Reducing Hand Effect on Mobile Handset Antennas by Shaping Radiation Patterns

User interaction can significantly degrade handset antenna performances through frequency detuning and absorption. In this article, the relationships between the hand effects and the radiation patterns of the antennas are investigated using characteristic mode theory. First, we calculate the characteristic far fields of a typical monopole-loaded handset antenna with metal frames. Afterward, the radiation patterns of the handset antenna are simulated and obtained in two different scenarios, i.e., in free space and with hand. Then we map the antenna patterns in two scenarios to the characteristic mode patterns by calculating the weighting coefficients, which stand for the power contributions of the modes. By inspecting the variations of the weighting coefficients in free space and with hands, it is found that the modes with less radiation at the boresight and the backward directions are more robust to the hands. Accordingly, a handset antenna with little radiating power toward the boresight is designed. Compared to the reference antenna with the same feeding location, the efficiencies of the proposed antenna have been improved by 4.1 and 6.3 dB, respectively, for the left-hand and right-hand scenarios. Experiments have been carried out for the hand effects, with the measured results agreeing reasonably with the simulated ones.