A transponder location and tracking system having a phased array antenna mounted at a toll collection station includes a plurality of antenna array elements for receiving a signal from a transponder mounted on a vehicle and for providing a plurality of antenna element electrical signals. A plurality...http://www.google.com.hk/patents/US5227803?utm_source=gb-gplus-share專利 US5227803 - Transponder location and tracking system and method
