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

Abstract

This paper introduces retroreflective lenses for millimeter-wave radio-frequency indoor localization. A three-dimensional (3D) gradient-index Luneburg lens is employed to increase radar cross section (RCS) of photonic-crystal high-Q resonators and its performance is compared to conventional radar retroreflectors. A classic Luneburg lens with and without a reflective layer is realized with 25 mm diameter (6.7 0), showing a realized gain of 24.6 dBi and a maximum RCS of-9.22 dBm 2 at 80 GHz. The proposed Luneburg lens with embedded high-Q resonators as frequency-coded particles in a photonic crystal structure, operating as a reflective layer, achieved a maximum RCS of-15.84 dBm 2 at the resonant frequency of 76.5 GHz and showed a repeatable response each 18° over ±36° in two perpendicular planes. With this high RCS of the Luneburg lens, a maximum readout range of 1.3 m could be achieved compared to 0.15 m without the lens at 76.5 GHz for the same transmit power, receiver sensitivity, and gain of the reader antenna.

Clutter Suppression for Indoor Self-Localization Systems by Iteratively Reweighted Low-Rank Plus Sparse Recovery

“…Previous works have combined corner reflectors as retro-reflective structures and dielectric resonators [ 6 ] or frequency selective surfaces [ 29 ] as coding particles, whereas others have used a combination of lenses for long-range reading with cavities implemented in electromagnetic band-gap structures as a combination of retro-reflective and coding parts [ 9 , 30 ]. The aforementioned tags have different operating principles and designs.…”

“…( d ) High-Q tag used in this paper. Combination of [ 30 , 31 ]. ( e ) Backscattered tags’ responses on the time domain.…”

Wide-Angle Ceramic Retroreflective Luneburg Lens Based on Quasi-Conformal Transformation Optics for Mm-Wave Indoor Localization

“…Moreover, frequency-coded corner reflectors are achieved by employing frequency selective surfaces [3]-- [4] or dielectric resonator arrays [5]- [7]. A large amount of retroreflective structures are based on lenses by incorporating a reflective layer, such as frequency-coded fused silica spherical lenses [8]- [9], or lenses backed by a photonic crystal (PhC)-based structures [10], such as a polyethylene lens with a Bragg grating [11], and planar [12] or spherical [13] gradient-index Luneburg lens backed by planar PhCs. Finally, the Luneburg lens can also be employed to achieve an omnidirectional retroreflector when it is surrounded by slant polarizers [14].…”

“…Most of the aforementioned references comprise frequency coding, enabling their employment in different areas. For instance, in chipless indoor selflocalization systems [3], the ability to distinguish between retroreflectors inside the building allows for a precise position calculation, which is achieved by incorporating different and distinguishable frequency-coded signatures to the reflected wave of each retroreflector [3]- [13]. The advances in those researches bring unconventional retroreflectors based on metasurfaces [15]- [18], or on transformation-optics (TO) principles [19]- [23].…”

“…The use of retroreflectors at mm-wave frequencies allows for wider absolute bandwidths, i.e., a better ranging accuracy and smaller devices, as well as higher antenna gains [6]. More details can be found in our previous work [13], where a combination of a spherical 3D Luneburg lens with 2D PhC coding particles is introduced at 80 GHz. Further, in [24], we addressed the current limitations of a lens-based system due to limited angular response and overall reduced compactness of the coding particles, i.e., having to adapt the employed planar coding particles (2D PhC, resonating element arrays) to the spherical surface of a lens introduces undesired effects.…”