Electromagnetic coupling between wires inside a rectangular cavity using multiple-mode-analogous-transmission-line circuit theory

This paper examines the coupling between two arbitrarily positioned wire segments inside a rectangular enclosure. The enclosure is treated as a superposition of analogous transmission lines which have been short circuited at two positions on the propagation axis. Each analogous transmission line is associated with a particular waveguide mode in the cavity. Previous work has used this analogy to predict the coupling between two monopoles inside a small box using the dominant TE/sub 10/ mode. This paper considers the general case of high-frequency coupling between two wire monopoles in a large rectangular cavity, where several higher order modes are active. By taking into account higher order modes, and the mutual coupling between the modes, a simple equivalent circuit is presented which can give a prediction for the coupling between the monopoles. Experimental results for various monopole pair positions are shown, which indicate the success of the multimode theory. The technique requires far less computer resources than traditional methods for solving such a problem (e.g., MoM, TLM or FDTD), with solution times of less than a second on an average PC. In addition, considerable insight into the coupling process can be gained by including or excluding particular waveguide modes. This is not possible with numerical methods.