US Patent 9645234 RFID device, methods and applications

Systems and methods for ranging in indoor environment that are accurate and that are substantially undisturbed by multipath interference. The method includes illuminating a sensor tag with electromagnetic radiation generated from a transceiver; the transceiver are being located a distance away from the sensor tag; the sensor tag comprising at least one nonlinear transmission line (NLTL) for broadband harmonic generation, receiving backscattered electromagnetic radiation from the at least one NLTL at three or more locations; coordinates of the three or more locations being known, obtaining from the phase and magnitude outputs at a second harmonic and at least one sub harmonic of second harmonic, a distance from the sensor tag to each of the three or more locations and trilaterating a location of the sensor tag.