System modeling of the RFID contactless inductive coupling using 13.56 MHz loop antennas

This paper presents a novel model of the inductive coupling using loop antennas and occuring in HF-RFID or NFC systems. It takes into account the coupling coefficient, the chip/antenna matching and the characteristics of the two resonant circuits (the transmitter and the receiver) constituting an NFC system. The model shows that maximum coupling between reader and tag antennas and conjugate impedance matching between the antenna and the chip are not always the best choices for a reliable transmission in the desired operating area.