Design of Low-SAR Mobile Phone Antenna: Theory and Applications

This paper focuses on the design of low specific absorption rate (SAR) mobile phone antennas. Firstly, The interaction mechanism of the radiation fields of mobile phone antennas with nearby human tissues is analyzed by using boundary conditions of electromagnetics. The relations between SAR and the electric field is constructed. Then a concept of reverse current is proposed to decrease the electric field radiated by the antenna at the air-tissue interface, consequently reduce the SAR of human tissues. Finally, a metal-rimmed mobile phone antenna is designed according to the proposed theory. The ground clearance of the designed antenna is 2 mm. Their measured normalized peak head and body SAR values are lower than 1.0 W/kg, much less than the SAR safty limit of 1.6 W/kg according to the guidelines of IEEE and FCC or 2.0 W/kg according to the guidelines of ICNIRP. The measured -6 dB impedance bandwidths are 830–1040 MHz and 1670–2730 MHz, respectively. The measured efficiencies are higher than -5 dB at the lower band and -4 dB at the higher band. The measured results prove that the proposed theory can provide a guidance for the design of low-SAR mobile phone antennas.