Méthodes d’analyse et de synthèse de quelques “ microantennes” à large bande en mode quasi transversal électromagnétique

The transmission line model has been utilized to determine the input impedance, the bandwidth, the radiation patterns and the mutual impedance of several microstrip antennas such as the arbitrary shape patch antennas and the wideband flat dipole which is an hybrid radiating source. We suppose that the dominant mode of propagation is the quasiTem one having negligible variation of fields in the transverse direction. Nevertheless a general scattering problem of an arbitrary shaped tridimensional antenna solved by moments method and the finite difference approach applied to integral equations has explained the very large bandwidth microstrip antenna behaviour. The wideband flat dipole has been used in flat arrays, with more than several hundred of such elements, and in microstrip phased arrays with beam steering in a large angular sector.     

Sur les méthodes de calcul de l’exposant linéique de propagation et d’impédance caractéristique des câbles aériens et enterrés

The propagation constant of a line or a cable, and its characteristic impedance represent two parameters which are needed in order to calculate the variation as a function of the time of a current induced by an emp.For the aerial lines expressions which take into account the presence of the soil could be developed but the case of the buried conductors is of a more difficult approach. The aim of this study is to present solutions introduced by different authors and to compare them with a calculation method for the propagation constant using iterations, proposed by the authors. If this value is known it is shown that the characteristic impedance calculation of buried cables can be improved by avoiding the necessity to compute with a reasonable precision the impedance of the ground.     

Méthode originale d’analyse du diagramme de diffraction en puissance d’une cible radar en vue de la reconnaissance des formes

Aircraft modeling is often accomplished by replacing the skin of the aircraft by several conveniently placed scatterers. We show that a Radar Cross Section (rcs)diagram can be described as a sum of bipoint s diagrams and that this decomposition can be greatly simplified. Then we consider the extraction of bipoints parameters from the knowledge of a diagram of radar cross section in the far field. This study exhibits that the bipoint function is a system of Chebyshev polynomials of the first or second kind. After a changement of variables,the bipoint function becomes then a A.M. function. By a Fourier analysis of transformed rcs,we can find the lengths between the points and the amplitudes. This study can be also extended to a multipoint in a line which radiates with spatial directivity.     

Étude du comportement d’une boucle de Costas en modulation MAQ 16 en présence d’évanouissements sélectifs

This paper gives the variance of the phase recovered by a conventional quadriphase Costas loop in 16 Qam modulation in the presence of a selective fading, represented as a three rays simplified model. The power spectral density of the phase error is computed using a spectral estimation technique. The phase error variance is evaluated for different values of the fade depth, the location of the maximum attenuation in the frequency band and the delay of the reflected ray. Finally the relation between the performance degradation and phase noise is given, assuming a gaussian p.d.f. of the phase error.     

Amplitude et polarisation des ondes UBF détectées à bord du satellite GEOS-I. Méthodes d’analyse,problèmes rencontrés et solutions pratiques

A method for analysing polarized signals is briefly described. This method is applied to the instantaneous frequency, amplitude and polarization of Ulf waves detected in a frame of reference rotating at frequency close to the one of the waves being studied. This method is being applied to the data obtained from the European satellites Geos-1and 2,which are stabilized by rotation at about 0.17Hz. The local static magnetic field has a strong component perpendicular to the satellite rotation axis, therefore inducing in the antennas a strong component at the rotating frequency. Part of this parasitic signal is eliminated directly on board the satellite owing to a despinsystem. But the remaining disturbance affects all the frequencies of the power spectrum with a ratio depending on the relative value of the integration time and the rotation period. This modification of the spectrum is studied in detail and the authors demonstrate that it can be avoided with an easy method of signal processing at the ground. Both methods used jointly allow the production as a routine basis of experimenter summariesenabling to know at each moment the main characteristics of the waves being detected.     

Le gradient équivalent nouvelle détermination et calcul graphique

Annals of Telecommunications - Pour caractériser l'influence de l'atmosphère sur la propagation transhorizon, il est nécessaire d'introduire deux paramètres,...