Measurements of Phase-Front Distortion on an Elevated Line-of-Sight Path

An experimental study has been made of phase-front distortion in microwave signals sent over a slanted path. This distortion is important in systems involving phase measurements between a ground station and a moving upper terminal. To insure path stability, the upper terminal was simulated by a series of mountaintop antenna arrays. Phasefront distortion is analyzed in terms of time variations in radio range on a single path and in terms of first and second range differences between pairs of paths. The cross correslations of pairs of range and range difference records are discussed, and the strong dependence of correlation on fluctuation frequency is emphasized. Mountaintop terrain effects on the spatial homogeneity of the phase front are found to be insignificant. Some of the phase-front statistics are found to be weakly dependent on time of day and on wind velocity at the lower terminal.