Capacity of multiple antenna systems in free space and above perfect ground

Multiple input-multiple output (MIMO) systems are a promising technique for wireless applications that require high data rates. In this letter, we theoretically study their capacity potential for propagation in free-space and over a ground surface. We investigate how this depends on the array geometry and the electric field polarization. Moreover, we validate our theoretical predictions with measurements above a nearly perfectly flat surface. The experiment shows good agreement with the theory for a large range of distances and deviates from it when secondary effects (roughness etc.) become more significant.