UHF RFID Transponder Chip and Antenna Impedance Measurements

The communication performance between reader and transponder in radio frequency identification (RFID) in the ultra high frequency (UHF) range strongly depends on the matching between transponder chip and transponder antenna. To assure power optimization in the forward link the input impedance of the antenna must be the complex conjugate of the chip’s input impedance. In this contribution a measurement method is introduced to determine the transponder chip’s input impedance in absorbing mode versus chip input power. A prematching test setup with impedance tuners assures high measurement accuracy. Additionally, an antenna is presented which is designed to perfectly match the chip. Its input impedance is simulated and measured versus frequency. Finally, the matching between chip and antenna is calculated in terms of a power transmission coefficient.