Electrically Small UHF RFID Tag Antenna Based on Inductively Coupled Resonant LC Tank

We introduce two LC tank based electrically small UHF RFID tag antennas with a stacked configuration ( $0.04 \lambda\times 0.04 \lambda\times 0.02\lambda$ ) and a coplanar configuration ( $0.08 \lambda\times 0.04\lambda$ ). The method of using a resonant LC tank to minimize the antenna footprint is analysed with the antenna equivalent circuit and the electromagnetic simulations. The performance of the proposed antennas are verified in the wireless measurement with a maximum read range of 3.2 m and 2.5 m of the stacked and coplanar ones, respectively. The influence of antenna size on its performance is analysed with a parametric studies. The results indicate that the antennas feature a readily scalable size-performance ratio that makes it easy to adapt the tag according to different application requirements.