Abstract: Systems and techniques for reading radio frequency identification (RFID) tags and determining the distance between a reader and a tag being read. A plurality of interrogation signals are transmitted to an RFID tag, with signals at a first frequency being transmitted at a plurality of antenna polarizations and signals at a second frequency being transmitted at a plurality of antenna polarizations. The antenna polarizations are chosen such that return signals resulting from the signals and traveling along reflective paths will sum to zero. Return signals received from the tag are averaged, and phase shift information exhibited by the return signals is determined. The phase shift information for the return signals and frequency information for the interrogation signals is used to compute the distance between the reader and the tag.

Abstract: Systems and techniques for reading radio frequency identification (RFID) tags and determining the distance between a reader and a tag being read. A plurality of interrogation signals are transmitted to an RFID tag, with signals at a first frequency being transmitted at a plurality of antenna polarizations and signals at a second frequency being transmitted at a plurality of antenna polarizations. The antenna polarizations are chosen such that return signals resulting from the signals and traveling along reflective paths will sum to zero. Return signals received from the tag are averaged, and phase shift information exhibited by the return signals is determined. The phase shift information for the return signals and frequency information for the interrogation signals is used to compute the distance between the reader and the tag.