Pattern reconfigurable UHF RFID universal reader antenna array

In response to the rising demand for adaptable and versatile RFID reader antenna, this paper presents an integrated reader system featuring an array of four antennas. The primary objective is to design four identical, circularly polarized, high-gain, wide-band antennas that cover the 860-960 MHz UHF RFID band. Each antenna consists of three layers, the radiator and director layers, designed as patch antennas with trimmed edges and a central slot, while the reflector layer is constructed from a copper material. These layers are assembled with four Teflon spacers, and a coaxial connector is utilized for feeding the antenna. An open-circuit stub is used to improve impedance matching. CST Microwave Studio was employed for design optimization. The four sector antennas achieve a 150 MHz bandwidth (833-983 MHz) and a maximum gain of 8.4 dBi. When combined with a four-port RFID reader (ThingMagic M6E), the antenna system generates four electronically switchable beams in the azimuth plane. The proposed antenna exhibits lefthand circular polarization (LHCP) within the RFID ISM band, maintaining an axial ratio (AR) between 1 dB and 3 dB. The antenna array, including the reader and control unit, measures 255 x 255 x 210 mm. Simulation and measurement results confirm the system's performance and functionality.