The Effect of Mutual Coupling on Directivity and SNR in Super-Directive Antenna Arrays

Electrically small antenna arrays are of increasing importance as more and more wireless devices are equipped with multiple antennas. This paper studies the effect of mutual coupling on two aspects of small arrays: super-directivity and SNR gain. It is shown that if one uses the standard array signal processing model (assuming isotropic antennas and a direction independent mutual coupling matrix) then super-directivity is invariant to the effect of coupling. However, coupling does affect the sensitivity of the array to thermal noise when super-directive beamforming is employed.