Compact Hybrid Dipole-Loop Antenna for On-metal UHF RFID Tag Design

A hybrid dipole-loop antenna, which is constructed by connecting a dipole with a loop, is proposed for designing a compact metal-mountable RFID tag. Here, a pair of dipole arms are closely integrated with a rectangular loop for achieving a compact size of 60 mm × 30 mm × 2 mm. Also, a rectangular patch is tactfully placed at the center of the loop for tuning down the tag resonant frequency to the desired UHF passband. Conjugate impedance match is achievable between the antenna and the chip by tuning the dimensions of the dipole arm and the rectangular patch. The proposed tag antenna can achieve a realized gain of −1.182 dBi in the boresight direction, which is equivalent to a read range of 15.3 m, as estimated using the Friis’ transmission equation.