A simple UHF RFID circularly-polarized reader antenna is presented in this paper. Air-substrate patch antenna is used to design. Truncated patch structure and shorted posts are used to obtain circularly-polarized characteristic. Measured results show that the antenna with size of 254∗254∗18 mm, has an impedance bandwidth of 880–960 MHz for voltage standing wave ratio (VSWR) less than 1.5. Moreover, axial ratio (AR) with bandwidth of 906–928 MHz is under 3dB. A good agreement is achieved between simulated and measured results. The antenna is a good choice for UHF RFID applications.
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