Trade-Off Analysis of Mutual Coupling Effect on MIMO Antenna Multiplexing Efficiency in Three-Dimensional Space

We analyzed the relation between two opposite effects of mutual coupling (MC), correlation reduction and gain loss, on the MIMO antenna performance in three-dimensional (3D) space. In the antenna level, those MC effects can be represented in terms of two main MIMO antenna parameters: the antenna correlation and radiation efficiency. The main contribution of this paper is the derivation of MC-related effects only on the antenna parameters, which then can be plugged into multiplexing efficiency, a realistic antenna-level MIMO performance metric, to evaluate the trade-off between two opposite MC effects. Uniform linear arrays with and without polarization diversity are used to analyze the MC effects, and to clarify the ambiguities of their contributions on the MIMO performance. The impacts of azimuth and elevation angular spreads to the MC and MIMO antenna performance are also investigated. Results show that the MC, contrary to common intuition, has a positive contribution to the MIMO performance relative to when MC is not considered in the system, especially at small antenna spacing. It implies that the correlation reduction dominates the gain loss from the MC effects. So, we can infer that the MC actually is not the reason for performance degradation in small spacing antenna arrays.