Compact circularly polarized tag antenna for UHF RFID system

This work describes a novel compact design of planar circularly polarized (CP) tag antenna for UHF RFID system. By introducing the meander strip into the right-arm of the square-ring structure, the measured half-power bandwidth of the proposed CP tag antenna can be more than 100 MHz (860 ~ 960 MHz), which includes the entire operating bandwidth for worldwide UHF RFID system. The obtained 3 dB axial-ratio (AR) bandwidth can be about 33 MHz (902~935 MHz), suitable for American (902~928 MHz), Euro (918~926 MHz) and Taiwan UHF RFID (922~928 MHz) applications. Since overall antenna dimension is only 54 × 54 mm², the proposed tag antenna in this study can operate with antenna size reduction of 42 % than conventional CP antennas. Meanwhile, with bidirectional reading pattern, the measured reading distance is about 8.5 m. Good tag sensitivity is obtained across the desired frequency band.