| Along with a widespread application of the RFID technology, the broadband circularly-polarized reader antenna has become a hot spot in the antenna research. The status of broadband circularly-polarized antenna study abroad and home is analyzed thoroughly and the achieving methods of the broadband circularly-polarized reader antenna are also studied in this paper. In view of the absent study of single feed broadband circularly-polarized antenna, two kinds of novel single feed broadband circularly-polarized antenna which can be used in the RFID reader system are designed: one is a monolayer single feed broadband circularly-polarized microstrip antenna of self-similarity fractal geometry. The proposed antenna has the S11≤-10 dB impedance bandwidth of 64.6% and the AR≤3 dB axial ratio bandwidth of 11.4%. However, the monolayer single feed circularly-polarized antenna in the correlative literature have the S11≤-10 dB impedance bandwidth of 1%~5% and the AR≤3 dB axial ratio bandwidth of 0.8%~1%; The other one is a multilayer single feed broadband circularly-polarized microstrip antenna with dissymmetrical U-shaped slot. The proposed antenna have the S11≤-10 dB impedance bandwidth of 14.6% and the AR≤3 dB axial ratio bandwidth of 6.5 % . However, the monolayer single feed circularly-polarized antenna in the correlative literature only have the S11≤-10 dB impedance bandwidth of 3.93%~9% and the AR≤3 dB axial ratio bandwidth of 1.9%~4%. |
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