Frequency-Coded Spherical Retroreflector for Wide-Angle Indoor Localization Tag Landmarks

This paper studies the suitability of frequency-coded spherical retroreflectors as passive tag landmarks in a mmwave indoor self-localization system. By designing a spherical tag as a combination of two simple structures, spherical retroreflectors with frequency selective surfaces, wide readout angles are expected, while keeping manufacturing complexity low. The fabricated tag presents successful frequency coding at 82 GHz in an angular range of 120°, with a measured average radar-cross section of -15 dBsqm in that range. Moreover, the tag works for both transverse electric and transverse magnetic plane waves and has an operating bandwidth of 6.1%, allowing for the encoding of 9 notches, or 3.17 bits, in W-band.