Channel Capacity of MIMO Systems with Closely Spaced Terminated Antennas

We investigate the antenna impedance mismatching effect on thermal noise power, in addition to the mutual coupling effect on signal and noise. We provide an analysis of the channel capacity of multiple antennas terminated by three most common matching decoupling networks. We confirm that the achievable information rate of the multiple antennas terminated by self- and characteristic impedance matching network is below the information throughput that could be achieved by the multiple antennas terminated by the multi-port conjugate match. Yet the actual information rate degradation due to the imperfect matching network is lower than the case when the noise coupling is omitted from the analysis. The result indicates on the potential of the transit output power savings. Therefore, we suggest that the design of the matching decoupling networks should be based on the maximum signal-to-noise ratio criteria rather than maximum achievable signal power as both signal and noise powers are affected by the mutual coupling effect and consequently by antenna mismatching impedance.