Applying MIMO technology in small wireless devices leads to closely spaced antennas, which results in antenna mutual coupling (MC) and highly correlated signals. In this paper, we investigate the effect of the terminal load impedance of the antennas on the MIMO capacity in the presence of the mutual coupling. We use a new concept of receiving mutual impedances to model the MC effect, which has been shown to have a much better performance than the conventional open-circuit voltage method in different applications of array antennas. Simulation results for a 2×2 MIMO system with half-wavelength dipoles in different scattering distribution scenarios, show that in our proposed method, an optimum value of the terminal load impedance ZL of the antennas can be obtained to maximise the capacity for all scattering distributions, whereas the conventional methods need to different ZL in different scattering scenarios.
