Analysis of UHF RFID Tag Antennas Using an Equivalent Circuit Approach

In this paper, we describe an equivalent circuit approach to analyze one of the most common UHF RFID tag antennas, a T-matched dipole. We derive analytically closed-form expressions for all three tag resonant frequencies (two for tag sensitivity and one for backscatter). We show using a practical tag example, a 70 mm x 14 mm antenna designed for various items, how an equivalent circuit model can be extracted and effectively used for understanding tag behavior and optimizing its performance. We also present experimental data that demonstrates good agreement with the model.