Prediction of far-field patterns using synthesized steerable spatial filtering functions

An improved version of the integral equation formulation proposed earlier by Biraud (1971, 1976) for predicting the far-field patterns of aperture antennas from measured near-field data is presented. It is shown that the numerical computational work can be significantly reduced by performing the near-field measurements over a large surface so as to realize a band-pass spatial filtering function which is inserted into the integrand. This filtering function, corresponding to the pattern of a synthesized array, can be beam-steered by means of multiplying the near-field measurement values with appropriate sets of coefficients and then summing them up vectorially. The synthesized array may have a semicylindrical or spherical surface as well as a planar one. The solution of the integral equation is based on converting it into a simple matrix equation by expanding the unknown plane wave spectrum functions of the measured antenna into sampling series with unknown coefficients. The sampling series may assume different forms according to the type of the zero-one function of the aperture.<>