Circularly polarized passive UHF RFID Tag on Wall for Indoor Object Identification and Localization

In this paper, a square-shaped microstrip passive RFID tag suitable for wall mount in RFID localization systems is presented. The tag antenna is designed for the ultra-high frequency (UHF) band and is excited by a dual inset feed network to achieve circular polarization (CP). A cross slot is embedded in the square patch to reduce antenna size and extend CP bandwidth. Characterization in an anechoic chamber shows that the prototype´s operational frequency band is significantly shifted compared to the simulation results. Nevertheless, when tested in the laboratory hallway with a standard UHF RFID reader, the tag still provides good reading range and decent CP performance in certain degrees of rotation.