The Effect of Mutual Coupling on the Nulling Performance of Adaptive Antennas

The effect of mutual coupling on the performance of adaptive antennas has been a topic of considerable interest for the last three decades. The general conclusion of the work reported in the open literature is that mutual coupling degrades the performance of adaptive antennas. We have carried out an in-depth study of the effects of mutual coupling on the performance of adaptive antennas. Our studies show that this conclusion is not entirely correct. Yes, one does need the in-situ array manifold to obtain the fixed response in the desired signal direction. Otherwise, adaptive weights can also suppress the desired signal. Note that for adaptive antennas based on minimizing the mean squared error between the array output and a locally generated reference signal, this is not an issue. However, mutual coupling between antenna elements hardly affects the nulling performance of adaptive antennas. In fact, in a given size aperture, as the number of antenna elements is increased, one obtains better nulling performance, irrespective of the increased mutual coupling between antenna elements. Also, as expected, for strong wideband interfering signals, one should carry out space-time adaptive processing (STAP).