Mutual Coupling Effect on Maximum-Ratio Diversity Combiners and Application to Mobile Radio

The mutual coupling effects on an
M
-branch maximumratio combiner with correlated signal fading in general are considered. The results in the mobile radio case show that the average power delivered to the receiver becomes less as the antenna spacing of an antenna array decreases (i.e., the mutual coupling increases) with either an optimum load network or an optimum resistive load network connected to the antenna array at the front end of the receiver. However, there is not much effect on the power as long as the antenna spacing is equal to or greater than a certain value dependent on the number of the branches
M
. For
M \leq 4
, the required antenna spacing is equal or greater than 0.2λ. The value for
M > 4
increases gradually as
M
increases. It can be obtained following the same technique. The mutual coupling effect on the cumulative distribution of the signal from an
M
branch mobile diversity array is also small. Hence for an in-line array with
M \leq 4
, the antenna spacing of 0.2λ can still provide most of the usual diversity advantage.