Metal-Tolerant UHF RFID Tag Antenna with a Comb-Shaped Design

A novel, miniature, and compact folded comb-shaped UHF RFID tag antenna for metal objects is introduced. The design features a comb-shaped patch with multiple slots and a stub-integrated radiating element, minimizing the effects of reflected waves. The slots lower the resonant frequency of the folded patch, while the comb-shaped patch is grounded through a single shorting stub that provides inductive tuning for frequency adjustment. Constructed on a flexible polyethylene terephthalate substrate, the tag has dimensions of only 30 mm × 30 mm × 1.71 mm (0.092λ × 0.092λ × 0.0052λ at 919.6 MHz). Its simple yet innovative structure enable effective conjugate matching with the chip, achieving adequate resistance and inductive reactance. When mounted on a 20 cm × 20 cm metal plate, the tag antenna achieves a power transmission coefficient close to 1 and a maximum read range of 7.47 m with an EIRP power of 4 W.