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

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.