On Cross Correlation in Antenna Arrays With Applications to Spatial Diversity and MIMO Systems

We develop a general approach to cross correlation in antenna systems suitable for applications to spatial diversity and MIMO systems. The far-field correlation is expressed in terms of the currents on the antennas. The basic strategy proposed here is to perform the overall evaluation of cross correlation by means of superposition integrals involving contributions emerging from all possible mutual correlations between the point sources on the antenna currents where interactions are mediated by a new cross-correlation Green´s function. The method is verified and demonstrated in several numerical examples and a design methodology aiming at maximizing the diversity gain is outlined and illustrated. It is also shown that arbitrary antenna arrays can be reduced to suitable models involving only infinitesimal dipoles, in effect enabling us to compute the total diversity gain using the cross-correlation Green´s function. The formulation provided here gives the electromagnetic aspect of spatial diversity an articulated form proper for design and development of practical communication links using multiple antenna systems.