Efficient evaluation of specific absorption rate for MIMO terminals

Multi-antenna-enabled terminal devices are required to comply with the standards for limiting human exposure to electric fields. However, when compared to the traditional single-antenna terminals, a comprehensive evaluation of specific absorption rate (SAR) for multi-antenna terminals is impractical. This is because both the power allocation and the phase of the electric fields from different antennas are arbitrary in practical multiple-input-multiple-output (MIMO) operation, hence requiring exhaustive evaluation over all possible cases. In this context, first, the time-averaged simultaneous peak SAR (TASPS) is proposed as an efficient metric to evaluate the exposure when more than one antenna is transmitting simultaneously. Then, it is analytically derived that TASPS will be below a given exposure limit, as long as the stand-alone peak SAR for each antenna is smaller than that limit. Thus, SAR evaluation is greatly simplified since only the stand-alone SAR needs to be measured. Several examples of dual-antenna mobile handsets are shown to illustrate and validate the analytical result.