High Head–Hand Efficiency and Low-SAR Mobile Phone Antenna Design Based on Unidirectional and Uniform Current Distribution

Abstract

A high head-hand efficiency and low-SAR mobile phone antenna is proposed in this article. The impact of the antenna’s current distribution on its efficiency and spatial-average specific absorption rate (SAR) is analyzed, revealing that unidirectional and uniform current distributions on the antenna can achieve a dual benefit of high head-hand efficiency and low-SAR values. Based on this idea, a double loop antenna consisted of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\lambda $ </tex-math></inline-formula> outer loop with differential feed and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\lambda $ </tex-math></inline-formula> inner loop with coupled feed is designed, which can implement unidirectional and uniform current distribution in a wide frequency band. The measured −6 dB impedance bandwidth of the proposed antenna can cover 1710–2690 MHz. Its measured average head-hand efficiency from 1710 to 2690 MHz is −5.3 dB (29.5%). Its simulated normalized peak head and body SAR values are lower than 1.0 W/kg.