Surface Current Distribution on Closely Parallel Wires within Antennas

An investigation of the surface current distribution over closely spaced parallel wires acting as components of antennas is reported. A moment-method formulation was developed using two geometrically-orthogonal basis functions to represent the total non-uniform surface current distribution over wire surfaces. Extended basis functions were used to reliably treat the discontinuity of the current at the free ends. A surface kernel was used over all of the antenna structure. The surface current distribution was computed for different antenna geometries such as dipoles, loops and helices. For helices, the currents were investigated for different pitch distances and numbers of turns. It was found that the axially- directed component of the current distribution around the surface of the wire was highly non-uniform and that there was also a significant circumferential (transverse) current flow due to inter-turn capacitance. The impedance characteristic showed good agreement with the predictions of a standard filamentary-current code, in the case of applied uniform excitation along the local axis of the wire. However, the power loss computations produce significantly different results, due to the neglecting of non-uniform surface current concentrations in the standard models.