Chipless RFID System: High Spectral Efficiency Tag Design and Low-Cost Reader Development

To address the serious scarcity of spectrum resources in the era of global mobile traffic surge and reduce the frequency band conflict between chipless radio frequency identification (CRFID) systems and other application systems, this article presents a novel design of a CRFID tag with high spectral efficiency. The traditional I-shaped resonant structure is redesigned as a dumbbell-shaped resonator, which increases the quality factor of the resonant unit by concentrating local current density. Combined with the dual-polarized frequency band multiplexing, the tag achieves higher spectral efficiency and greater coding capacity. The proposed dumbbell-shaped tag achieves 16-bit coding within the$2-3.2$GHz band, corresponding to a spectral coding efficiency of 13.3 bits/GHz. Moreover, the tag exhibits excellent robustness: the coefficient of variation (CV) for each resonant frequency interval is only 7%, and the resonant peak fluctuation is limited to 2.7 dB. To facilitate the transition of the designed tag from laboratory research to practical applications, a low-cost S-band reader based on the frequency-modulated continuous-wave (FMCW) principle is also developed. The reader employs a simple architecture consisting of a signal generator, a mixer, an antenna, and a signal processor. A superheterodyne architecture downconverts the backscattered signal, and a Hilbert transform extracts the magnitude response to decode tag information. The experimental results demonstrate that the reader can accurately read the proposed dumbbell-shaped tag within 20 ms. This work provides a complete, practical solution for CRFID systems—from the tag to the reader—enhancing both the performance and cost-effectiveness of CRFID technology for large-scale Internet of Things (IoT) applications.