Inverse SAR approach for localization of moving RFID tags

This paper presents an inverse synthetic aperture radar approach for localizing standard UHF RFID transponders. The proposed method is a powerful option to estimate the positions of tags that pass RFID gates or read points. A priori information about the relative transponder trajectory, such as the speed of a conveyor belt or a trajectory created by a robotic arm or rotary table, is used to generate an inverse synthetic aperture. Sampled phase data from RFID signals which are backscattered to single or multiple antennas combined with the information on the relative RFID tag trajectory are used to reconstruct the tag´s absolute trajectory. The paper describes basic properties of synthetic apertures in RFID systems and methods of evaluating beam patterns based on array beam steering theory. Simulations of a conveyor belt scenario and test data acquired from an industrial rotary table transporting tagged objects are described. The experimental results prove that our novel method enables robust localization of moving RFID tags even in a severe multipath environment.