Simplified treatment of wire-to-plate junctions with magnetic-current frill excitation

A structure consisting of a flat metal plate and a wire joined to the plate and driven at the plate by a magnetic-current frill (approximating the coaxial-line excitation) occurs frequently. The electromagnetic analysis of such a structure poses considerable problems, the main one being due to discontinuous surface-charge density (i.e. to discontinuous surface-current derivative) on the plate near the junction. This has been solved by introducing either different types of so-called attachment mode or additional partitioning of the plate. Both approaches, however, complicate the solution significantly. The authors show that, using a simple theorem, the frill excitation can be transferred to the wire, thus obtaining a model that is much easier to analyse. The theorem is exact for infinite ground plane, but numerical results indicate that it can be approximately applied to plates of finite size, even for wires close to the plate edge. This procedure is particularly useful for relatively thick wires, of length/diameter ratio less than about fifty, where the delta-function generator approximation may not be appropriate.