UHF RFID impedance matching: T-match-dipole tag design on the highway

Impedance matching is a constant topic in the RFID community. However, it still heavily depends on the trial-and-error approach, even for the popular T-match. In this paper, T-match-dipole tag designthe dynamics behind the impedance matching of T-match-dipole tags are studied systematically. Based on the inductance-based model stemmed from the transmission line model, the bandwidth characteristics of diverse matching scenarios are discussed. Closed-form expressions of the maximum bandwidths and the relevant conditions are provided. In particular, a special doubletuning scenario called the degenerated double-tuning is explored for the first time. Guided by the conditions of the maximum bandwidths, efficient design approaches are proposed for the embedded T-match dipole. Results of multiple design examples demonstrate the usefulness of the impedance matching theory and the design approaches presented.