The complete surface current distribution in a normal-mode helical antenna using a Galerkin solution with orthogonal sinusoidal basis functions

When wires are closely parallel, the surface current distribution on them becomes nonuniform. This effect has been investigated previously, but the earlier studies were restricted to simple geometries and neglected the possibility of a circumferential component in the surface current: it is intuitively obvious that such a component must be present when there is significant displacement current flow in the inter-wire capacitance. With approximated methods, surface resistive losses and reactive effects that may be augmented by the non-uniform surface current will not be correctly predicted. This problem is particularly significant for resonant coiled electrically-small antennas, such as the normal-mode helical antenna (NMHA), in which the surface current distribution has a critical effect on the efficiency, Q-factor and resonant frequency. A new moment-method (MoM) formulation was thus developed which overcame this problem; however, this used simple basis functions, posing a risk of error, and hence a more elegant version has been developed, using piecewise-sinusoidal basis functions with a Galerkin solution.