Mode Coupling in TEM-Cells due to Variations in the Geometry using Generalized Telegraphist’s Equations

This paper deals with the propagation of electromagnetic waves in coaxial TEM-Cells. The general theory of electromagnetic wave propagation in TEM-Cells is of high interest because of its practical use as a measurement environment. A semi-analytical method is used for computing the electromagnetic fields within the TEM-Cell. The so-called Generalized Telegraphist’s Equations will be developed for the TEM-Cell. This approach is particularly suitable for analyzing the electromagnetic fields because it not only calculates the overall field inside the TEM-Cell, but it also shows the mode coupling due to the variation of the geometry. This method, also known as cross-section method or coupled-mode theory, is applied to reduce the Maxwell equations to an infinite set of ordinary differential equations for the basis amplitudes of the eigenvectors of the electric and magnetic fields of a TEM-waveguide. As a numerical example, a tapered concentric coaxial TEM-Cell will be considered.