Design of circularly polarized tag antenna with artificial magnetic conductor for on-body applications

Abstract

This paper presents a circularly polarized tag on a 3 × 3 AMC structure to obtain longer read range for UHF RFID on-body applications. A modified T-matching transformer is employed to achieve conjugate matching with the Monza 4 microchip. To overcome the influence of lossy human body, a cross-dipole tag antenna is directly implemented on the phase-dependent AMC structure to achieve high gain and isolate the influence of the human body. Then, the tag is pasted on a lossy human model to investigate its performance. The study finds that the AMC can increase the antenna gain by 3.34 dB and help generate circularly polarized (CP) wave. The measured fractional bandwidth of impedance is 3.2% which can cover the UHF RFID bands of North America and Taiwan. The measured read range of the tag pasted on a human body reaches 15.7 meters when the reader has 4W EIRP, and the sensitivity of the microchip is −16.7 dBm.