Efficient Methods for Determining the Coupling to Wires in Circular Cavities

The electromagnetic field coupling to a loaded thin wire in a cylindrical/coaxial cavity is investigated. Computationally efficient methods are presented for determining the coupling to a thin wire located near a cavity wall in a system of cascaded and/or overlapping coaxial and circular cylindrical cavity sections, and the accuracy and limitations of these methods are established. The sections are coupled through apertures and conducting elements common to more than one section, which may have different axial and radial dimensions and which may be filled with material having different magnetic and electric properties. The loaded thin wire is close to the outer wall of a cavity section and may represent a cable or, perhaps, a conducting tube. The coupling of the cavity field to the wire is determined from an analysis of a distributed voltage and current source model based on transmission line theory as well as via coupled integral equations techniques. The accuracy of the results obtained from these analyses is supported by experimental data measured on a laboratory model of the cavity-wire structure.

I. Introduction

There is an increased interest in understanding how signals penetrate into a system and propagate to a digital electronics device deep inside the system. Circular cavities are common in these systems since these shapes are easily manufactured and can be handled by humans. How waves penetrate into, propagate along, and couple to wires inside these circular cavities is important to be able to understand the electromagnetic susceptibility of these larger systems. This paper builds upon the coupled integral equation method for determining the fields in a set of cascaded coaxial/cylindrical cavities developed by Young et al. [1] and extended to cavities with overlapping sections by Bopp and Butler [2]. Here, we present two computationally efficient methods for approximating the current on an internal wire, cable, or conducting tube located near the outer cavity wall of a coaxial or cylindrical cavity. One method is based on transmission line theory, and the other one is based on integral equation methods.