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An inductively coupled feed method is explored to design UHF radio frequency identification tag antennas. An analytical model for the proposed feed structure is derived and used to perform simple and wideband impedance match between an antenna and a tag chip without any additional matching networks. The proposed design methodology is verified by comparing the calculations and measurements, which show good agreement.
(ProQuest: ... denotes formulae omitted.)
Introduction: As the frequency for radio frequency identification (RFID) rises into the microwave region, proper antenna design becomes more essential to maximise the RFID system performance [1]. Especially, for passive RFID tags, a perfect impedance match between an antenna and a tag chip is essential to power up the chip, and maximise the read range. Because of cost and fabrication requirements, tag antennas must be directly matched to the chip, which may have complex impedance different from 50O. Large capacitive reactance and small resistance are usually observed. Such chip impedance with high Q makes it difficult to design a matched antenna and narrows the impedance bandwidth of the antenna.
In this Letter, we explore a new design methodology to make efficient and wideband RFID tag antennas using an inductively coupled feed. In [2], the authors used the inductive coupling to boost up the input resistance of electrically small antennas. However, they used a genetic algorithm to optimise the antenna characteristics, and the results presented narrow bandwidth owing to the discrepancy between the matched and the resonant frequency of the antenna. To overcome this problem, we derive an analytical model for the inductively coupled feed and explore its impedance characteristics to achieve wideband impedance match between the...