Mutual coupling effects in multi-user massive MIMO base stations

We analyze the effects of mutual coupling and spatial correlation on the performance of multi-user MIMO systems having a large number of antenna elements at the base station (`large-scale' MIMO or `massive' MIMO). We show that these effects set a practical limit on the maximum number of antennas that can be packed into any given physical base station size, above which no further spectral efficiency gain is achieved. Different antenna elements such as dipoles, patches and dual-polarized patches are considered.