Low-SAR Four-Antenna MIMO Array for 5G Mobile Phones Based on the Theory of Characteristic Modes of Composite PEC-Lossy Dielectric Structures

A low-specific absorption rate (SAR) four-antenna multiple-input–multiple-output (MIMO) antenna array is designed for fifth-generation (5G) mobile phones based on the theory of characteristic modes (TCM) of the composite perfect electric conductor (PEC) and lossy dielectric structures. First, the TCM of composite PEC-lossy dielectric structures is reviewed briefly. Then, the application of the theory for low-SAR antenna design is demonstrated through a four-antenna MIMO antenna array. Finally, the proposed MIMO array is fabricated, and its performance is measured. Its −10 dB impedance bandwidth can cover the desired frequency band from 3.4 to 3.6 GHz. The isolations between different antenna elements are higher than 15.4 dB. Their total efficiencies range from 81.3% to 89.9%. The envelope correlation coefficient (ECC) is lower than 0.07. The 10 g spatial-average body SAR corresponding to the situation that four antennas simultaneously radiate is 0.47 W/kg. Compared with the state-of-the-art 5G MIMO antenna arrays, the proposed MIMO antenna array has the lowest peak SAR value, satisfactory efficiency, isolation, and ECC. This article provides a general methodology for the design of low-SAR mobile phone antennas.