Filter-based slow wave structures for application in chipless microwave RFID

Abstract

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.

Higher order pulse modulators for time domain chipless RFID tags with increased information density

“…For the positioning of the modulators, the prototype exhibits wavelength scales. A prototype tag featuring the power divider modulator is realized independently and utilizes filter-based slow wave structures for a more compact tag design [7]. To maintain a reconfigurable phase, the stub line is repeatedly interrupted, as has already be shown in the circuit representation (Fig.…”

An ultra-wideband time domain reflectometry chipless RFID system with higher order modulation schemes

“…The delay on the tag is strongly limited when using TDR delay-linebased tags. As the propagation velocity on a tag is high and the dimensions and path length of the delay line should be as small as possible, typical delay values for TDR microwave tags are a few nanoseconds [7]. Therefore it is crucial to achieve a high bandwidth, which is generally limited either by regulatory constraints or reader hardware.…”

“…Microwave TDR tags can overcome this problem as tag dimensions are bigger and production tolerances are therefore not as critical as in SAW tags. Recent research on delay-line-based TDR tags focuses on reducing tag size by using structures such as filters [7] or left-handed delay lines [8]. These methods make it more difficult to implement higher order modulation schemes.…”

“…Higher order modulation schemes impose high demands on the reader. Many publications use vector network analyzers (VNA), as they provide high flexibility [7]. However, they are not suited for low-cost chipless RFID communication due to their high price.…”