The impedance matching problem in the presence of signal and noise coupling in compact MIMO arrays is addressed. By maximizing an upper bound of the ergodic capacity for an N×N MIMO system with signal and noise coupling at the receiver in high signal-to-noise ratio (SNR) scheme, a set of equations is formulated to find the optimal matching circuit. A closed-form result for the optimum matching circuit is given. For two-element arrays, we show numerically that significant performance improvement can be achieved by introducing the optimal matching.
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