Radio frequency transponder system

摘要

Disclosed is a radio frequency transponder including a substrate and a plurality of planar antennas (2002) on the substrate. Each antenna (2002) has a shape that determines a corresponding resonant frequency of the antenna (2002). The antenna causes a phase difference between backscattered signals generated in response to excitation of the antenna (2002) by orthogonally polarised interrogation signals at the resonant frequency. The phase difference represents a code of the antenna and the antennas (2002) each have respective different resonant frequencies. The codes are determined from the phase differences between the backscattered signals at each of the resonant frequencies are used to generate a unique code for the transponder.