Performance of directive multi-element antennas versus multi-beam arrays in MIMO communication systems

In an isotropic rich scattering environment, the shape of the patterns of the elements has long been considered as irrelevant to their Multiple-Input and Multiple-Output (MIMO) performances. In the current communication it is cleared that the directivities of the embedded elements, which are immediate outcomes of their patterns, contribute to the diversity gains as well as capacity of the system. Indeed, the number of scatterers plays a significant role in this respect. It is demonstrated that unless the number of scatterers is high enough, the diversity gain and capacity do not reach their final limits, even though the spatial correlation and radiation efficiencies reside on their ideally best levels. A brief study of the matter is presented in this paper and the simulation results are verified by measurements in reverberation chamber.