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Hybrid Time-Frequency Coded Photonic Crystal-based Chipless Retroreflective Tag Landmarks

This paper studies the implementation of a hybrid time-frequency modulation scheme in the chipless retroreflective tag landmarks of a mm-Wave indoor self-localization system. The fully-passive implementation of the modulation scheme is demonstrated with high-Q cavities working at 78 GHz for frequency coding and different time delays induced by the length of the transmission line for time coding. Both modulations operate within the same bandwidth and are integrated in a monolithic dielectric slab using a Photonic Crystal (PhC) periodic structure. Three hybrid coded tag landmarks manufactured in Rogers 6010.2LM are evaluated in measurements at 60 cm. While the cavity response is distinctively traceable in frequency domain, time domain analysis shows that implemented delays are correctly read out by the reader with a discrepancy of less than 8 % compared with simulations, providing a proof of concept for hybrid time-freuuency coding in PhC-based tag landmarks.