Direction Finding of RFID Tags in UHF Band Using a Passive Beam-Scanning Leaky-Wave Antenna

This work proposes a novel system for location applications of RFID tags in UHF band. The system is based on a frequency-scanning leaky-wave antenna (LWA), commodity hardware and Angle-of-Arrival (AoA) estimation of the signal reflected from RFID tags, by using only RSSI (Received Signal Strength Indicator) data. The LWA is completely passive, manufactured in simple printed technology and directly connected to the RFID reader. The dispersive nature of the LWA combined with the selection of a proper high permittivity substrate allows the radiation of frequency steered directive beams. The system is based on four directive beams created by the two-port antenna and two RFID channels to estimate the AoA by amplitude-monopulse signal processing and angular pseudospectrum technique. Thus, our approach is efficient, simple and low-cost, since the use of expensive or complex hardware required for electronic phased-array steering/beam-switching is avoided and the required computational load is low. Several experiments have been performed in different scenarios, reporting a wide FoV of 130°, multi-tag detection and a RMSE of 8,1°.