Mathematical Model of Chipless RFID Tags for Detection Improvement

A mathematical model to characterize a frequency-coded chipless radio frequency identification (RFID) is presented. A chipless tag is comprised of multiple high-quality factor resonators. The model exploits the bandpass and band-stop characteristics of a frequency-coded tag and the channel model of the reader and tag system. The proposed model accurately reconstructs the time and frequency responses of the tag read by a reader antenna. The model is universal to any type of chipless tag. To validate the model, first, a tag is designed with CST Microwave Studio, a full-wave electromagnetic solver, and its resonant characteristic is extracted. The model is used to validate the simulation and measurement results of the same tag. Also, the tag is measured in a cluttered environment. The results show that the tag is successfully decoded in the presence of a relatively large metallic reflector to verify the robustness of the model, without any calibration. The investigation provides a comprehensive understanding of the tag and the reader system, and it is a step toward reading a chipless tag in a realistic environment.