Patent ID: 8248210

Claim:
A method of determining spatial information about an object coupled to one or more RFID tags using one or more receiving antennas at an RFID reader, comprising: transmitting one or more RF inquiries to the one or more RFID tags at a first time; measuring a phase for each RFID tag's response at each of the one or more receiving antennas; calculating a phase difference between the measured phases of each response for two or more tag-and-antenna pairs; determining a first set of equations based at least on a distance formula applied between each tag-and-antenna pair distance and a corresponding phase difference; determining a second set of equations based at least on the distance formula applied between each antenna-pair distance and known antenna spacings or between each tag-pair distance and known tag spacings; and solving the first set of equations and the second set of equations to generate location coordinates for the one or more RFID tags, wherein the first set of equations is given by ∥R rm −T tm ∥−∥R rn −T tn ∥=KΔφ, wherein R rm = [ x rm y rm z rm ] is an antenna location of each antenna rm; T tn = [ x tn y tn z tn ] is a tag location of each tag tn; M is a first total number of antennas; N is a second total number of tags; K equals λ/4π; λ is a wavelength of transmission of an RF inquiry; Δφ is a phase difference of phases measured at the antennas; 1≦rm,rn≦M; 1≦tm,tn≦N; and further wherein if tm equals tn, rm does not equal rn, and if rm equals rn, tm does not equal tn.