Effect of Mutual Coupling on a Mobile-Radio Maximum Ratio Diversity Combiner With a Large Number of Branches

The effect of mutual coupling on a space diversity combined signal from an optimum resistive load network lessens when the antenna spacing and the number of elements increase. When is greater than 0.2λ, the cumulative distribution curves of an -branch signal with mutual effects included show only a small difference compared to an array with no coupling, and are close to the cumulative distribution curve of an array with independent branches. For the average SNR of an array with 100 branches obtained from an optimum resistive load network to be within -3 dB of the SNR from independent branches the required antenna spacing is at least 0.25λ, for an in-line array and 0.5λ, for a planar array. Since a planar array is much smaller than an in-line array for equal performance, the planar array is a more desirable configuration.