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Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An extended utd (eutd) solution is developed for the scattering and diffraction of high frequency em fields from higher order (polynomial and spline defined) curved surfaces. The new solution is computationally efficient and overcomes the difficulties of the classic go/gtd/utd solutions near ray caustics and caustic terminations. The approach for constructing the eutd solution is based on a spatial domain radiation integral representation for the scattered field which is then reduced using a uniform asymptotic procedure. Further heuristic modifications are also made and correct the go induced current assumption near the shadow boundaries. New uniform reflection, first order edge diffraction, and zero-curvature diffraction coefficients are then derived and involve higher order phase integrals as canonical functions. Numerical results involving third and fourth order polynomial strips are provided and compare favorably with reference moment method results. abs]Fr|Résumé Une théorie uniforme de la diffraction étendue (eutd) est développée pour la diffraction ď un champ électromagnétique à haute fréquence sur des surfaces de courbure complexe. La nouvelle résolution est intéressante du point de vue du temps de calcul et permet ď éviter les difficultés classiques des méthodes gtd/utd près de certaines caustiques. ľ approche prise pour la construction de ľ eutd est basée sur une représentation intégrate dans le domaine spatial du champ diffracté, réduite par une procédure asymptotique uniforme. Des modifications heuristiques sont faites qui corrigent le courant ď optique géométrique près de la frontière ď ombre. Des expressions uniformes sont alors déduites qui demandent le calcul ď intégrates de termes possédant une phase ď ordre élevé. Des résultats numériques sont donnés et comparés avec ceux obtenus par une méthode des moments. [ABSTRACT FROM AUTHOR]

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pour étudier la diffraction d'une onde électromagnétique monochromatique par une cible radar de forme complexe, on modélise souvent l'objectif par un ensemble de points brillants. Bien que la majorité des points brillants soit associée aux zones de réflexion spéculaire sur l'objectif la section efficace de rétrodiffusion ( ser) dépend également des discontinuités de surface de la cible. Cet article présente une méthode qui permet de modéliser les discontinuités par des ensembles de points brillants dont les positions et les ser sont calculées. Bien que les ser soient généralement des fonctions décroissantes de la fréquence, que l'on peut parfois négliger, il est montré qu'il existe des cas relativement fréquents où elles deviennent indépendantes de la longueur d'onde. Des formules générales sont établies. L'accent est mis sur l'utilisation possible de l'intégrale de l'optique physique, dont les hypothèses de validité ne sont pas respectées, à condition d'introduire un nombre, variable suivant les cas, de coefficients correcteurs incluant les polarisations, dont les expressions sont précisées. L'évaluation des ser en est simplifiée et il y a unicité de méthode pour le traitement des zones de réflexion spéculaire et des discontinuités de surface. In order to study the scattering of a monochromatic electromagnetic wave by a complex radar target, specialists usually modelize the target by a discrete scatterers model. The majority of the scatterers are represented by specular points of reflexion on the surface of the target, but the radar cross section ( rcs) is also a function of surface discontinuities. In this article, we develop a method which allows us to replace the discontinuities by groups of point contributors of which the positions and the rcs are given. Eventhough the rcs are generally functions which decrease as the frequency increases, which can at times be neglected, it can be shown there exists quite frequently rcs which are independent of the wavelength. General formulae are given. It is emphasized that the physical optic integral may be used to calculate rcs eventhough the conditions of application are not correct. For this reason a number of coefficients including the polarisations are used. The formulae of these coefficients are given. As a result an evaluation of the rcs may be simplified, and the same method may be used to study the specular regions and the surface discontinuities. [ABSTRACT FROM AUTHOR]

Cette étude présente la diffraction d'ondes électromagnétiques impulsionnelles par des structures filaires minces de forme quelconque situées au-dessus d'un sol caractérisé par une conductivité σ. Le problème dont l'étape essentielle est la détermination du courant induit sur le fil est résolu à partir d'équations intégrodijférentielles établies directement dans le domaine espace-temps en tenant compte de la présence du sol réel. Des applications sont choisies dans le domaine de la protection d'installations de télécommunications et du réseau EDF ou SNCF contre les impulsions électromagnétiques parasites. This paper shows the scattering of electromagnetic pulses by thin wire structures of any form, above a homogeneous ground characterized by a conductivity a. The problem from which the capital stage is the determination cf the current induced on the wire, is resolved by integral equations, directly established in spacetime domain, taking into account the presence of the earth. Some applications are chosen in the protection domain of telecommunications equipments and electric or railway systems. [ABSTRACT FROM AUTHOR]

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

L'utilisation des équations intégrales en régime temporel permet dans beaucoup de cas de calculer la diffraction et la pénétration du champ électromagnétique par des schémas itératifs explicites. On étudie le cas des surfaces conductrices, des conducteurs minces, des ouvertures et des blindages de conductivité finie sous l'angle de la simplicité des équations et de leur domaine de validité. Les exemples d'application concernent le rayonnement d'un doublet lointain tombant sur un cylindre fermé, ou percé d'une ouverture, ou imparfaitement conducteur. It is possible in many cases by using space-time integral equations to compute the scattering and penetration of electromagnetic fields via explicit time-stepping diagrams. The case of conducting surfaces, thin scatterers, apertures and shieldings of finite conductivity are discussed with emphasis on the simplicity and the validity domain of the relevant equations. Examples concern the field of a far-located dipole incident on a cylinder with infinite conductivity, with an aperture or with resistive walls. [ABSTRACT FROM AUTHOR]

L'auteur suppose que l'émission électromagnétique de l'éclair des ondes métriques et décimétriques est due à la phase d'arc transitoire dans le mécanisme d'ionisation de l'air vierge. Un calcul du champ rayonné par la formation d'un plasma dans l'air à la pression atmosphérique est comparé aux résultats expérimentaux obtenus sur l'éclair réel. La très bonne concordance des résultats nous permet de supposer que les mécanismes d'arc transitoire sont responsables de l'émission de l'éclair. The author assumes that the electromagnetic radiation in the VHF-UHF range associated with lightning is due to the transient arc phase in virgin air ionization process. Theoretical calculation of electromagnetic radiation of plasma formation in the air at atmospheric pressure is compared to experimental results on lightning. The close correlation between these results leads to associate vhf-uhf radiation of lightning to the transient arc phase. [ABSTRACT FROM AUTHOR]

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pour étudier le phénomène de diffraction d'une onde électromagnétique monochromatique par un objectif de forme complexe (généralement un avion), les spécialistes en techniques radar, ont coutume de modéliser la cible par un ensemble de sources ponctuelles indépendantes. Le modèle obtenu est appelé modèle des points brillants en raison de l'identification de la majorité des sources avec les points de réflexion spéculaire à la surface de la cible. La possibilité de détermination optique des points spéculaires [1] et la simplicité apparente du modèle rendent la méthode très attrayante, ce qui explique son succès. Les ouvrages qui traitent de cette modélisation accordent généralement peu d'importance à la justification de la méthode et la supposent acquise a priori. Il en résulte parfois une impression d'empirisme et une assimilation trop hâtive du problème électromagnétique au problème optique équivalent, ce qui conduit à des résultats décevants ou inutilisables pour des cibles même très simples. Dans cet article l'auteur s'attache à préciser la notion de point brillant spéculaire et montre que les frontières d'ombre à la surface d'un objectif, sont également représentables par des points brillants virtuels, ce qui permet de les inclure simplement dans le modèle. Il étudie l'influence de ces points virtuels sur la section efficace de rétrodiffusion des cibles et illustre les résultats obtenus en appliquant la méthode à quelques objets simples. In order to study the scattering of a monochromatic electromagnetic wave by a complex target (generally a plane), radar specialists usually replace the target by a collection of independent point contributors. The model obtained is called a discrete scatterers model because the majority of the scatterers are represented by specular points of reflection on the surface of the target. The possibility of optical perception of specular points and the apparent simplicity of the method make it very attractive, and this explains its success. The litterature about this technique tends to assume that it is known and understood, and therefore rarely explains the basics. The result is sometimes an impression of empiricism and a tendancy to mistake the optical problem for the easily ignored electromagnetic one which often leads to results so bad that they cannot be used even for the simplest of targets. In this article, the author explains the concept of point contributor in detail and show that the shadow boundaries on the surface of a target can also be represented by imaginary specular points and thus can be easily included in the model. The author studies the effect of imaginary points on the radar cross section of the targets, and illustrates the results obtained by applying the method to a few simple objects. [ABSTRACT FROM AUTHOR]

La diffraction en régime transitoire est traitée directement dans le domaine temporel par une méthode originale utilisant la théorie des distributions. Pour les obstacles métalliques parfaitement conducteurs, cette approche généralise les solutions existantes dans la littérature, mais permet aussi d'établir de nouvelles équations intégrales donnant la solution des problèmes de diffraction à deux dimensions (l'onde et l'obstacle présentent une symétrie de translation ou de révolution). Des applications dans le domaine de la protection d'installations de télécommunications contre les impulsions Em ( foudre, impulsion Em d'origine nucléaire, etc). sont présentées]. Transient scattering problem by perfectly conducting bodies is treated, directly in time domain, using the distribution theory. New integral equations for solving two dimensional scattering problems are established. Applications to metallic structures responses to electro-magnetic pulses ( Emp) illumination are presented. [ABSTRACT FROM AUTHOR]

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of Telecommunications is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Le but de cet article est d'étudier la répartition du courant le long d'un fil de longueur infinie tendu audessus d'un sol de conductivité finie. Nous utilisons la méthode de calcul déjà développée par Chang et Olsen dans le cas où la ligne est excitée symétriquement en son centre. Le formalisme adopté dans ce calcul est le formalisme des antennes. Nous donnons ensuite quelques applications numériques dans des cas où le fil est situé à proximité de l'interface airsol. Ces résultats sont ensuite comparés aux mesures sur un site expérimental, aussi bien dans le domaine fréquentiel que dans le domaine temporel. The purpose of this paper is to determine the current distribution along a line situated above a ground of moderate conductivity. To achieve that work, we use the previous theoretical work formulated by Chang and Olsen where the line is excited by a delta-function voltage generator. The antenna concept is applied in the theoretical approach. Some numerical results are given and compared to the experimental data obtained in situ through the harmonic as well as time domain. [ABSTRACT FROM AUTHOR]

Le problème du calcul du courant induit par une onde incidente sur un conducteur enterré, isolé et situé au voisinage du sol, est analysé. La solution est recherchée dans le domaine fréquentiel sur un conducteur infini. Ceci permet d'éviter le calcul des intégrales de Sommerfeld en leur substituant des intégrales qui se calculent analytiquement. Le courant induit sur un conducteur de dimension finie s'obtient en ajoutant les courants réfléchis aux extrémités pour les différents ordres successifs de réflexion. An analytical result for the current induced by a plane incident wave on a thin straight insulated wire buried in the ground and parallel to the interface is presented. Two methods are presented to solve this problem in the frequency domain; the first one uses the current on an infinite wire; the current induced on a finite wire is obtained adding to the preceding result the reflected currents of different orders. The second uses the reflection coefficients of the transmission line theory. The results are compared with those obtained from another method in which the Sommerfeld integrals are numerically evaluated. [ABSTRACT FROM AUTHOR]

La diffraction par des supports de sections triangulaire et elliptique pour antennes à réflecteurs est étudiée rigoureusement. La mise en œuvre de la transformation conforme facilite la résolution des équations intégrales résultant du problème aux limites. L'influence des supports sur les performances en polarisations principale et croisée de l'antenne est mise en évidence. Scattering by struts of triangular or elliptical cross sections for reflector antennas is rigorously studied. Conformal mapping make easier solving integral equations deduced from boundary value problem. The effects of struts on co-polarization, crosspolarization antennas performances is emphasized. [ABSTRACT FROM AUTHOR]

Le problème du calcul du courant induit par une onde incidente sur un conducteur aérien, rectiligne, filiforme, situé au voisinage du sol et parallèle à l'interface airsol est analysé. La solution recherchée est dans le domaine fréquentiel sur un conducteur infini. Ceci permet d'éviter le calcul numérique des intégrales de Sommerfeld en leur substituant des intégrales qui se calculent analytiquement. Le courant induit sur un conducteur de dimension finie s'obtient en ajoutant les courants réfléchis aux extrémités pour les différents ordres successifs de réflexion. An analytical result for the current induced by an incident wave on a thin straight wire located in the vicinity of the ground and parallel to the interface is presented. Two methods are presented to solve this problem in the frequency domain. The first one uses the current on an infinite wire; the current induced on a finite wire is obtained adding to the preceding solution the reflected currents of different orders. The second uses the reflection coefficient of the transmission line theory. The results are compared with those obtained from another method in which Sommerfeld integrals are numerically evaluated. [ABSTRACT FROM AUTHOR]

Cet article concerne le rayonnement d'une grille plane de conducteurs, illuminée par une onde électromagnétique plane. Les conducteurs constituant la grille sont équidistants et parallèles, on trouve en alternance, des conducteurs continus et des conducteurs discontinus, ces derniers pouvant être considérés comme des alignements colinéaires de doublets. La direction de propagation de l'onde plane est dans un plan perpendiculaire aux conducteurs de la grille. Le problème est résolu numériquement. Les courants sur les conducteurs sont déterminés au moyen d'un système d'équations intégrales de première espèce qu'une méthode des moments ramène à un système d'équations linéaires. La connaissance des courants permet d'obtenir les facteurs de réflexion et de transmission de la grille. On a ainsi mis en évidence un régime d'adaptation et un régime de résonance pour lesquels le facteur de transmission est en module, respectivement égal à I et à 0. Ces régimes particuliers sont obtenus pour un réseau donné à certaines fréquences. Une simulation expérimentale en guide rectangulaire a fourni des résultats en bon accord avec ceux déduits du calcul. This paper relates the scattering of a electromagnetic plane wave by a plane grating of conducting wires. The wires are parallel, equidistant and alternatively continuous and discontinuous. The discontinuous wires may be considered as dipole lines. The problem is numerically resolved. The conductor currents are determined by means of a system of first kind integral equations which is converted in a linear equations system by the moments method. The knowledge of currents permits the calculation of the reflection and transmission factors of the grating. Thus a matched state and a resonant state appear for discrete frequencies, where the transmission factor modulus is respectively 1 and 0. Experimentation on waveguide simulators gives a good agreement with numerical results. [ABSTRACT FROM AUTHOR]

L'article considère la propagation d'ondes électromagnétiques ou élastiques dans un milieu constitué de couches planes alternées de deux matériaux homogènes isotropes non dissipatifs. La direction de propagation envisagée est normale aux couches; les ondes sont supposées harmoniques planes. On retrouve l'existence de bandes de fréquences pour lesquelles les ondes se propagent et d'autres pour lesquelles ces ondes sont évanescentes. Le caractère dispersif de ces milieux est examiné. Un phénomène de ralentissement apparaît en basse fréquence. Enfin une étude détaillée donne l'expression du gain complexe, en transmission et en réflexion, du double filtre linéaire que constitue une lame feuilletée placée entre deux milieux homogènes indéfinis. Une attention particulière est portée sur le cas des milieux formés de couches isochrones. The authors consider the propagation of electromagnetic and elastic waves in a medium consisting of alternating layers of two different homogeneous isotropic and nonabsorbing substances. The waves are assumed harmonic and plane and their propagation is perpendicular to the layers. They show the existence of frequency ranges for which the wave propagation is possible and other ones where the waves are vanishing. The dispersion property of this medium is analysed; for low frequencies, the propagation velocity is shown smaller than the expected mean velocity. At last, a detailed work gives the transfer functions for transmission and reflection of the double linear filter constituted of the layered medium set between two homogeneous isotropic media. They pay attention to the isochronous layered medium. [ABSTRACT FROM AUTHOR]

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Etude de la propagation monodimensionnelle de signaux transitoires dans des « multiplets», formés par juxtaposition de plusieurs segments homogènes, d'impédances et de dimensions arbitraires: milieux stratifiés électromagnétiques ou acoustiques, aussi bien que lignes de transmission discontinues. L'accent est mis sur une approximation adaptée aux signaux de spectre étroit: ce qui réduit la description exhaustive des multiplets à trois constantes seulement, dont la détermination est établie dans le cas le plus général. Le comportement dominant est alors un retard de transmission, dénotant un «effet de freinage» par rapport au temps de parcours attendu, auquel se surajjute un effet de filtrage passebande, périodique en fréquence. L'itération d'un multiplet a pour seule conséquence de faire ressortir les deux effets précédents, le système se comportant alors en parfaite analogie avec les réseaux électriques en échelle. Les opérateurs de transmission et de réflexion d'un tel milieu itératif, placé entre deux milieux homogènes indéfinis, sont caractérisés par leurs réponses percussionnelles dont l'expression littérale est établie dans le cas non dissipatif. Par comparaison avec le comportement d'un milieu homogène qui serait substitué au milieu itératif, on constate un phénomène de réverbération de chronologie identique, mais lissé par l'effet de filtrage. Study of unidimensional propagation of transient signals through so called « multiplets», formed by juxtaposing several homogeneous sections of arbitrary impedances and sizes: electromagnetic or acoustic layered media as well as discontinuous transmission lines. The emphasis is put on an approximation, fitted to narrowband signals: which, in so doing, reduces the exhaustive description of any multiplet to three constants only, whose expressions have been fully determined in the most general case. The main behaviour is then a transmission delay, that suggests a « slowing down effect» in regard to the expected transit time, to which is added a bandpass filtering, periodic in frequency. The sole result of the periodic iteration of a multiplet is to emphasize the two previous processes: the whole system thus behaves in a very analogous manner with electrical ladder networks. The transmission and reflection operators of such iterative media, when put between two boundless yet homogeneous external media, are characterized by their impulse responses, whose literal expressions are determined in the zeroloss case. Comparing the behaviour of some homogeneous medium that could take the place of the genuine periodic medium, a reverberation process is noticed, with the same chronology but smoothed by filtering effect. [ABSTRACT FROM AUTHOR]