Some observations of antenna-beam distortion in trans-horizon propagation

3000-mc signals from a rotating narrow-beam transmitting antenna have been observed at distances from 92 to 177 miles. The manner in which the received power builds up and falls off as the transmitting beam sweeps past the receiver shows a variety of shapes instead of merely reflecting the transmitting-antenna patterns as would be expected on a line-of-sight path. From a series of these received-power patterns, mean received power as a function of transmitting-antenna azimuth is obtained and, from this, an angular scattering function is derived. This angular scattering function, which is a characteristic of the path only, is used to predict the optimum antenna size for this path. These observations are also used to predict the improvement provided by a diversity system employing two identical receiving beams separated in azimuth only.