Compact Single-Layer RFID Tag Antenna Tolerant to Background Materials

Simple and low cost tag antenna with long reading distance in various environments is in great demand with its wide applications. This paper describes the design and optimization procedure of a single-layer tag antenna, which covers relatively long reading range when mounted on both metallic surface and various dielectrics. The antenna is based on the loop structure, with a small ka of 0.66. Characteristic mode analysis is first performed to inspect how a typical loop structure radiates in free space and on PEC. Antenna structure is then designed based on the characteristics of the loop. Afterward, equivalent circuits of the tag antenna on dielectrics and on metal are extracted, in order to provide guidance for antenna optimization. The proposed tag antenna achieves the maximum reading distance of 6.1 m and 14.1 m, respectively, when mounted on metal and dielectrics with low permittivity. Measurements of the tag antenna were carried out in different environments, including outdoor scenario, indoor scenarios with low and high reflections. The measured results agree reasonably well with the predicted ones. The tag antenna is proved to be competitive in perspective of simple structure, low cost, long reading distance, and tolerance on various background materials.