Practice and Evaluation for Ceiling-Mounted MIMO Indoor Base Stations With Antenna Optimization and SAR Touch Compliance

Antenna design for indoor base stations (BSs) needs to consider various requirements to maximize the performance of the entire system in complicated environments. In this article, antenna design and performance evaluation are conducted from a holistic perspective using a modified multiplexing efficiency. This metric considers power constraints due to electromagnetic field exposure compliance and indoor channel environments for multiple-input multiple-output (MIMO) antenna systems. In the case study, using the reference monopole antenna, the accepted power needs to be reduced from 0.5 to 0.28 W to achieve specific absorption rate (SAR) touch compliance, resulting in a reduction in the modified multiplexing efficiency. The improved monopole antenna design can meet SAR touch compliance with an accepted power of 0.5 W by altering the electric current distribution on the monopole and ground plane. The system performance evaluated using the modified multiplexing efficiency is therefore improved by approximately 2.4 dB in the indoor environment for an indoor BS with four antennas. This holistic antenna design and evaluation process provides a valuable basis for comparing and optimizing MIMO antenna systems while considering SAR touch compliance and deployment scenarios for indoor BSs.