On Fast Estimation of SAR for Metallic Rim-based MIMO Handsets

Use of multiple-input-multiple-output (MIMO) antennas in a mobile handset helps to achieve an increased capacity and enhanced spectrum efficiency. Although, specific absorption rate (SAR) is one of the most important and widely used metrics for the characterisation of suitability, safety and compliance of commercial mobile handsets, its estimation for MIMO-enabled handsets is a complex and time consuming process. For the MIMO configurations, the SAR is the vector sum of $E$ fields of individual antenna elements. The phase and amplitude of these $E$ fields are dependent on MIMO precoding. Hence, SAR estimation for MIMO configurations becomes a lengthy and tedious analysis that makes it complex and rather impractical in real measurement scenarios. In this paper, a $2\times 2$ MIMO configuration of the metallic rim antenna is analyzed to study the dependency of phase offset on SAR. The antenna elements are placed on the shorter edge of the metallic rim, resonating at 2.1 GHz. It is estimated that the maximum value of SAR is maintained at 0°, while the handset is used in talking position. This knowledge of phase offset reliance on SAR can help in reducing the overall time for SAR estimation as SAR needs not to be calculated for other phase offsets.