MIMO communication; electromagnetic coupling; fading channels; finite difference time-domain analysis
Previous results for correlated block-fading MIMO channels with covariance information indicate guaranteed capacity growth with additional transmit elements and that in rapidly fading channels, vanishing element spacing maximizes capacity. However, because prior analysis neglects antenna electromagnetic coupling, the observations are not necessarily valid for small inter-element spacing. This work applies radiated power considerations to the analysis to demonstrate that additional elements do not always increase capacity and that vanishing element spacing is not optimal. An effective gain metric is introduced that quantifies the performance increase with additional transmitters in the presence of transmit correlation and mutual coupling. Performance simulations using the electromagnetic properties of uniform linear arrays characterized by closed form expressions for Hertzian dipoles and detailed finite-difference time-domain (FDTD) simulations of half-wave dipoles illustrate that capacity gains arc possible when correlation stems from directional bias in the channel but not when it arises due to compact element spacing.
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