Numerical Procedures for Handling Stepped-Radius Wire Junctions

摘要

This report considers the numerical determination of the current and charge induced on stepped-radius wires by electromagnetic sources. A numerical technique is presented which provides an accurate solution for the current and charge on collinear stepped-radius wires. With this technique the detailed behavior of the current and charge in the vicinity of the step change in radius is also determined. A numerical technique employing the thin-wire theory approximations is also presented. This thin-wire approach requires no condition to be enforced on the charge at junctions of wires of dissimilar radius and yields accurate current and charge distributions away from the junction region. The concept of a 'jump condition' for the charge on stepped-radius wires is discussed, and a numerical charge jump condition is computed and compared with the analytical expression of Wu and King. The use of a charge jump condition in other thin-wire theory approaches which require such a condition is discussed. In particular, the accuracy of the Numerical Electromagnetics Code (NEC), which explicitly enforces a charge jump condition at junctions of wires dissimilar radii, is a charge jump condition at junctions of wires of dissimilar radii, is investigated. The effects on numerical and charge distributions of the explicit enforcement of a charge jump condition and suggested limitations of the NEC code with regard to the modeling of stepped-radius wires are discussed. (Author)