Optimization of Linear Multielement Antennas for Selection Combining by Means of a Butler Matrix in Different MIMO Environments

An optimized linear multielement antenna (MEA) is presented for selection combining schemes that improves the selection diversity gain and selection diversity capacity in medium and low multipath environments, with respect to the performance achieved with a simple uniform linear array (ULA) using omnidirectional antennas, while it performs equally as well as a ULA in highly scattered environments. An analytical investigation based on the analysis of the correlation coefficients, together with simulations and extensive measurements, have been carried out for different fading multiple-input multiple-output environments ranging from line of sight (LOS) to non-LOS. Two MEAs are compared: a simple ULA with omnidirectional antennas and a MEA combining a ULA and a Butler matrix. The measurement results show that the nature of the proposed MEA is such that it is adaptive to any propagation scenario by simultaneously taking advantage of beamforming gain and signal diversity gain.