Calibration-Free Chipless Radiofrequency Identification Tags with Enhanced Data Capacity

In this paper, a chipless radiofrequency identification (RFID) tag that requires no additional radar-cross section (RCS) calibration is proposed. The proposed tag shows the potential for the enhancement of data capacity as high as 22.1 bits. As compared to most of the chipless RFID tag in the literature, the proposed tag shows a distinct feature that it does not need to determine a clutter response in the first place. Such a calibration-free characteristic is implemented thorough a temporal separation detection using short-time Fourier transform (STFT). The high capacity is obtained through a designed spectrum over 2.0-6.0 GHz. The proposed tag consists of four resonators. Each resonator uses two strips forming into a right triangle with a back conductor. By varying the location of the split locations, the resonant frequency of the cross-polarization backscattering can be controlled. Summarizing the controllable states for the four resonators, high capacity is thus obtained. Measured results show that the ID of the tag can be detected without calibrating the clutter response.