Post-Design Modifications for Impedance Matching of UHF RFID Tag Antenna

This paper proposes post-design modifications of a standard dipole antenna to match the footprint of different RFID chips while maintaining the impedance matching. A feeding gap of 4 mm is reduced to 0.6 mm to match the RFID chip's footprint. To address the analogy, two different methods are discussed including the placement of conducting pins over the dipole arms and addition of L-stubs to ensure the antenna's matching to the chip impedance with the reduced feeding gap. These modifications provide a simple and viable solution to the problem related to RFID chip footprint. The design is simulated using CST-MWS for NXP UCODE G2iL RFID chip with the impedance of 23-j224 Ω at 915 MHz. The results show a good agreement between the original design and proposed modifications with the bandwidth from 893.7 MHz to 936 MHz and the gain of around 2 dBi for all cases. The antenna is also studied for different chip impedance, where a coupled feeding dipole for HIGGS 3 RFID chip with the impedance of II-j162 Ω is used. The design is initially developed to match at 915 MHz and the gain of 0.158 dBi is obtained. The proposed post-design modifications can provide a universal UHF RFID antenna for any RFID chip footprint and impedance.