Phaseless computational imaging with a radiating metasurface

Computational imaging modalities support a simplification of the active architectures required in an imaging system and these approaches have been validated across the electromagnetic spectrum. Recent implementations have utilized pseudo-orthogonal radiation patterns to illuminate an object of interest---notably, frequency-diverse metasurfaces have been exploited as fast and low-cost alternative to conventional coherent imaging systems. However, accurately measuring the complex-valued signals in the frequency domain can be burdensome, particularly for sub-centimeter wavelengths. Here, computational imaging is studied under the relaxed constraint of intensity-only measurements. A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval. In this paper, the methodology associated with this novel principle is described, studied, and experimentally demonstrated in the microwave range. A comparison of the estimated images from both complex valued and phaseless measurements are presented, verifying the fidelity of phaseless computational imaging.Comment: 18 pages, 18 figures, articl

Computational polarimetric microwave imaging

We propose a polarimetric microwave imaging technique that exploits recent advances in computational imaging. We utilize a frequency-diverse cavity-backed metasurface, allowing us to demonstrate high-resolution polarimetric imaging using a single transceiver and frequency sweep over the operational microwave bandwidth. The frequency-diverse metasurface imager greatly simplifies the system architecture compared with active arrays and other conventional microwave imaging approaches. We further develop the theoretical framework for computational polarimetric imaging and validate the approach experimentally using a multi-modal leaky cavity. The scalar approximation for the interaction between the radiated waves and the target---often applied in microwave computational imaging schemes---is thus extended to retrieve the susceptibility tensors, and hence providing additional information about the targets. Computational polarimetry has relevance for existing systems in the field that extract polarimetric imagery, and particular for ground observation. A growing number of short-range microwave imaging applications can also notably benefit from computational polarimetry, particularly for imaging objects that are difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure

Imagerie MIMO ULB à haute résolution par un composant passif à port unique

National audienceUne technique de compression permettant l'acquisi-tion d'images RADAR 3D à haute résolution est présen-tée dans cet article. Basée sur un principe d'acquisition comprimée, les informations reçues par un réseau d'an-tennes MIMO ULB sont mesurées sur un port unique. Après reconstruction des formes d'ondes reçues en post-processing, il est alors possible de réaliser des images 3D de façon rapide grâce aux développements récents en terme d'algorithmes MIMO

Experimental implementation of an Ultra-Wide Band MIMO radar

International audienceIn this paper, a radar system implementation isaddressed to detect a point target, that is a Multiple-InputMultiple-Output (MIMO) Radar. It is an emergent concept inradar field and has reached a substantial considerations. Theadvantages of MIMO radars is presented in comparison of SIMOand SAR radars. The simulation and measurement results showthat the MIMO Radars can reach a better angular resolutionwhile keeping a small number of antennas

Mise en oeuvre expérimentale d’un Radar MIMO Ultra-Large Bande

International audienceCe document présente la mise en oeuvre expérimentale d'un Radar MIMO ULB pour la détection de cibles ponc-tuelles. L'avantage du radar MIMO revient à améliorer la résolution angulaire sans avoir à augmenter le nombre d'antennes nécessaire dans les radars conventionnels et ce, grâce à la création d'un réseau d'antennes virtuelles plus large que le réseau physique. Les résultats obtenus en simulation et en mesure sont également comparés aux systèmes Radar classiques à balayage de faisceau (SIMO) et à ouverture synthétique (SAR)

Experimental Synthetic Aperture Radar with Dynamic Metasurfaces

We investigate the use of a dynamic metasurface as the transmitting antenna for a synthetic aperture radar (SAR) imaging system. The dynamic metasurface consists of a one-dimensional microstrip waveguide with complementary electric resonator (cELC) elements patterned into the upper conductor. Integrated into each of the cELCs are two diodes that can be used to shift each cELC resonance out of band with an applied voltage. The aperture is designed to operate at K band frequencies (17.5 to 20.3 GHz), with a bandwidth of 2.8 GHz. We experimentally demonstrate imaging with a fabricated metasurface aperture using existing SAR modalities, showing image quality comparable to traditional antennas. The agility of this aperture allows it to operate in spotlight and stripmap SAR modes, as well as in a third modality inspired by computational imaging strategies. We describe its operation in detail, demonstrate high-quality imaging in both 2D and 3D, and examine various trade-offs governing the integration of dynamic metasurfaces in future SAR imaging platforms

Passive UWB Beamforming: a N to M Compression Study

International audience—Recent works have demonstrated the feasibility of microwave imaging using compressive techniques, exempting the use the of active delay lines, phase shifters, or moving parts to achieve beamforming. With this method, waves are coded in a passive way by a compressive device to reduce the complexity of the transmitter and/or receiver chains of the telecommunication and radar systems requiring beamsteering. Since this technique is based on frequency diversity, the reduction of the compressive device's volume imposes a diminution of the amount of driven antennas. In this article, the improvement brought by simultaneous excitations of the compressive device is presented. Adapting a new mathematical formulation, it is shown that M inputs can send independent waveforms allowing the beamsteering of an N-elements antenna array, while maintaining N > M

Algorithme de projection pour l’imagerie microonde à haute résolution en temps réel

National audienceUne technique de calcul de projection 2D d'images radar est présentée dans cet article. Dans de nombreux cas tels que les scanners d'aéroport, une projection d'image 3D est suffisante pour détecter les éléments visés et ap-porte plus d'informations qu'une simple coupe 2D, no-tamment lorsque la distance de l'objet n'est pas connue précisément. En réalisant une projection des voxels à re-construire sur un plan, il est possible de diminuer le temps de calcul et la mémoire nécessaires à l'obtention des images. Le principe théorique de cette méthode est dé-veloppé dans ce papier suivi de résultats issus de simulations. Enfin, les gains apportés en termes de temps de calcul sont présentés

Computational Microwave Imaging Using 3D Printed Conductive Polymer Frequency-Diverse Metasurface Antennas

A frequency-diverse computational imaging system synthesized using three-dimensional (3D) printed frequency-diverse metasurface antennas is demonstrated. The 3D fabrication of the antennas is achieved using a combination of PolyLactic Acid (PLA) polymer material and conductive polymer material (Electrifi), circumventing the requirement for expensive and time-consuming conventional fabrication techniques, such as machine milling, photolithography and laser-etching. Using the 3D printed frequency- diverse metasurface antennas, a composite aperture is designed and simulated for imaging in the K-band frequency regime (17.5-26.5 GHz). The frequency-diverse system is capable of imaging by means of a simple frequency-sweep in an-all electronic manner, avoiding mechanical scanning and active circuit components. Using the synthesized system, microwave imaging of objects is achieved at the diffraction limit. It is also demonstrated that the conductivity of the Electrifi polymer material significantly affects the performance of the 3D printed antennas and therefore is a critical factor governing the fidelity of the reconstructed images.Comment: Original manuscript as submitted to IET Microwaves, Antennas & Propagation (2017). 17 pages, 8 figure