Stochastic Near-Field Theory and Techniques for Wideband Electromagnetic Emitters at In-Band and Out-Of - Frequencies.

Theoretical and numerical analyses were performed to study the application of near-field theory and techniques to characterize the radiation and coupling characteristics of wideband, in-band and out-of-band pulsed or cw radiating systems. Specifically, stochastic theory and equations were developed for characterizing the radiation patterns of wideband cs or pulsed antennas over both in-band and out-of-band frequency intervals from measured data collected via near-field measurement techniques. The results are applicable to either phased array or reflector antennas. Three analytical techniques for analyzing the in-band and out -of-band coupling between pairs of cosited antennas were studied. The three techniques are (1) the Plane Wave Spectrum (PWS), (2) the Spherical Wave Spectrum (SWS), and (3) Geometrical Theory of Diffraction (GTD). The existing theory and equations that are applicable to selected common waveguide components under normal in-band operation were extended to describe wideband out-of-band responses. Also, the theory and equations were formulated for computing the higher-order mode coefficients at the aperture of a waveguide radiating element from a knowledge of the measured far-field electric field of the radiating element when surrounded by a large conducting "ground" plane. Equations for describing the effects of near-field obstacles located in the antennas' forward half -plane on the performance of a wideband cw or pulsed antenna were derived via the Plane Wave Spectrum (PWS) analysis technique. The resultant statistical average pattern versus frequency is expressed explicitly in terms of the antenna system mode excitation statistical parameters.