PLANAR COMPACT OMNIDIRECTIONAL TAG ANTENNA WITH CIRCULAR POLARIZATION FOR UHF RFID SYSTEM

摘要

A novel compact design of planar circularly polarized (CP) tag antenna for the UHF RFID system is proposed. By introducing the Y-shaped slit as the feed structure, the measured half-power bandwidth of the proposed CP tag antenna can be more than 135 MHz (865 ～ 1000 MHz), which includes the entire operating bandwidth for worldwide the UHF RFID system. The obtained 3 dB axial-ratio (AR) bandwidth can be about 13 MHz, which is suitable for Taiwan UHF RFID applications. The proposed tag antenna reduces the antenna size by at least 11.4% since the antenna size is only 40 × 40 × π mm~2. Meanwhile, with omnidirectional reading patterns, the measured reading distance is about 7.2 m. Good tag sensitivity was obtained across the desired frequency band.