Wave-Front Observations at 35 Ghz on a Line-of-Sight, Radio-Wave Propagation Path

摘要

Preliminary analyses of experimental results are described. The experiment consists of line-of-sight propagation of a 35 GHz radio wave over a 28-Km path. The propagated wave is received on an eight-element antenna array in which amplitude and phase are measured and recorded from each element separately and (nearly) instantaneously. Fluctuations imposed on the wave by the atmosphere are the subject of study. Detailed data taken on two particular occasions are discussed. Time-lagged correlations of amplitude fluctuations show motion of disturbances past the array, as well as indicate the scale length of the fluctuations and the time required for atmospheric internal motions to de-correlate the amplitude pattern. Similar correlations of phase-differences (or apparent wavefront tilts) across the array show the phase disturbances to be moving with velocities sometimes equal to those of the amplitude disturbances and sometimes different in an intriguing way. The apparent pattern velocities determined by correlation have been compared with measured spectral widths of the fluctuations. Correlation of wavefront tilt with amplitude fluctuations proves interesting, the correlation being zero at zero time lag and the sign for positive and negative lags depending upon the direction of motion of the fluctuations past the array. The amplitude and phase information has been used to compute antenna patterns, and the resulting motions of the antenna 'lobe' have been measured. They show displacements in azimuthal angle-of-arrival as large as 30 arc-seconds. (Author)