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

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 $50 \Omega$ 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 860 MHz to 880 MHz, covering the lower band UHF RFID frequencies in the European Telecommunications Standards Institute (ETSI) region.