Self-Decoupling, Shared-Aperture, Eight-Antenna MIMO Array With MIMO-SAR Reduction

This study investigates the multiple-input multiple-output (MIMO)-specific absorption rate (SAR) reduction for a high-isolation MIMO antenna for the application to fifth-generation (5G) communication. A theoretical analysis that links the electric fields (
$E$
-fields) of the MIMO antenna with MIMO-SAR is proposed. The mode cancellation method (MCM) is applied to decouple the shared-aperture MIMO antenna and reduce the design complexity of MIMO-SAR reduction based on theoretical guidance. The collaborative reduction of MIMO-SAR and the mutual coupling of the MIMO antenna are achieved for the first time. To achieve MIMO-SAR reduction, the cancellation of the total current equalization (TCE) generated by the predicted total current mode was verified through a theoretical analysis. As a result, an impressive reduction of 82% in MIMO-SAR and an isolation of 20 dB of the MIMO antenna were achieved with a distance of only
$0.047~\lambda $
between the two ports in antenna pair C. An eight-antenna MIMO array was manufactured to validate the simulation, for which the measured −6 dB impedance bandwidth ranges between 3.4–3.6 GHz, and the isolation is better than 16.7 dB. The measured efficiency is higher than 55%, and the envelop correlation coefficient (ECC) is less than 0.1. The measured eight-port MIMO-SAR is less than 0.85 W/Kg, which is significantly lower than the standard of international commission on non-ionizing radiation protection (ICNIRP).