MIMO Antennas Efficiency Measurement Using Wheeler Caps

A simple and reliable measurement-based procedure is proposed to predict the radiation efficiency of multiple-input-multiple-output (MIMO) antennas using Wheeler caps. Based on only measuring the S-parameters of the MIMO antenna system in free-space and inside a shielded Wheeler cap, the method approximately predicts the radiation efficiency of each uncoupled MIMO antenna port. The method makes use of the recently developed contactless Wheeler cap concept and the improved quality factor method to facilitate the processing of the results. The procedure is verified by comparing full-wave results with prediction through measurements.