A compact UHF RFID tag antenna using split-ring-resonator-loaded short dipole

An compact uniplanar tag antenna for UHF radio-frequency identification (RFID) applications is proposed based on a split-ring-resonator- (SRR-) loaded short dipole. The antenna exploits the magnetic resonance of the SRR, and the split of the SRR is replaced by an interdigital capacitor to lower its resonant frequency. The proposed antenna has a relatively compact size, simple uniplanar structure, and systematic design procedures to achieve conjugate matching to various tag chips. A prototype antenna of area 35 mm × 18 mm is designed for the Alien H3 RFID tag chip and fabricated. Its maximum read range is measured to be about 190 cm, which is longer than that of a commercially available tag of similar size under the same setup.