Microwave propagation over mountain-diffraction paths

An experimental study was undertaken to obtain a more complete picture of wide-band transmission via microwave propagation over mountain-diffraction paths. Such paths are characterized by obstacles of irregular shape, and pathlength very large compared to wavelength. Swept-frequency transmission was used to provide a record of signal-level variations with time and frequency on two different paths. Other observations included polarization dependence, spatial variation, and direct comparison with repeater-relayed signals. The two paths were selected on the basis of obstacle shape; in one case a conical mountain peak, in the other a cylindrically-topped ridge. While the gross features of the data were in agreement with conventional theory, significant detailed departures were noted on the mountain peak path. It was concluded that, in general, the effects of a nonuniform transverse obstacle profile must be taken into account in microwave diffraction. A comparison of data from the two paths supported this conclusion. The "repeater model" of diffraction was also examined and found to be of dubious value for the paths in question.