Design And Optimization Of Compact On-Metal Ultra High Frequency RFID Tag Antennas

Chiang, Shao Ming (2021) Design And Optimization Of Compact On-Metal Ultra High Frequency RFID Tag Antennas. Master dissertation/thesis, UTAR.

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Abstract

In this dissertation, two compact UHF RFID tag antennas have been proposed for metal-mountable applications. Lumped components have been incorporated into the flexible tag antenna structures for achieving tuning flexibility in a broad range. The dipolar patch antenna has been selected for both the tag designs. In the first project, the concept of inductive channel is introduced for tuning the resonant frequency of a bowtie dipolar tag antenna, which has a compact physical size of 50 mm  50 mm  3.38 mm (0.1447λ  0.1447λ  0.0098λ), for applying on metal surfaces. The narrow inductive channel, which is embedded with an external lumped inductor, is loaded on top of the dipolar antenna for achieving arbitrary tuning capability in a broad range. It has been found that the top-loading patch can enhance the fields of the dipole, and the inductive channel can regulate the current flows on the top-loading patch. By adjusting the channel width as well as the external inductance, the resonant frequency can be effectively adjusted without affecting the read performances of the tag much. Here, an equivalent circuit has also been constructed for analyzing the impedance characteristics of the proposed tag antenna. The proposed tag antenna can achieve a measured maximum reading distance of nearly 19 m at an effective isotropic radiated power of 3.28 W. It can be arbitrarily tuned to operate at any frequency in the UHF band by simply adjusting the lumped inductor’s value, without changing the antenna structure. The pr oposed antenna is found to be insensitive to variation in the backing metal plate, and its operating frequency does not fluctuate with the plate size. In the second project, a novel UHF RFID tag antenna, which has a compact physical size of 35 (0.107λ x 0.092 λx 0.0095 λ), mm x 30 mm x 3.118 mm is proposed for metal mountable applications. The tag structure itself is designed using a pair of dipolar patches that are being fed by two Tshaped feedlines. Here, one pair of lumped capacitors are inserted across the narrow gap between the patches for introducing additional capacitance to bring down the resonant frequency and miniaturize the antenna size. The proposed tag antenna has a simple structure and it can be made on the single surface of a flexible PET subs trate. Also, the tag resonant frequency can be easily tuned by adjusting the lumped capacitances. Experimental results show that the proposed tag antenna can achieve a far read distance of 11.1 m when it is placed on a metal plate, being tested with an eff ective isotropic radiated power of 3.28 W. Even though the tag size is small, it can still maintain good read performance. For both the projects, it has been demonstrated that lumped components can be introduced into the antenna structures for providing ad ditional reactance for miniaturizing the antenna size. By adjusting the values of the lumped components, the resonant frequency of the proposed tag antennas can be arbitrarily. structures With the introduction of the external lumped components, the antenna of the proposed tag antennas can be kept intact without the need of modification for achieving frequency, as a result, the Qfactor of the antennas can be maintained for achieving high radiation efficiencies. A tag antennas have been sim ll of the proposed ulated and analyzed. Experiments have also been conducted to prove the working principles. Good agreement is found between the simulation and measurement.

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