The Number of Fades in Space-Diversity Reception

Experimental and theoretical results are presented which show that deep fades due to multipath propagation on line-of-sight microwave links are greatly reduced in number when two vertically separated receiving antennas are used and the stronger of the two received signals is selected as the diversity signal. The experimental results are based on 6 GHz propagation data obtained for a 72-day period on a 28.5 mile path in Ohio, with a 27.5 foot vertical separation of the receiving antennas. The theoretical results are obtained by treating the received signals as correlated Rayleigh distributed random variables. Theoretically predicted variations with fade depth agree with experimental observations. Combination of the theoretical results with experimentally determined parameters provides results which can be used, for example, to calculate the reduction in the number of fades as a function of the vertical separation of the receiving antennas, wavelength, path length, fade depth, and the gain difference (if any) of the receiving antennas.