Compact shorted C‐shaped patch antenna for ultrahigh frequency radio frequency identification tags mounted on a metallic plate

Abstract

This paper describes an ultrahigh frequency (UHF) tag antenna mounted on a metallic plate for radio frequency identification (RFID). The impedance of the proposed antenna can be tuned using various methods. The compact patch antenna consists of a C-shaped resonator and a ground plane connected to a small shorting wall and is connected to a feeding loop in the middle of the C-shaped resonator. Etching a couple of slits close to the shorting wall and a slot in the center of the C-shaped resonator provided a flexible method for adjustment to match the conjugate impedance with the UCODE 8/8 m chip (13 − j191 Ω at 915 MHz). The optimal design with an overall size of 30 × 30 × 3 mm3 (0.092 λ0 × 0.092 λ0 × 0.0092 λ0) yielded a high power transmission coefficient of 91% and reading range of 6.4 m for the effective isotropic radiated power (EIRP) of 4.0 W when the tag antenna was mounted on a 220 × 220 mm2 metal plate. The proposed antenna was designed at standard frequency bands of the Federal Communications Commission (FCC, 902-928 MHz) for North America and Taiwan. Antenna fabrication and testing were performed, which revealed that the measured data were in good agreement with the simulation results.