Design of UHF-RFID tags based on the T-match network

This paper is focused on the design of global band UHF-RFID tags based on the T-match network. Recently, a systematic method for the design and synthesis of global band UHF-RFID tags using such a matching network has been proposed (G. Zamora et al., IEEE Trans. Microw. Theory Tech., 61, 4090-4098, 2013). The reported design strategy is based on the required equivalent-circuit network for bandwidth maximization in single resonant UHF tags with conjugate matching, obtained in (G. Zamora et al., IET Microwave Antennas and Propagation, 7, 788-794, 2013). Such strategy requires the antenna to be previously designed to exhibit a self-resonance at the intermediate frequency of the UHF-RFID band, f₀. According to the first abovementioned reference, the value of the antenna resistance at the resonance must be much greater than a certain lower limit that only depends on the elements of the chip equivalent-circuit model. However, the great majority of the commercial UHF-RFID tags, which takes advantage of the T-match network, are based on dipole antennas, which exhibit a resistance value at the half wavelength resonance (typically around 73 Ω) close to the lower limit given by the RFID integrated circuits available on the market today.