Miniature Folded Patch With Differential Coplanar Feedline for Metal Mountable UHF RFID Tag

In this paper, a pair of differentially fed coplanar waveguides is employed for exciting a folded patch antenna for designing a metal-mountable UHF RFID tag. The proposed tag has a compact size of 30 mm × 25 mm × 3.0 mm. Multiple slots are incorporated into the patch for tuning the resonant frequency and optimizing the impedance matching between the chip and the antenna. Two inductive stubs are introduced at two corners of the radiating patch to enable further frequency tuning. An equivalent circuit has been given for characterizing the tag's impedance characteristics. When tested on a 20 cm × 20 cm metal plate, the read range of the proposed tag can achieve 8.9 m (4 W EIRP) using the Monza R6 microchip (with chip sensitivity of -20 dBm). Also, it has been found that the resonant frequency of the proposed tag antenna is stable and it does not shift much when the size of the backing metal is varied. The read distance is also more than 4 m when the proposed tag is attached to various dielectric materials with permittivity ε
_r
in the range of 1-12.4.