A Wideband Circularly Polarized Antenna with Wilkinson Feed Network for Worldwide UHF Band RFID Reader

摘要

A radio frequency identification (RFID) reader antenna with circular polarization (CP) radiation is proposed to operate at worldwide UHF band which covers 840-960 MHz. The size of the antenna is 0.555λ_0 × 0.553λ_0 × 0.099λ_0. A micro-strip patch with truncated corners as the main radiation patch is placed between the Wilkinson feed network layer and the parasitic patch layer. The ground plate is placed on the top of the feed network layer. The feed network is connected with the main radiation patch via two metal cylindrical probes which produce two orthogonal signals of equal amplitude and 90 degree phase difference. The proposed antenna has wideband circularly-polarization characteristics. The truncated corners on the main radiation patch can increase 3dB axial ratio (AR) bandwidth while improving the best axial ratio. And the parasitic patch can adjust the radiation direction of the antenna while increasing its gain. The simulation results show that the proposed circularly polarized UHF reader antenna has an input impedance matching bandwidth (S_(11) ≤ -10dB) of 456 MHz (675-1131 MHz), the band of reflection coefficient S_(11) ≤ -20 dB covering 842-955 MHz, 3-dB axial ratio bandwidth of 296 MHz (741-1037 MHz), minimum axis ratio reaching 0.33 dB, and the highest gain reaching 3.53 dBi in the operating frequency band. Both the impedance bandwidth and the axial ratio band cover the entire UHF band of RFID systems.