Modelling a standard broadcast directional array with the numerical electromagnetics code

摘要

The numerical electromagnetics code (NEC) is a general-purpose wire-antenna-analysis computer program capable of modelling both a standard-broadcast directional array (DA) and a scatterer such as a power line. The starting point for such a study is a NEC model of the directional array itself. The DA's admittance matrix could be used to choose voltage excitations for the NEC model such that NEC's tower-base currents agree in magnitude and phase with those of the array's design. However, this choice of excitation is unsatisfactory because NEC's azimuth pattern differs from the theoretical azimuth pattern which is computed using sinusoidal current distributions on the DA towers. The difference is accounted for by the phase of the tower currents: in the NEC model the phase varies with height above the ground on each tower, but in the sinusoidal current approximation, the phase of the tower current is constant. In the present study the NEC model of the DA is regarded as being out of adjustment, and the objective is to adjust the excitation of the NEC model such that its azimuth pattern matches the array's theoretical pattern.