Design of Koch Fractal Circularly Polarized Antenna for Handheld UHF RFID Reader Applications

In this study, a novel design of circularly polarized antenna based on Koch fractal geometry is presented and experimentally investigated. Circular polarization and size reduction are achieved by placing two asymmetric Koch fractal geometries on x- and y-planes of the single-probe-feed square radiator. Further, to tune resonant frequency around the 911-MHz, four arrow-shaped slots are inserted in diagonal axes of the square radiator. It is perceived that compact size of the antenna can be achieved by increasing the overall size of the arrow-shaped slots and indentation angles of Koch fractal geometry. The antenna is fabricated on FR4 substrate with a size of
$54 \times 54 \times 1.6\,\text{mm}^3$
(
$0.162 \lambda_{0}\times 0.162 \lambda_{0}\times 0.0048 \lambda_{0}$
at 900 MHz) and tested to validate the proposed design. The 3-dB axial-ratio bandwidth and impedance bandwidth of the proposed antenna design are found to be 8 MHz (907.0–915 MHz) and 37.0 MHz (891.0–928.0 MHz), respectively. The measured results confirm that the proposed design covers US radio-frequency identification (RFID) band (902–928 MHz) and can be used for RFID short-range reading applications.