A broadband circularly polarized antenna of square-ring patch for UHF RFID reader applications

A circularly polarized, broad bandwidth, square-ring patch antenna for radio-frequency identification (RFID) is proposed. The antenna has a dimension of 100 × 100 × 22.9 mm3. By using a Wilkinson power divider and a patch-antenna structure, a measured 3-dB axial-ratio bandwidth of approximately 140 MHz (16.47%), an impedance bandwidth of 136 MHz (15.81%), and a measured peak gain of approximately 6.8 dBic are being achieved. The operating band of the proposed antenna is suitable for China (840–846 MHz), Europe (865–868 MHz) and the United States (902–928 MHz) ultra-high frequency (UHF) RFID applications.