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In a recently proposed indoor self-localization system, we excite dielectric resonators (DRs) in linear polarization (LP) as retrodirective passive tags, either as single DR, small array of DRs, or in combination with a spherical dielectric lens. DR tags mounted close to a reflecting wall suffer from large clutter return, which can supercede the DR tag signatures. To separate both into orthogonal polarizations, we design a polarization twist tag with two DRs tilted by ±45° and spaced by $\lambda $ /4. In the EM simulation and experiment, we show that this tag design allows efficient retrodirective scattering in cross polarization. The realized cross-polarization radar cross section (RCS) is equal to the scattering of a single DR in LP and 6 dB better than the RCS from a polarization splitting single DR with 45° tilt. This polarization signature is shown to allow separation of the DR signature from the high scattering level of a flat plate reflector placed behind the polarization twist DR tag. The potential of improving lens-DR combinations by using the polarization twist DR tag with circular polarization is also discussed. [ABSTRACT FROM AUTHOR]

For a novel indoor‐localization system, chipless tags with high retro‐directive radar cross‐section (RCS) under wide‐angle incidence are required as fixed landmarks. Tags based on dielectric resonators (DRs) were proposed to provide identification by resonance frequency coding. To achieve a satisfactory read range for the localization system, the low RCS levels of these tags require a major boost. A solution was found by adopting the metallic corner reflector which is known for high RCS levels over a wide bandwidth and over a wide angle of incidence. The study presents a novel corner reflector design where notches in the RCS spectral signature are created by the attachment of arrays of dielectric resonators to the metallic surfaces of corner reflectors. It is shown that notches appear due to the increased scattering of the resonators at resonance and by the power loss due to grating lobes formed in addition to the specular reflection from the arrays and from the metallic surfaces. Results from electromagnetic simulations are verified by measurements of an example dihedral corner reflector of 100 × 100 mm2 plate size with two arrays of 3 × 3 DRs producing a notch signature at about 7 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a realistic feasibility of radio frequency identification (RFID) based self-localization of objects in real environments using simple infrastructure composed of chipless tags. These tags are designed as arrays of dielectric resonators (DR) in order to overcome the range limitations of the traditional chipless tags, where the DR array structure of the tags boosts the radar cross section (RCS) and, consequentially, extends the range coverage. Furthermore, an efficient algorithm for tag detection is proposed considering the environmental and hardware impairments that alter the backscattered signal from the tag. In this system, the reader interrogates the reference nodes, i.e. chipless tags, by a frequency-sweep RF signal, and the backscattered signals from the tags are captured and analyzed at the reader for detection, ranging and location estimation. A testbed is implemented with fabricated chipless RFID tags in order to evaluate the validity and accuracy of the proposed self-localization system. Experimental measurements based simulations are conducted in several scenarios in order to evaluate the proposed system. Moreover, an object (the reader) is moved to several locations in an interrogation area of $2.5\times 1.2$ m, and, afterwards, its location is estimated. The averaged measured location error achieved based on the proposed system is approximately 5 cm with a variation of 0.9 cm as a minimum observed error and 7 cm as a maximum error. [ABSTRACT FROM AUTHOR]

In a novel mm-wave localization system, dielectric resonators (DR) have been proposed as passive chipless RFID tags to mark fixed reference nodes. To counter clutter and improve the limited read range due to the low RCS level of a DR at millimeter-wave frequencies we propose a combination of several DRs with a dielectric spherical lens which allows improvement of up to 30 dB. The paper presents the design principle and shows simulation results and experimental verification of a scaled tag operating in the 10–12 GHz range and covering a range of incidence angle of the reader signal of ± 50°. A frequency sweeping RF reader can identify the tag (information) by the peak of the RCS level at its DR resonant frequency. For a multiple-tag scenario we can realize up to 12 different tags which can be discriminated unambiguously by their resonant frequencies in a 1: 1.2 frequency bandwidth. [ABSTRACT FROM AUTHOR]

The RCS of flat cylindrical Dielectric Resonators (DR) is investigated and found to be too low for an application of the resonators as tags in a novel indoor localization system at mm-wave frequencies. As a method to increase the RCS of a DR tag, we propose the combination with a constant-index spherical lens. The collimation and scattering properties of this lens type are found suitable for a combination with DRs. The optimum relative permittivity of the lens is found in the range of ϵr=1.6 to 2.8 and the optimum distance between lens surface and DR is found slightly larger than the radius of the DR. RCS enhancement is found to vary with the modes of the DR but increases approximately with the fourth power of the lens radius. However, RCS signatures become corrupted by scattering due to mismatch effects of large lenses such that the lens diameter has to be limited to 4 to 5 wavelengths with the RCS enhancement limited to about 30 to 35 dB. Simulation and experimental verification are performed at a down-scaled frequency range from 4 GHz to 7 GHz using lenses of 60 mm and 120 mm diameter made of paraffin wax. [ABSTRACT FROM AUTHOR]

Passive chipless tags based on dielectric resonators (DRs) have been proposed for a novel millimeter-wave indoor self-localization system to mark fixed reference nodes. The tags employed in the system provide a unique spectral signature (resonance peaks) with much-increased radar cross section (RCS) by placing several identical DRs at the focal line of a spherical dielectric lens. Resonators of optimized geometry allow a modification of this original DR-lens tag by combining the lens with different size DRs which exhibit resonant frequencies separated by large frequency gaps. For easier manufacturing and testing, a demonstrator tag was designed for a “scaled” frequency range of 5–6 GHz with this configuration and is shown to produce spectral signatures of the monostatic RCS which are uniquely related to the angle of arrival (AoA) of the incident wave from a reader. Simulated signatures of a lens of 120-mm diameter with seven spherical DRs are presented and results are supported by experiment. Correlation processing of the signatures can give a resolution of few degrees in AoA while the bistatic RCS half-power beamwidth is on the order of 20°, and RCS levels of resonant peaks are produced between 0 and −6 dBm2. [ABSTRACT FROM AUTHOR]

Indoor localization based on unsynchronized, low-complexity, passive radio frequency identification (RFID) using the received signal strength indicator (RSSI) has a wide potential for a variety of internet of things (IoTs) applications due to their energy-harvesting capabilities and low complexity. However, conventional RSSI-based algorithms present inaccurate ranging, especially in indoor environments, mainly because of the multipath randomness effect. In this work, we propose RSSI-based localization with low-complexity, passive RFID infrastructure utilizing the potential benefits of large-scale MIMO technology operated in the millimeter-wave band, which offers channel hardening, in order to alleviate the effect of small-scale fading. Particularly, by investigating an indoor environment equipped with extremely simple dielectric resonator (DR) tags, we propose an efficient localization algorithm that enables a smart object equipped with large-scale MIMO exploiting the RSSI measurements obtained from the reference DR tags in order to improve the localization accuracy. In this context, we also derive Cramer–Rao lower bound of the proposed technique. Numerical results evidence the effectiveness of the proposed algorithms considering various arbitrary network topologies, and results are compared with an existing algorithm, where the proposed algorithms not only produce higher localization accuracy but also achieve a greater robustness against inaccuracies in channel modeling. [ABSTRACT FROM AUTHOR]