This study developed a miniature tag antenna attached to a backing metal for ultrahighfrequency radio frequency identification (RFID) applications. The impedance of this antenna can be easily controlled at the desired fixed frequency by using different mechanisms and was not considerably affected by backing metal size. This antenna comprises a radiating patch with double I-shaped slots and a ground layer shorted to a narrow inductive plate. Loading a closed slot in the center of the patch and the open slits enabled flexible frequency tuning to match the complex impedance of the microchip used. This tag antenna has a low profile of 28.02 × 25.02 × 2.61 mm 3 (0.086 × 0.076 × 0.0079 ), and it provides a high power transmission coefficient of 99.74%, realized gain of −2.3 dB, and a reading distance of 8.1 m when it is located at the center of a metallic plate of size 250 × 250 mm 2 . The operational frequency of the proposed antenna was designed to reside the frequency bands for North and South America respectively). Measurements of the antenna prototype proved that the experimental results agreed with the simulated data.INDEX TERMS Metallic tag antenna, shorted inductive plate, reading distance, RFID tag, I-shaped patch.
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 Cshaped 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 mm 3 (0.092 λ 0 × 0.092 λ 0 × 0.0092 λ 0 ) 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 mm 2 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.
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