Simplified technique for evaluating the radiation integrals

A simplified numerical method is described for computing the radiation integral of a reflector antenna which is associated with either the aperture field method (AFM) or the induced current method (ICM). The method involves linear approximation of the phase function and absorption of the approximation error into amplitude function. Then the integrand is rewritten as a slowly varying function multiplied by the phase exponential. The slowly varying function is expanded in terms of a polynomial for the radial direction and trigonometric functions for the circumferential direction. Expansion coefficients are determined by matching at points on the aperture. The matching points are chosen in a manner similar to that of a two-dimensional numerical integration scheme.