Imaging RFID system at 24 GHz for object localization

A new RFID system for the ISM band at 24 GHz employing quasi-optical beam forming is presented. Active integrated antennas are used as transmitters resulting in exceptionally small size of the ID-tags. Identification codes are transmitted via a spread-spectrum modulated subcarrier that allows for very simple free running microwave oscillators as well as simple but highly selective receiver concepts. A dielectric lens and a 5/spl times/5 rectenna array comprise an imaging receiver that not only identifies but also localizes the tags with an angular resolution better than 3/spl deg/ at a distance up to 14 meters.