A Practical Guide to Optimal Impedance Matching for UHF RFID Chip

This paper shows that the classical conjugate impedance matching used in the UHF RFID is not optimal anymore with new chips that have high sensitivity. The optimal matching allowing to maximize the read range of an RFID system (reader and tag) is introduced. The principle relies on finding the optimal trade-off between the power received by the tag and the modulated power backscattered to the reader. This matching depends on both tag and reader parameters. The proposed method is optimal and can be applied to any tag (passive and semi-passive). Compared to classical conjugate impedance matching, we show that this new approach can increase the read range by 22% and 8% in two examples: for a semi-passive tag based on Monza X8-K Dura chip and a passive tag based on Monza R6-P chip, respectively. Finally, a practical guide is proposed for antenna designers to optimize the matching in practical applications.