Spatial correlation in uniform circular arrays based on a spherical-waves model for mutual coupling

A general framework based on spherical waves is presented for arbitrary oriented antenna elements in a uniform circular array configuration. The technique fully describes all electromagnetic effects in the array by a set of spherical-wave coefficients. This set is limited by the overall electric size of the array. It is demonstrated that the signal correlation between the antenna elements can be calculated directly from these spherical-wave coefficients for certain statistical distributions of the directions of arrival of the incoming signals. The effects of antenna tilt on the signal correlation are investigated. It is shown that because of mutual coupling and pattern non-uniformity, signal correlation can both increase and decrease compared to the case of an ideal array consisting of isotropic and uncoupled antenna elements. Moreover, simulation results show a significant reduction of the mean channel capacity, compared to CmaxCmax, for uncorrelated antenna signals and omnidirectional antenna elements.