Beam Scanning UHF RFID Reader Antenna With High Gain and Wide Axial Ratio Beamwidth

Abstract

A novel ultra-high-frequency (UHF) RFID reader antenna with 2 dimensional (2D) beam-scanning capability and a wide 3 dB axial ratio (AR) beamwidth of over 136 • is presented. The proposed antenna consists of three concentric metal rings, each having a branch wire to stimulate circular polarization (CP) and a separate feed. The antenna is able to perform a 2D beam-scan with a relatively stable gain (9-11 dBic) from 0 • to 360 • in azimuth, and-40 • to 40 • in zenith. The minima of the antenna's AR beamwidth follows the peak gain direction, giving an equivalent 3 dB AR beamwidth of 136 • for every phi cut, wider than current state-of-the-art [1]. Moreover, the proposed antenna array presents a 50Ω impedance with no impedance matching network, and requires only two phase shifters to steer, significantly reducing the design complexity. The antenna's-10 dB return loss bandwidth is from 843 MHz to 880 MHz, covering the lower band UHF RFID frequencies in the European Telecommunications Standards Institute (ETSI) region.