Dual Antenna Coupling Manipulation for Low SAR Smartphone Terminals in Talk Position

A rigorous analysis of the concept of coupling manipulation utilizing two antennas suited to modern smartphone devices in talk position for voice calls is presented. By using the optimum relative phase between the elements, they can substantially reduce the specific absorption rate (SAR) but still maintain efficiency due to the splitting of power between them and by exploiting a suitable level of interelement coupling. The same antenna elements can still be used for multiple-input–multiple-output (MIMO) when not in talk position without heavily degrading their fundamental capacity limit, but this is of secondary importance. The concept could be applied to frequency ranges used in mobile communications from 1.8 to 6 GHz where the ground plane has sufficient form factor. Extensive simulations using two planar inverted-F antennas (PIFAs) operating at 2.4 GHz are carried out to demonstrate conceptually how two antennas can be optimized to reduce SAR by over 50% compared to a single antenna element. SAR reduction is maintained regardless of the user’s head composition and how they are handling the device in a talk position. Antenna prototypes are measured and compared to verify the capacity when the handset is used away from the body with two MIMO terminal antennas.