Gridded Square-Ring Frequency Selective Surface for Angular-Stable Response on Chipless Indoor Location Tag Landmarks

This paper studies the use of gridded square-ring FSSs to encode the backscattered response of trihedral corner reflectors, acting as passive landmarks in a mm-wave indoor self localization system. Previous tags presented low resonance stability under oblique incidence of the incoming wave, which limits the system performance under real operating conditions. The designed FSS uses a miniaturized unit cell to minimize phase differences between its elements, which are responsible for the fluctuating resonance response. The smaller these phase differences, the less varies the response. The new design presents a more stable response than a previous work at W-band (65-110 GHz), at the cost of lower frequency selectivity and range. But, the operating angular region of the tag is ± 35°, which allows to encode 45 notches, which means 5.5 bits, under transverse magnetic planar wave excitation for identification of tags in indoor self-localizing applications.