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
d
and the number of elements
M
increase. When
d
is greater than 0.2λ, the cumulative distribution curves of an
M
-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
M
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.