Capacitors-loaded Dipolar Patch Antenna for UHF Tag Miniaturization

A novel UHF RFID tag antenna, which has a compact physical size of
$35\ \mathbf{mm}\ \times 30\ \mathbf{mm}\ \times 3.118\ \mathbf{mm} (0.107\lambda\times 0.092\lambda\times 0.0095\lambda)$
, is proposed for metal mountable applications. The tag structure itself is designed using a pair of dipolar patches that are being fed by two T-shaped feedlines. Here, one pair of lumped capacitors are inserted across the narrow gap between the patches for introducing additional capacitance to bring down the resonant frequency and miniaturize the antenna size. Also, the tag resonant frequency can be easily tuned by adjusting the lumped capacitances. Experimental results show that the proposed tag antenna can achieve a far read distance of 11.1 m when it is placed on a metal plate, being tested with an effective isotropic radiated power of 3.28 W. Even though the tag size is small, it can still maintain good read performance.