A Low Profile Printed Quadrifilar Helical Antenna for Handheld UHF RFID Reader

This paper proposes a compact printed quadrifilar helix antenna (PQHA) that has quarter wavelength inverted-F resonators at a low cost. The proposed PQHA is fed by a four-port quadrature phase system which consists of a 180 degrees degrees power splitter and two couplers implemented by lumped-element circuit. The fabricated and miniaturized PQHA measures only 60 x 60 x 27 mm(3).The measured impedance bandwidth is about 21% and the 3-dB axial ratio bandwidth range from 800-1000MHz can cover the whole UHF RFID bands. The measured maximum gain is around 3.6dBic and the 3-dB beam width is about 120 degrees at 920 MHz, which small size and good performance is enough for practical handheld RFID applications.