Effect of Antenna Mutual Coupling on Degree of Freedom of MIMO Systems

The effective channel matrix for a multiple-input multiple-output (MIMO) system is formulated and investigated when mutual coupling among the antenna elements is taken into consideration. It is found that, in general, the antenna mutual coupling decreases the degree of freedom (DoF) of MIMO channels when the inter-element distance is less than several wavelengths. But the DoF reduction is not monotonia with the decreasing of the inter-element distance.