Folded tag Antenna based on U-shaped Impedance Matching Structure for On-Metal Application

A ultrahigh frequency (UHF) folded tag antenna based on U-shape impedance matching structure, which can be applied on metal surface is presented in this paper. The tag antenna consists of two layers, the upper layer adopts double-ring structure design, the outer ring is radiation patch and the inner is feed ring structure. The second layer concludes a U-shape impedance matching structure and metal ground. Two layers are connected by short stubs on both sides. The compact footprint of the antenna is 40mm×45mm×3.2mm (0.122λ×0.137λ×0.0097λ at 915MHz). Due to the U-shaped structure, the antenna can conjugate match with the microchip. The folding method is beneficial to miniaturization design, and make the antenna perform well on metal. When the tag antenna is placed on metal surface, the maximum theoretical reading distance is 3.6m.

I. Introduction

Ultrahigh frequency radio frequency identification (UHF RFID) technology is a contactless identification system which transmit data through radio frequency. In recent years it becomes popular in automated supply and unmanned management due to its long reading distance and low cost. When a conventional tag antenna is placed in metal or liquid environment, the directional characteristic、 impedance and gain will deteriorate[1]. It is crucial to design the miniaturized tag antenna which can work in both free space and metallic environment.