Design of Dual Band HF-UHF RFID Tag Antenna for Metal Surface Application

Lim, Jia Jie (2024) Design of Dual Band HF-UHF RFID Tag Antenna for Metal Surface Application. Masters thesis, Tunku Abdul Rahman University of Management and Technology.

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Abstract

This thesis presents the design, optimization, and analysis of compact, low profile, electrically small, dual-band RFID tag antennas for High Frequency (HF) and Ultra High Frequency (UHF) applications through simulation-based studies. An EM4425 microchip was successfully incorporated, ensuring impedance matching at both 915 MHz and 13.56 MHz. Parametric simulations demonstrated the impact of geometrical parameters on resonance frequency, radiation efficiency, and realized gain. Two flexible single-sided rectangular polyimide inlay pieces are folded to form the three conductor layers structure of the proposed tag antenna. At UHF, the tag achieved excellent conjugate matching, with a realized gain of 0.73 dBi, a return loss of -21.6 dB, and a power transmission coefficient of 0.99. In HF applications, the coil antenna exhibited reliable performance within 1.5 cm. Further optimization using simulation involved a three-layer flexible polyimide structure with a slow wave design for UHF tuning and Polypropylene (PP4) foam as a separator to minimize interference. Adjustments to slot1 length and middle layer patch length enhanced the UHF tag’s performance, achieving a return loss of -36.08 dB, a radiation efficiency of 56%, and a realized gain of 3.29 dBi, resulting in a read distance of 5.8 meters. The HF coil antenna’s dual-layer design reduced the number of coil turns while maintaining strong magnetic field strength up to 4 cm. Using CST Studio Suite (CST) and Advanced Design System (ADS), extensive simulations further studies with dual-simulation, achieving a return loss of -26.79 dB, a radiation efficiency of 54%, and a realized gain of 2.98 dBi with a read distance of 5.6 meters. For HF applications, the coil antenna ensures consistent magnetic field performance within 3.5 cm. These simulation-based results highlight the proposed tag's suitability for conventional RFID systems, particularly in challenging environments with metallic surfaces.