Frequency Selective Surface Coded Retroreflectors for Chipless Indoor Localization Tag Landmarks

Abstract

This letter presents the integration of frequency selective surfaces (FSSs) with retroreflectors for the realization of chipless wireless indoor localization tag landmarks. As an example, the high radar cross section (RCS) of a trihedral corner reflector is signed with an FSS-based stopband filter, so that the backscattered power from several corner reflectors can be distinguished by a mobile reader according to the frequency response of the FSS. Measurement results with a 3 × 3 × 3 cm 3 trihedral corner reflector and a stopband FSS in a Rogers RT/Duroid 5880 high-frequency laminate at 90 GHz shows an RCS above −25 dBsqm for 90°c overage in the TM plane. Due to the high RCS, measurements at distances up to 4 m with a standard 25 dBi gain horn antenna and a vector network analyzer as a reader are shown. These preliminary results show the potential of the concept for applications such as indoor localization with sub-mm accuracy, where high bandwidths, but only a low number of bits, are needed for the identification of the tag landmarks.

Gradient-Index-Based Frequency-Coded Retroreflective Lenses for mm-Wave Indoor Localization

“…From the previous comparison, it can be concluded that the highest RCS is achieved by the trihedral cubical corner reflector. Coding in corner reflectors can be achieved by frequency selective surfaces [6], dielectric resonators [7], or thin film modulators [8] with high RCS for applications such as indoor localization. Similarly, coding in flat plate reflectors can be achieved by a frequency selective surface plate, a planar dielectric resonator array in front of a metal plate [9], or microstrip coding [10], but this type of reflectors share the abrupt RCS decay for directions other than broadside of the flat metal reflector.…”

“…where r denotes the relative permittivity and R is the radius of the lens. The monostatic RCS of the retroreflective Luneburg lens at the boresight can be calculated by equation (6).…”

“…Such retroreflectors can become smaller with the wavelength, while the accuracy of radar ranging algorithms increases at higher frequencies due to the higher absolute bandwidth [5]. For these reasons, the realization of retroreflectors in the mm-wave (30 GHz to 300 GHz) frequency range has received increasing attention [6][7], [9][10][11][12][13]. For successful localization, the reader must identify each retroreflector to find their position in the database.…”

“…In an indoor self-localization environment, passive methods are advantageous due to the absence of a battery, i.e., no maintenance needed. A simple solution is the realization of mm-wave retroreflectors to generate one or several notches in an otherwise frequency-stable backscattering response of trihedral corner reflectors [6,7,9,11]. Despite their high RCS, the identification of passive retroreflectors can be unstable due to strong reflections in the nearby environment, i.e., clutter, such as naturally occurring OLUME XX, 2017 1…”

Frequency-Coded mm-Wave Tags for Self-Localization System Using Dielectric Resonators

“…A simpler and very efficient alternative to the above corner reflector design was found by adopting a concept [25], first demonstrated using a stopband frequency selective surface (FSS) based on conductor patterns (crossed dipoles) as depicted in Fig. 5.…”