A new concept for implementing delay elements in chipless TDR RFID tags is presented. It is based on filter design techniques and aims for less dispersive and compact designs. Since dispersion has influence on ISI and phase distortion, a reduction of the dispersion leads to an increase in the system's performance and the read range, respectively. This is first analyzed with the help of a system-theoretic simulation. From the filter design methods considered in this paper, the Butterworth method shows to be best suited for this purpose. An adaption of the Butterworth filter design regarding group delay design requirements is derived. A filter design is carried out and a delay section with low group delay dispersion is implemented. Finally, a prototype tag is realized and measured to verify the applicability of the designed filter-based slow wave structure for chipless TDR RFID tags.
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