IR-UWB Reader for Credit Card-Sized NFC Chipless RFID Tag using Asymmetrical Stepped Impedance Resonators

In this paper, an impulse radio ultra-wideband (IR-UWB) reader is proposed for a credit card-sized near field communication (NFC) chipless radio frequency identification (RFID) tag based on asymmetrical stepped impedance resonators (SIRs). We have succeeded in generating a stable waveform using a high-speed digital circuit to generate ultrashort pulses for reducing the sampling jitters of receiver. In addition, Direct Digital Synthesis (DDS) is used to generate a difference of 25.833 Hz between the transmit pulse frequency and the received pulse frequency to generate accurate sampling timing. By acquiring a waveform at an equivalent sampling frequency of 1,261.393 GHz, a dynamic range for the reader of 70 dB or more is obtained and reducing noise by narrowing the intermediate frequency (IF). We also experimentally confirmed that the proposed reader can measure the resonance frequencies of the SIR for chipless RFID tags in the frequency ranging from 0.4 GHz to 6 GHz within 0.66 % normalized frequency error.