Low-SAR and High-FBR Patch Antenna With Small Ground Size for Wearable Devices

A high front-to-back ratio (FBR) microstrip patch antenna with small ground plane size is proposed and studied in this article. In order to suppress the serious back lobe brought by such a small ground, a hybrid loading technique consisting of coupled branch (CB) and resistor-loaded ground slot (RLGS) is introduced. Through the hybrid loading, extra magnetic currents on the ground are excited, by which the backward radiation of the original patch could be cancelled. In addition, the joint regulation mechanism of CB and RLGS is expressed as an equivalent circuit model, which provides more physical insight. The realized FBR of the proposed antenna reaches over 38 dB, as a result, the specific absorption rate (SAR) of the antenna under wearable conditions is suppressed, and the radiation efficiency is nearly unaffected by the human body, which is highly demanded by wearable devices.