Multi-frequency fine resolution imaging radar instrumentation and data acquisition

Development of a dual polarized L-band radar imaging system to be used in conjunction with the present dual polarized X-band radar is described. The technique used called for heterodyning the transmitted frequency from X-band to L-band and again heterodyning the received L-band signals back to X-band for amplification, detection, and recording

Modélisation et estimation des instabilités des émetteurs radars à l'état solide

La stabilité pulse à pulse est une caractéristique primordiale d'un émetteur radar de surface à impulsions car elle limite la détection des cibles dont en particulier celles de faible Surface Equivalente Radar (SER) dans un contexte contraignant (clutter important). L'amélioration des performances des radar passe par une analyse fine des sources possibles de perturbations tels que les variations thermiques des composants de puissance et la fluctuation de l'alimentation. La modélisation statistique est un outil puissant pour exploiter ce type de données radar. Un modèle statistique de signal émis est proposé, il comporte outre l'impulsion dont la forme est variable en fonction de la température et de la fréquence d'émission, un processus multiplicatif qui traduit le comportement basse fréquence de l'alimentation et un bruit additif. Nous proposons ensuite trois coefficients de stabilité de phase de l'alimentation, de l'impulsion en régime transitoire et en régime stationnaire. Nous finirons par analyser les résultats de leurs estimations au regard des conditions thermique de l'expérimentation et de la fréquence à l'émission

Electrical conductivity in granular media and Branly's coherer: A simple experiment

accepted for publication in American Journal of Physics (to be published between February 2005 and June 2005)We show how a simple laboratory experiment can illustrate certain electrical transport properties of metallic granular media. At a low critical imposed voltage, a transition from an insulating to a conductive state is observed. This transition comes from an electro-thermal coupling in the vicinity of the microcontacts between grains where microwelding occurs. Our apparatus allows us to obtain an implicit determination of the microcontact temperature, which is analogous to the use of a resistive thermometer. The experiment also illustrates an old problem, the explanation of Branly's coherer effect - a radio wave detector used for the first wireless radio transmission, and based on the sensitivity of the metal fillings conductivity to an electromagnetic wave

An ultra-high switching frequency step-down DC-DC converter based on Gallium Arsenide devices

A 50MHz to 100MHz dc-dc power converter using Gallium Arsenide power switches is studied. GaAs Schottky rectifiers with high breakdown voltage and very small Ron x Con switching quality factor have been fabricated. A 10V to 5V (or 8V) prototype with an output power of 2.6 Watts and a power efficiency of 77% has been reported

0.3µm-N-HIGFET capabilities for microwave power apllications

0.3µm HIGFET transistors have been realized for microwave power applications. Power measurements at 3.5GHz using load-pull testbench have been carried out. Transistors exhibit an output saturated power of 16dBm and a power density of 370mW/mm for a 3V drain-to-source voltage

HETEROSTRUCTURE FIELD EFFECT TRANSISTOR, PHYSICAL ANALYSIS AND NEW STRUCTURES

Les principaux phénomènes physiques qui se produisent dans les MODFET conventionnels AlGaAs/GaAs sont décrits brièvement : structures quantiques, propriétés de transport - influence du champ électrique. La modélisation des composants permet d'obtenir des informations très utiles sur leur fonctionnement et les principaux effets physiques qui interviennent tout en permettant d'en prévoir les performances. Les problèmes posés par les réalisations technologiques ou le fonctionnement dans des conditions particulières (haute température, grande puissance) sont examinés. On décrit les nouvelles structures telles que les MODFET inversés, les SISFET et les MODFET à couches pseudomorphiques ainsi que leurs performances potentielles.Physical phenomena that occur in conventional AlGaAs-GaAs MODFETs are briefly described. This covers quantum effects, carrier transport properties, influence of electric field... Progress in device modeling allow to obtain valuable information on device behaviour as well as various intervening physical effects and to predict the performance. Limitations resulting from both technological imperfections and specific device operations, e.g. low temperature, large power, are investigated. New structures such as inverted MODFET, SISFET, and pseudomorphic MODFETs are described and their potential capabilities are discussed

Quasi-2D analysis of travelling gunn domains in microwave MESFET's

We present a numerical analysis of travelling Gunn domains in GaAs MESFET's based on a quasi-2D hydrodynamical model. The results are shown to be quite accurate in comparison to Monte Carlo simulations, despite the simplicity of the quasi-2D model. A microscopic description of the domain propagation is also given

Optimization of multiheterojunction AlGaAs/GaAs HEMT's for microwave power amplification

A theoretical and experimental study concerning a three channels power HEMT is presented. The structure has been, first, optimized using an adequate simulation. Then many technological realizations have been achieved at the laboratory. Measurements performed with these devices give results very encouraging and permit to foresee superior performances relatively to that of GaAs power MESFET's

5th edition of the « Journées Nationales Microondes »

No abstract availabl