Design of Compact Passive Tag Antenna for Practical RFID Applications

• The communication quality between an RFID tag and a reader in a RFID network, especially the parameters of the passive tag antenna such as reading range, directivity and return loss, is affected by several factors from the environment. For practical RFID application, since the environment is complex and volatile, these factors include metallic surface of products, absorptions and impacts from neighbor tag antennas like scattering and mutual coupling. In this paper, it consists of the analysis of impacts caused by these factors and the design of passive tag antennas with resonant frequency 915 MHz able to be used in practical RFID applications against those impacts. Comparing with former ones, the proposed antenna reduces the size of the tag antenna to approximately commercial standard (18 mm x 48 mm x 3 mm) by using certain structures applied in the unit cell of metamaterial or HIS, while the properties including directivity, return loss and input impedance are still appropriate for RFID applications. Simulation results from HFSS indicates that at 915 MHz, the return loss can be about 21 dB, as most of the power can be radiated into the space towards the receiver. Meanwhile, the input impedance Z(0) = 9.4738 + j143.9189 Omega, perfectly matching the impedance of the RFID chip placed on the top surface of the antenna. The above improved parameters play an important role in prolonging the reading range.

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