Low-SAR MIMO Antenna Array Design Using Characteristic Modes for 5G Mobile Phones

A low specific absorption rate (SAR) multiple-input and multiple-output (MIMO) antenna array is designed for 5G mobile phones based on the theory of characteristic modes (TCMs). First, a geometrically symmetric dipole antenna is analyzed using TCM. The modal currents with symmetrical and reverse distributions are selected and excited to obtain the low-SAR antenna element. Then the antenna element is further optimized, and eight antenna elements constitute an MIMO array. The −6 dB impedance bandwidth of the proposed MIMO array is from 3.4 to 3.6 GHz. The isolations between different antenna elements are higher than 16 dB. Their total efficiencies range from 48% to 67%. Its envelope correlation coefficient (ECC) is lower than 0.08. The 1 g spatial-average head SAR and 10 g spatial-average body SAR of the proposed antenna are simulated and measured.