Efficiency Improvement for Antennas in Folded Smartphones

Folded mobile handsets become prevalent nowadays, which pose unique challenges for antenna design. In this letter, a method for enhancing radiation efficiency is proposed for foldable smartphone antennas in both free space and user scenarios. A λ/2 parasitic branch is introduced on the secondary frame, which changes the reverse currents along the two frames to in-phase currents. As a result, the radiation efficiency in free space is improved. The mechanism is analyzed using an equivalent circuit model. To enhance the radiation efficiency in user scenarios, more currents are transferred to the secondary frame, which is further away from the hand. The current transfer is realized by adding a shorting strip at the proper location of the secondary frame. Consequently, the user effect is mitigated, leading to higher efficiencies. The method is effective for different kinds of antennas at different frequency bands. A prototype of a folded handset has been fabricated, with the measured results agreeing well with the simulated ones. The proposed method potentially contributes to the development of foldable smartphones.