cutoff frequency region.* These metallic and dielectric losses, however, have a pronounced effect in a small frequency region that includes the nominal cutoff frequency for a particular mode as determined for a lossless waveguide of the same geometry.1 The purpose of this paper is the theoretical and experimental investigation of the properties of a physical waveguide operated at frequencies in this latter region. The scope of this investigation is limited to a rectangular waveguide operated in the 8.2 to 12.4 GHz band of frequency (X band). The dominant mode of the lossless waveguide, the T E I 0 mode, serves as the initial model for an analysis of a similar mode configuration when losses are present. The analysis is divided into two parts: first, the waveguide is assumed to have two narrow walls with conductivity * F r o m the disertation submitted to the faculty of the Polytechnic Institute of Brooklyn in partial fulfillment of the requirements for the degree of Doctor of Philosophy (electrophysics), 196S. t For a lossless waveguide, the cut frequency is a singular point for the propagation constant of a waveguide mode. 2221