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.

I. Introduction

Measurements for the antenna system efficiency in a MIMO configuration is an essential procedure to characterize the overall system performance. This includes the radiation efficiency of the antenna, which is defined as the ratio between the radiated power to the accepted power by the port [1]. Recently, wireless communication technologies exploit MIMO antennas as transmitting and receiving diversity components to enhance the capabilities of systems [2], [3] in terms of communications channel capacity and bit rate [4]. The increase of using MIMO antennas in several commercial devices, that mostly depend on communication with high bit rates, makes it essential to have a reliable, handy, and cheap MIMO antennas’ efficiency measurement tool for development and evaluation purposes.