Equivalent Circuit for Coupling Through an Annular Slot in a Thick Conducting Screen

The electromagnetic coupling through a small hole in a screen is of interest to investigators in many areas. The thickness of the screen usually causes the reduction of the transmission except when a TEM mode exists. In such a case the transmission coefficient is a periodic function of the thickness and exhibits a resonant behavior at certain thicknesses. This paper presents the analysis for an annular slot in a thick screen and a rigorously derived equivalent circuit for the problem. function for the slot region is constructed using the eigen modes of a coaxial waveguide. Because of the rotational symmetry of the geometry, both types of operators can be decomposed into a sequence of Fourier modes (with respect to the azimuth angle). A sequence of simultaneous equations for the Fourier coefficients of the unknown magnetic currents are the result. The most important of them are the integral equations of the lowest order (no ^-dependence) since the TEM mode is of prime concern.