A Compact Circularly Polarized Ring Patch Antenna for RFID Reader Application

A compact circularly polarized (CP) ring patch antenna for ultra-high frequency (UHF) band radio frequency identification (RFID) reader applications is proposed in this article. The antenna is composed of a square ring patch antenna, a coupled feeding structure with a 90
^◦
phase delay and a perturbation unit. To generate CP radiation, the coupled-fed structure with a 90
^◦
phase delay is placed on the inner side of the ring. A truncation is created on two opposite corners of the square ring patch to further enhance CP performance. The coupled feeding also ensures a good impedance matching. Simulated results show that the antenna has an impedance bandwidth (|S
11
| < −10dB) of 3.3% (900–930MHz) and a 3-dB axial ratio (AR) bandwidth of 1.2% (911–922MHz). The antenna exhibits a stable peak gain of 7.3dBic and has compact dimensions of 140mm × 140mm × 10.4mm.