A transmitter beamforming system for the localization of passive RFID tags

In this paper, a new approach for estimating the position of a passive UHF RFID tag is presented. Instead of using well known angle-of-arrival (AoA) techniques, a transmitter beamforming method, called ‘Angle-of-Activation’ (AoAct) is applied. By pivoting the main lobe of the interrogator's three element transmitter antenna array and utilizing the very sensitive response threshold of passive UHF RFID tags, the tag direction is estimated. This is performed by appropriately adjusting the I and Q components of the complex baseband phasor of each channel. In comparison to analog techniques, this new approach delivers a higher angular resolution and better direction accuracy. Applying this technique from different spatially distributed stations, the tag position can be estimated by triangulation. Experiments with the AoAct localization system were performed showing that an average localization accuracy of 10–20 cm even in a typical multipath environment can be achieved.