Impact of matching network on the capacity of compact MIMO systems

MIMO is an undisputed breakthrough in advanced wireless technology, as it offers potentially linear increase in information-theoretic capacity with the number of antennas. However, the implementation of MIMO in compact terminals is a relatively uncharted topic, due to challenging problems with high antenna correlation and mismatch loss, both of which greatly reduces the expected MIMO gains. In this paper, we investigate the remedial impact of matching networks on the capacity degradation in such systems with respect to both uniform 2D angular power spectrum and measured wideband outdoor-toindoor channels. We find that the optimum narrowband multiport-matching network can perform poorly in the wideband case. For a modest 2.3% fractional bandwidth, the narrowband and wideband capacities (per unit bandwidth) can differ by as much as 60%. The multipath richness of the propagation scenario is also shown to have an important effect on the benefits that can be derived from more sophisticated matching networks which take into account mutual coupling in their designs.