A dual frequency radio tag for a radio frequency identification system is provided that includes an antenna system and a first receiver coupled to the antenna system. The first receiver receives and processes request signals from a first unit type at a first frequency. A second receiver is coupled to...http://www.google.com.hk/patents/US7271727?utm_source=gb-gplus-share專利 US7271727 - Dual frequency radio tag for a radio frequency identification system
