Near-field corrections to line-of-sight propagation

This study considers the line-of-sight propagation of electromagnetic waves in a turbulent medium. Interest here centers on the received signal's phase stability. The field equation describing propagation through a region characterized by random dielectric fluctuations is first developed. Solutions of this equation which represent the scattered field are derived with ordinary perturbation theory. These solutions are next used to calculate the rms phase error for an arbitrary path in the troposphere. This approach includes both a three-dimensional and near-field description for the multipath, scattered amplitudes, thereby overcoming the limitations of previous treatments. The phase correlation between signals received on two parallel transmission paths is derived last to illustrate the role of overlapping antenna beams.