Improved UHF RFID localization accuracy using circularly polarized antennas

We present the design of two new antennas for an indoor angle-of-arrival based passive UHF RFID tag localization method. First, a circularly polarized patch antenna that can be used as the reader´s transmit antenna or as the tag antenna. Second, a circularly polarized three-element patch antenna array for the reader. We use measurements in a 3 m × 3 m test grid with 25 equally spaced measurement points, placed into a standard office room, to show that the new antennas improve localization accuracy by 53% compared to a system equipped with linearly polarized antennas. The new circularly polarized system is able to localize a tag in our setup with a measured mean error of 9 cm and a measured mean standard deviation of 7 cm.