Experimental Comparison of Angle and Space Diversity for Line-of-Sight Microwave Links

In line-of-sight (LOS) links which use space or frequency diversity to combat multipath fading, the fading in each diversity branch is uncorrelated provided the antenna spacing or frequency separation is sufficiently large. Therefore, the availability or outage probability of space and frequency diversity systems is closely described by independent (uncorrelated) Rayleigh fading statistics. In the case of angle diversity, uncorrelated Rayleigh fading does not describe the performance of the angle diversity system. In fact, the fading on the two branches is positively correlated when the fades are shallow and negatively correlated when the fades are deep; i.e., if a deep fade occurs in one branch there is a high probability that the signal in the other diversity branch will not fade. In this paper we discuss briefly the theory of angle diversity and present the results of a short experimental program to compare the performance of angle diversity and space diversity on a fading LOS microwave link.