| NOTAS: | "An algorithm is presented for calculating near-zone and Fresnel-region fields in front of microwave antennas from discrete numerical values of the radiated plane-wave spectrum (complex far-field pattern). This is, the near fields are calculated by numerically integrating the plane-wave spectrum representation of the field. The crux of the analysis consists of handling a numerical instability which arises from integrating discrete data. A criterion is developed for limiting the integration domain in order to exclude highly oscillatory regions of the integrand. In turn, this leads to restricting the applicable output range over which the field can be computed. With the numerical instability problem thus resolved, fast Fourier transform techniques are used to assure efficient numerical integration over a large (but restricted) output range. The results are conveniently presented as relative power-density contours in planes formed by the longitudinal coordinate axis and one transverse coordinate axis. The algorithm is capable of extremely high accuracy, which is demonstrated by comparing predicted and measured near fields for two distinct antennas, along with a comparison predicted and measured near fields for two distinct antennas, along with a comparison against an exact theoretical model. In the case of circularly symmetric excitation models for electrically large antenna apertures, the predicted relative near-zone power density contour plots turn out to be a function of just the aperture distribution. Nomographs for obtaining absolute near-zone power densities are presented for new typical aperture distribution functions." |
