Gérard Chassay

A deterministic ultra wideband channel modeling

We study the realisation of a deterministic channel modeling which allows the construction of a realistic received waveform from a wireless spread spectrum multiple-access (SSMA) using time hopping (TH) modulation. The goal is to reach the symbol decision from a simulated waveform. This paper explains how to use the uniform theory of diffraction (UTD) method combined with a ray tracing to obtain the received TH modulation waveform in indoor or outdoor environment.

A STUDY OF THE DESYING PROCESS OF A RADAR TARGET APPLIED TO A CRITICAL ANALYSIS OF THE MEANING AND THE SENSIBILITY OF SOME MEASURED HUYNEN PARAMETERS

We analyze the polarimetric behavior of some targets. This leads to an instability and to the loss of meaning for the Huynen parameters, which are used for the analysis of radar images. We then propose a new method for the treatment of the corresponding uncertainty in the desying process, which leads to a physical choice of the correct set of Huynen parameters. Some measurement results are then given.

UWB Radio Link Modeling for Multipath Environment

Ultra-wideband (UWB) systems have the potential to provide very high data rates over short distances. This paper details the construction of the received signal from a pulse waveform on the transmission line at the transmitter to the received signal at the receiver allowing a fine analysis of antennas impact on UWB systems. This is used for deterministic modeling based on ray tracing (RT) and geometrical optics (GO). The paper presents the way of sizing the pulse amplitude in order to satisfy a given power spectral density (PSD) mask for a given modulation. The proposed approach is demonstrated to be coherent with classical power link budget.

Prediction of the over-sea electromagnetic wave propagation by a novel PE-MoM hybrid technique

A new method for studying electromagnetic wave propagation through a discrete random medium over the sea surface is described. This technique uses a parabolic equation code for the over sea propagation and a method of moment code for the propagation through the medium. The hybridisation is based on the decomposition of the output field of the PE code as a weighted sum of plane waves.

Modelling of ultrawideband echoes from rough dielectric surfaces by calculating physical optics currents

This paper presents anew method for the deterministic prediction of UWB radar clutter. It is based on a physical optics approach combined with a discrete Fourier transform. Results for different kinds of realistic measurement situations are presented.

Modeling shadow region due to propagation through discrete random media

Because of the development of cellular systems, the prediction of the propagation through discrete random media appears to be very useful. Recent works have shown the existence of a region with additional attenuation to that caused by free-space propagation. This paper aims at approaching the main phenomena responsible for this attenuation with an analytic formulation. The results are essentially based on the resolution of the problem of diffraction by thin-wire structures with the method of moments (MoM).

Analyse de l’influence des phénomènes de dépolarisation des ondes radar sur les images ROS polarimétriques

This paper first analyses the evolution of the polarisation state of electromagnetic waves propagating through any medium. This is done by a novel formalism which is based on the characteristic polarisations concept. This formalism is then generalised to the up and down path,i.e. to radar systems. This study is then applied to the tropospheric and the ionospheric media, which are involved insar (synthetic aperture radar) imaging. Finally, we focus on their influence on the value of some polarimetric tools, which have been shown to be useful insar images analysis.RésuméCet article analyse dans un premier temps l’évolution de l’état de polarisation d’une onde traversant un milieu quelconque. Un formalisme basé sur la notion de polarisation caractéristique est ensuite proposé puis étendu au cas d’un système radar, c’est- à -dire au cas d’une propagation aller puis retour. Cette étude théorique est alors appliquée à l’étude des milieux troposphérique et ionosphérique impliqués dans l’imagerieros (radar à ouverture synthétique), et plus précisément à l’évaluation de l’influence qu’ils peuvent avoir sur la valeur de différents paramètres d’analyse polarimétrique des images.Cet article analyse dans un premier temps l’evolution de l’etat de polarisation d’une onde traversant un milieu quelconque. Un formalisme base sur la notion de polarisation caracteristique est ensuite propose puis etendu au cas d’un systeme radar, c’est- a -dire au cas d’une propagation aller puis retour. Cette etude theorique est alors appliquee a l’etude des milieux tropospherique et ionospherique impliques dans l’imagerieros (radar a ouverture synthetique), et plus precisement a l’evaluation de l’influence qu’ils peuvent avoir sur la valeur de differents parametres d’analyse polarimetrique des images.

A new time domain and polarimetric measurement algorithm for complex target reconstruction

With the aim of a practical validation of theoretical models, software was developed using the high-frequency-domain assumption. This permits one to construct a database of polarimetric behavior for a large number of saddle points such as dipole, infinite half-plane, tip, edge, wedge, surface wave, progressive wave, cylinder, sphere, concave surface, dihedral, trihedral, and plane surface. The inverse problem in which it becomes possible with a simple measurement of the scattering matrix to recognize the target shape is presented. All the measurements are made using a vector network analyzer with a time-domain option. With a selective time acquisition and analysis of the main saddle points of the target, information concerning distance and polarimetric behavior can be obtained. By comparison, with data calculated previously for elementary saddle points, most realistic objects can be determined. Good agreement between experimental measurements and predicted ones is observed in the X band (8-13 GHz).<<ETX>>

Complex target polarimetric modelization and measurement

A numerical algorithm for the modeling of the polarimetric effects from a large number of isolated saddle points is presented. The association of these points gives a good estimation of the polarimetric effects of complex target shapes. It also permits the modeling of a group of saddle points attached or not attached to the same target. Moreover, it can predict the polarimetric signatures of any object in the presence of a clutter medium such as chaff, disks, and spheres. Good agreement between theoretical results and experimental measurements is observed.<<ETX>>