Cross Correlation in a Space-Diversity System on a Military Vehicle.

Mobile reception in built-up areas is disturbed by interference-fading effects due to multiple incident waves caused from reflecting and scattering objects in the vicinity. The fading can be reduced with the help of space-diversity systems, i.e. with more than one antenna on the car. The fade-reduction factor or the diversity gain of such a system strongly depends on the cross correlation of the antenna-output voltages. The related correlation factor is a function of frequency, is influenced by the car's surface, and depends on the mounting locations of the antennas. If a space-diversity system shall be established, proper antenna locations on the car in mind have to be determined. This report records the results of determining the cross correlation between antennas for various antenna-mounting configurations for a US Army 1/4-ton truck, M151 A2. The antenna receiving patterns are measured for the various configurations. These signal strength measurements are converted to correlation factors of signal power by assuming a Rayleigh distribution of the multipath signal strengths. The Rayleigh distribution has been shown to accurately characterize multipath reception in the 30-80 MHz band in built-up areas. In this manner, the requirement for time-consuming test drives was eliminated, and a more thorough investigation of the cross correlation phenomena was made possible for the same resources. (Author)