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.