Finite Element Simulation of Impedance Measurement Effects of NFC Antennas

In this paper, the problem of connecting the unbalanced measurement setup on the balanced antenna of the near-field communication (NFC) system is addressed. The parameters of the antenna's equivalent circuit were determined using quasi-static and full-wave vector field finite element simulations. Measurements and simulations are carried out on three different prototypes of 13.56 MHz NFC rectangular four turns antenna printed on FR4 substrate material. The obtained results concerning the RLC equivalent circuit parameters show that a direct connection of the unbalanced measurement devices to the balanced antenna structure impairs the accuracy of the obtained measurement data because of the mode mismatch at the antenna terminals.