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

Abstract

This paper introduces three novel passive phase modulators for entirely electromagnetic chipless time domain RFID tags. The modulators overcome limitations of earlier approaches and allow for a highly increased signal space coverage, and, therefore, the implementation of high order PSK or QAM schemes. All three modulators are studied in theory and practically implemented up to a 16-PSK on a reconfigurable prototype tag with 4 modulation stages, realizing a 16 bit information content. Besides showing the measurement results, the assets and drawbacks of the three approaches are carefully compared and the achieved information density is related with approaches from literature.

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

“…The chipless TDR RFID tag is presented in [10] and is based on a meandered transmission line on a Rogers RT/duroid ® 6006 substrate. The meandered line is interrupted by modulation sections where stub line or impedance step modulators are placed.…”

“…Multiple reflections that result from the stub lines and impedance steps cannot be suppressed by the calibration. Higher order modulation schemes can be realized as shown in [10]. A 16-PSK has been implemented successfully and measured with a VNA.…”

“…Reader and tag are matched to deliver an improved SNR, a feature needed for higher order modulations. We used an 8-PSK-and-2-PPM combination for the wireless measurements in order to achieve the same 16-bit information content proposed in [10]. We conducted tests in an anechoic chamber.…”

“…Afterwards the reflectors are placed on the tag. As stub-line-based modulators provide the best results in [10], they are employed here as well. Different codes were tested with a single tag at a distance of 50 cm to the reader antennas.…”

“…Another approach constructing a delay-line-based TDR tag are meandered transmissions lines [9]. A 16-PSK has been successfully implemented in such an RFID tag [10]. Higher order modulation schemes impose high demands on the reader.…”