Antenna array beamformers suffer from performance deterioration in the presence of mutual coupling (MC) between array sensors. In this paper, we present a theoretical analysis in terms of the output signal-to-interference-plus-noise ratio (SINR) for the performance of antenna array beamformers under MC effects. Based on the model of a distortion matrix to encapsulate the MC effects, a closed-form expression for the SINR is derived that is shown to accurately predict the SINR obtained in simulations. This theoretical formula is valid for any distortion matrix estimated from collected measurement data. The SINR formulas provide insights into the influence of the MC effects on the performances of the linearly constrained minimum variance (LCMV) beamformer and the eigenspace-based (ESB) beamformer. It is shown that the ESB beamformer outperforms the LCMV beamformer under MC effects. Moreover, we derive the formulas for computing the eigenvalues of signal correlation matrix under MC effects. Simulation results are presented for confirming the validity of the theoretical results.
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