Aperture-to-medium coupling on line-of-sight paths: Fresnel scattering

An electromagnetic signal propagated through a medium of randomly varying dielectric exhibits random-phase fluctuations. The phase of the total signal is the average of all rays which strike the reflector and is therefore smoothed by a receiver-reflector combination of finite aperture. This paper presents a theoretical analysis and numerical results for this phase-smoothing for small phase perturbations. The receiver is assumed to be a circular parabolic reflector with a collecting feed at the focus. The propagation is described by Fresnel scattering and the one dimensional ray theoretical expressions employed. Closed form results are obtained for three separate space correlation models of the random dielectric medium. These results are valid so long as the scattering parameter
L\lambda l_{0}^{-2}
is small.