Design and Measurements of a Quasi-isotropic UWB Planar Antenna

ISSN 1874-4761This paper summarizes the design and measurements of a quasi-isotropic printed UWB antenna, with the analysis of its performances through defined figures of merit. State of the art and review of some recent patents give us the opportunity to exploit some empirical considerations about the shape and the methodology of conception. A simple structure is simulated by means of CST Microwave Studio to show the possibility of fulfilling, at a defined level, UWB antenna requirements such as matching, fidelity and quasi-isotropy of the radiation pattern with a simple micro-strip design and a standard technology. The design of this antenna is based on considerations about bulbous and bended traveling wave antennas. Results of its characterization in anechoic chamber are quantified in terms of amplitude and phase variation, in order to illustrate the level of dispersion for the different directions. The article presents some promising patents on quasi-isotropic UWB antenna

Robust antenna diagnostics method using equivalent elemental dipoles and the spherical wave expansion

International audienceA robust method for antenna diagnostics that can provide the reconstruction of the aperture field from spherical near- or far-field measurements, is presented. This method is based on the equivalence principle which consists in the rewriting of the spherical wave expansion of the radiated field in terms of infinitesimal electric and magnetic dipoles distributed over the antenna main surface. This method presents the advantage of being very stable and extremely robust beside the measurement noise. Synthesized data (simulated antenna) used with different level of noise will show the viability of this technique for antenna diagnostics purpose

A New Criterion to Jointly Design the Antenna and Optimize the Communication Capacity in IR-UWB.

International audienceThis paper presents the impact of the antenna design over the capacity of a IR-UWB system in a Multi-User Interference environment. A new antenna design is proposed and it is showed using a new performance criterion that for this design, the communication capacity given by the Sholtz's pulse [13] might be reached using some other types of pulses

Numerical and experimental assessment of a phase retrieval technique applied to planar near field distribution for wide band application

International audienceThe work presented in the following is devoted to the characterization of an harmonic source in a wide band of frequencies [0.5, 20 GHz] from the knowledge of the amplitude-only electric fields at near field measurement distance. Such a problem leads to the development of a “phase reconstruction” algorithm. In that paper a classical propagation/retro-propagation scheme has been applied. This is the first step of a study concerning the characterization of electromagnetic pulsed source from phaseless measurement techniques in near field conditions. The algorithm has been tested and validated using numerical and experimental data acquired at different frequencies and in different configurations

The use of infinitesimal dipoles and the spherical wave expansion for planar antennas modeling

International audienceIn this paper, a method to derive an equivalent radiation model for planar antennas is presented. This method uses the spherical near-field (NF) data (measured or computed) to ascertain an equivalent set of infinitesimal dipoles placed over the main antenna surface. The spherical wave expansion (SWE) of the NF data is written in terms of infinitesimal dipoles using a transition matrix. This matrix expresses the linear relations between the spherical wave coefficients of the antenna and the spherical wave coefficients of each dipole. Once the excitation of each dipole is known, the field at any angle and distance from the antenna is rapidly calculated even inside the minimum sphere. Computations with EM simulation data of an antenna array illustrate the reliability of the method

Aperture antenna modelling by a finite number of elemental dipoles from truncated spherical field measurement: Experimental investigation

International audienceA method to determine a distribution of a finite number of elementary dipoles that reproduce the radiation behaviour of the antenna under test (AUT) from truncated spherical field measurements is proposed. It is based on the substitution of the actual antenna by a finite number of equivalent infinitesimal dipoles (electric and magnetic), distributed over the antenna aperture. This equivalent set of elementary dipoles is optimized using the transmission coefficient involving the spherical wave expansion of the measured field and using an appropriate matching method. Once the current excitation of each dipole is known, the radiated field of the antenna at different distances can be rapidly determined. The reliability and the accuracy of the method are shown using experimental data issued from the measurement of an X-band horn antenna, in two different measurement setups

Vers des écosystèmes d'objets sociaux

International audienceLe concept d'objet social est structurant pour le web à l'heure où le découplage entre plateformes de contenus et plateformes sociales s'accentue. Nous étudions dans cet article la notion d'objet social au travers d'un faisceau d'évolutions technologiques qui lui sont favorables. Premièrement les technologies du web sémantique et leur application au web social suscitent l'intérêt grandissant des acteurs du web. Deuxièmement l'avènement de la vision de l'informatique ubiquitaire réduit l'écart entre les sphères numériques et physiques et impacte les interactions sociales. Dans ce contexte porteur nous proposons une représentation du concept d'objet social et des structures de communications afférentes en vue d'une communication plus efficace. Ce travail débouche sur l'ontologie OCSO présentée dans cet article

Pervasive sociality: advanced social objects recommendation

International audienceThis paper makes a focus on social objects and stresses the importance of object-centered sociality in emerging technological context. Actual digital object centered sociality limits and related challenges are reviewed. We propose to foster social interactions through advanced social objects recommendations. In this context the Object Centered Sociality Ontology (OCSO) is presented. The paper concludes with research perspectives and a promising approach for social object recommendation through spreading activation algorithm

Experimental compaction of anisotropic granular media

We report on experiments to measure the temporal and spatial evolution of packing arrangements of anisotropic and weakly confined granular material, using high-resolution $\gamma$-ray adsorption. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical solicitations evolve to a dense state. We find that the packing fraction evolution is slowed by the grain anisotropy but, as for spherically shaped grains, can be well fitted by a stretched exponential. For a given type of grains, the characteristic times of relaxation and of convection are found to be of the same order of magnitude. On the contrary compaction mechanisms in the media strongly depend on the grain anisotropy.Comment: to appear in the european physical journal E (EPJE

Discovery Hub: on-the-fly linked data exploratory search

International audienceExploratory search systems help users learn or investigate a topic. The richness of the linked open data can be used to assist this task. We present a method that selects and ranks linked data resources that are semantically related to the user's interest. The objective is to focus the user's attention on a meaningful subset of highly informative resources. We extended spreading activation to typed graphs and coupled it with a graph sampling technique. The results selection and ranking is performed on-the-fly and doesn't require pre-processing. This allows addressing remote SPARQL endpoints. We describe first implementation on top of DBpedia. It is used by the Discovery Hub exploratory search system to select interesting resources, to support faceted browsing of the results, to provide explanations and to offer redirections to third-party services. Results of a user evaluation conclude the article