Helical Antenna for Handheld UHF RFID Reader
In this paper, the authors describe a compact high gain circularly polarized antenna for handheld UHF RFID reader. The antenna is an axial mode helix operating in a backfire mode with ground plane on top and reflector on the bottom. The described antenna has small footprint (85 mm in diameter) and delivers maximum linear gain > 6 dBil, standing wave ratio < 2, and axial ratio < 2 dB in 60 MHz band centered around 895 MHz (Approximate bandwidth 7%). The antenna can be easily tuned to cover any desired portion of the global UHF RFID band (860-960 MHz). The antenna is an attractive solution for handheld readers to maximize tag read range while providing circular polarization. They also review existing antenna solutions for handheld readers and discuss link budget and forward and reverse link tradeoffs.