Pre-Compliance Specific Absorption Rate (SAR) Evaluation of a Smart Phone Using Near-Field Over the Air (OTA) Measurements and Advanced Post-Processing Link Approach

The need for fast and accurate measurement techniques for electromagnetic exposure from modern communication devices has increased since few years. The exposure metric for frequencies up to 10 GHz is the Specific Absorption Rate (SAR). The Link approach has been studied and validated since few years to evaluate the SAR for passive antennas and some active devices which can be controlled in terms of output power and have no automatic power adjustment mechanism. In this paper, we go a step further and apply the Link approach to measure the SAR for a commercial smart phone, where we have no a priori knowledge or control, over the power control mechanism, and the antenna position inside the phone. The measurements are done with a 10MHz bandwidth LTE signal communication, between a commercial smart phone, and the Radio Communication Tester (RCT) emulating a mobile Base Station. The E-field distribution and SAR values, computed from the Link approach, are compared to results from the same DUT measured with a legacy SAR (single probe with a robot and phantom) measurement system. The results show SAR values, within 2.8% (0.1dB) for 10g SAR, and −7.1% (−0.3dB) for 1g SAR (at 5mm separation between phone and phantom), between the Link and Legacy approach. The SAR values at Omm separation distance are calculated using extrapolation, and the difference is 7.0% (0.3dB) for 10g SAR and −6.2% (0.28dB) for 1g SAR. Based on these results, it is shown that the Link approach is a faster alternative SAR measurement approach, applicable for pre-compliance, during early stage of development, and for post-production scenarios.