A fast method to design and characterize the performance of UHF RFID tags

In this work, we present a direct method to measure the antenna impedance for balanced Ultra High Frequency (UHF) Radiofrequency Identification (RFID) antennas. The measurement setup is composed of a Short-Open-Load-Thru (SOLT) calibration kit, a mid Vector Network Analyzer (VNA), and a custom differential probe. After the calibration using the custom kit, a mixed S-parameter model is used to obtain the antenna impedance directly from the VNA, without post-processing. The proposed procedure has been validated by measuring successfully two antenna models for two fabrication techniques. Results are very close to the obtained by simulation, validating this technique as a useful tool to study antenna response.