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 degrees 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 degree to 360 degree in azimuth, and -40 degree to 40 degree in zenith. The minima of the antenna's AR beamwidth follows the peak gain direction, giving an equivalent 3 dB AR beamwidth of 136 degree for every phi cut, wider than current state-of-the-art. Moreover, the proposed antenna array presents a 50 Ohm 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.