A Minkowski Fractal Circularly Polarized Antenna for RFID Reader

A design of fractal-like antenna with circular polarization for radio frequency identification (RFID) reader applications is presented in this article. The modified Minkowski fractal structure is adopted as radiating patch for size reduction and broadband operation. A corner-truncated technology and a slot-opened method are employed to realize circular polarization and improve the gain of the proposed antenna, respectively. The proposed antenna is analyzed and optimized by HFSS. Return loss and maximum gain of the optimized antenna achieve to -22.2 dB and 1.12 dB at 920 MHz, respectively. The optimized design has an axial ratio (AR) of 1.2 dB at central frequency of 920 MHz and impedance bandwidth (S11<=-10 dB) of 40 MHz (4.3 %). Its input impedance is (57.9-j2.6) W that is close to input impedance of coaxial line (50 W). Numerical results demonstrate that the optimized antenna exhibits acceptable performances and may satisfy requirements of RFID reader applications