Effects on Correlation Between Two Mobile Radio Base-Station Antennas

TLDR

The study investigates the correlation between signals received by two mobile radio base‑station antennas to determine spacing requirements for space diversity. The authors measured UHF signal fading between two horn antennas at various spacings and orientations, then repeated the experiment with local scatterers removed. Experimental results agree with the derived analytical expression and show that the critical spacing along the line connecting the antennas is about 70 wavelengths, dropping to 30 wavelengths when the incoming wave is 10° off‑axis, and that local scatterers reduce correlation, establishing an upper limit on antenna spacing within the achievable range.

Abstract

The correlation between signals received by two mobile radio base-station antennas is investigated to determine spacing requirements for space diversity. Measurements of the fading of UHF signals received by two base-station horn antennas oriented at different angles with respect to the incoming mobile radio signal were made for different antenna spacings. The experimental results are compared with an analytical expression derived in this paper; they agree fairly well. A further experiment was made after removing the possible local scatterers surrounding the base station. Comparing these two experimental results, we find that the following are true. 1) Propagation in the direction of a line connecting the two base-station antennas is the critical case and requires a large separation of 70 wavelengths. As soon as the incoming wave is 10° away from the inline axis, the spacing requirement drops to 30 wavelengths. 2) Local scatterers at the base station tend to decrease the correlation between signals received at the two antennas. We conclude that an upper limit to the spacing of antennas used for diversity can be obtained and that it is within the achievable range.