Trimmed Aperture Corner Reflector for Angle-Selective Chipless RFID

This letter presents trimmed aperture corner reflectors (CRs) for assigning angle selectivity to chipless radio frequency identification (RFID) tags. This angle selectivity can benefit the landmark use of CR-based tags by exhibiting different signals in each direction, which enables infrastructure-to-device communication with rich context. The key idea of this work is to subtract retroreflections in unwanted directions by partially trimming the aperture of CRs, allowing control over the radar crosssection (RCS) when looked at from different angles. We developed a geometric analysis based on the effective area of CRs to determine the appropriate aperture trimming for the desired angular characteristics. This method can append direction selectivity to various CR-based chipless RFID tags. We demonstrate a trimmed CR-based spatially coded chipless RFID that can present different 4-bit IDs in three different directions while maintaining a large RCS of 1.80 dBsm. The proposed method can artificially code the selective reflections in passive reflectors and is suitable for the applications requiring large detectability, such as outdoor landmarks and signs.