Design of a Multipolarized RFID Reader Antenna for UHF Near-Field Applications

This paper presents our investigation into a novel ultrahigh-frequency (UHF) radio frequency identification (RFID) multipolarized reader antenna based on a pair of symmetrical meandering open-ended microstrip lines for near-field applications. The near-field and multipolarization operation is achieved by introducing a 90° phase shift between the currents flowing along the opposite side of two branches. The proposed antenna is shown to generate a uniform and strong electric field in its near-field region within a reading volume: 450 mm x 450 mm x 350 mm (width x length x height). The simulated and measured impedance bandwidths (-10 dB) agree very well, ranging from 825 to 965 MHz and covering the UHF RFID standard. In addition, it exhibits a low far-field gain, avoiding to misreading the tags outside the near-field region. The fabricated antenna was fully tested with multiple tag antennas that are placed in different orientations and even in a conveyor system, demonstrating a 100% reading rate of arbitrarily oriented tags within the reading zone.