Auguste Laloux

Theory of the Slotted Coaxial Cable

The electromagnetic problem of the coaxial cable with a continuous slot along the outer conductor is solved taking into account the dielectric constant of tbe cable insulation. Cylindrical harmonics expansions for the inner and outer space are used. The basic difficulty is to express boundary conditions on a part of the period in Fourier series. It appears that the singularity of the fields at the edge of the outer conductor plays a key role in the uniqueness of the result. The propagation constants of the monofilar and coaxial modes are obtained with a good accuracy. It is shown that these modes have different transfer inductances.

A Computer Optimization of the Rayleigh-Ritz Method

A method has been developed to improve the use of the RayIeigh-Ritz procedure. A criterion is established, which is a measure of the cumulative improvement due to the addition of more and more terms in the series expansion. Without calculating the exact roots of determinantal equations, the convergence is accelerated by skipping unnecessary intermediate steps. The computation time is drastically reduced because the final result is obtained after only a few (not more than 5 to 7) values of determinants of increasing order. Inhomogeneneously loaded waveguides are chosen as an application because the exact solution is available to check the validity of the method. The results obtained with the method described in this paper are compared with other approximate procedures. The comparison shows a definite advantage for the suggested technique.

Radiative-transfer Equation With Surface Scattering for Ocean and Atmospheric Parameters Retrieval From Radiometric Measurements

Microwave radiometers have been used with success in the past for the retrieval of ocean surface and atmospheric parameters. However, for the most effective use of the measurements provided by these instruments, it is necessary that performant inversion algorithms be available. Existing algorithms have already proved their usefulness but are often based on statistical regressions on the measurements from some particular experiment or on artifical data sets. Progress towards better performances still remains possible. We have developed an iterative retrieval procedure based on a physical scattering and propagation model for observing the ocean surface and the intervening atmosphere. A correction for scattering by the roughened sea surface is proposed and introduced in a previously developed contracted form of the radiative transfer equation. This correction is modelled for a range of frequencies from 5 to 40 GHz, and represented, in the form of a polynomial expansion depending on two parameters only: the total atmospheric attenuation, and the wind friction velocity. Results of inversions on simulated measurements obtained with this approximate model are presented and discussed.

Application of a Variation-Iteration Method to Waveguides with Inhomogeneous Lossy Loads

An approximate technique for solving eigenvalue equations, the variation-iteration method,is commonly used in theoretics physics. A previous paper presented the application of this method to the scalar case of a dielectric slab loaded rectangular waveguide. This paper presents its extension to the complex vector case of a lossy dielectric insert loaded waveguide. Starting from an initial trial function, iterates are calculated in which the components relative to the unwanted eigenfunctions are eliminated. Both an upper and a lower bound for the unknown eigenvalues are available. Each iterate is the solution of a system of algebraic simultaneous equations. This system is solved by the successive overrelaxation method using an automatically computed optimal accelerating factor. An extrapolation technique further accelerates the convergence. This yields the attenuation and propagation coefficients for the dominant as well as several other modes, together with the electric and magnetic field configurations.

Waiting-time approximations for service systems with star polling sequence and mixed service strategies

A conservation-law-based approximation for the mean waiting times in priority service systems with a mixture of exhaustive, gated, one-limited service strategies and star polling sequence is presented. The authors generalize previous results presented by Manfield (1985) for a similar system with one-limited service at the low-priority stations. For service systems with one-limited stations the proposed approximation is a low or medium traffic approximation. However, for systems with a mixture of gated and exhaustive services the approximation is very accurate for the whole range of admissible traffic intensities. >

Mesure du Gain D’antenne par Réflectométrie

RésuméLa matrice de répartition fournit une formulation simple et une explication satisfaisante des phénomènes liés à la méthode du miroir employée pour la détermination absolue des gains d’antennes par réflectométrie. Les lacunes de cette méthode peuvent être comblées par l’emploi comme réflecteur d’une zone de Fresnel en lieu et place d’un miroir plan-infini.

Numerical Solution for Waveguioes with Inhomogeneous Lossy Loads

Waveguides containing dielectric inserts which do not extend across either of the waveguide transverse dimensions find applications in many waveguide components. In the general case, there is no analytical solution available and a numerical approach has to be used. This paper presents the solution for lossy cases. It requires the solution of a partial derivative, eigenvalue, vector, complex wave equation.