Analysis of the Doherty technique and application to a 900MHz power amplifier

In this paper, we present the study, the realisation and the measurement of an amplifier at 900 MHz using the Doherty technique. This technique is based on the large signal performance analysis of the active devices under different drive levels. The improvements made by the application of this technique were checked by simulations and measurements on a prototype made with two MESFETs transistors. For a 6 dB backoff, obtaining significant values of Power Added Efficiency was possible thanks to the application of a methodology of design, specific to this technique

New trends in characterization and modeling of High Power devices

In this paper, we present some non exhaustive measurement techniques used for characterization and modeling of high power devices. Capabilities offered by pulsed measurements can be an efficient approach to deal with self-heating effects and sometimes trapping effects encountered in microwave high power devices. Pulsed techniques allow to separate self-heating and trapping effects, making like this the modeling process easier. A pulsed RF and pulsed bias load-pull system is then described as well as a time waveform measurement system. Capabilities of these two characterization tools are illustrated with results obtained on a high power silicon bipolar transistor and on a GaAs MESFET device

Nonlinear characterization of microwave transistors by the means of pulsed I(V) and pulsed S-Parameters measurements

A versatile pulsed I(V) and 40 GHz pulsed S parameters measurement system of microwave transistors is described Capability of discrimination between thermal and trapping effects with a pulse set-up is demonstrated A method to measure electrically the thermal resistance and capacitance of transistors with a pulse set-up is proposed Finally, it is explained how to derive transistor nonlinear characteristics from these measurements for modeling purposes

Résultats géologiques d'une prospection sismique par la méthode "boomer" au large du masif armoricain méridional.

National audienc

Pliocene to Pleistocene vertical movements in the forearc of the Lesser Antilles subduction: insights from chronostratigraphy of shallow-water carbonate platforms (Guadeloupe archipelago)

An integrated stratigraphic study was conducted on the shallow water carbonate platforms of theGuadeloupe archipelago to refine the tectonic evolution of the Lesser Antilles forearc. The carbonate platforms are now dated to the Zanclean–Calabrian interval, and their demise occurred between 1.5 and 1.07 Ma. The precise chronostratigraphy allows dating of the main extensional tectonic events since the late Miocene. An initial episode occurred during the late Miocene, related to the reactivation of inherited N130°E-trending shear zones, and led to the emergence of most parts of the forearc. Subsequently, Zanclean to early Piacenzian carbonate platforms developed in association with a general subsidence of the forearc. During the late Piacenzan, a second extensional episode occurred. At this time La Désirade underwent major uplift and emergence whereas most of the forearc remained submerged. Prior to 1.07 Ma, a third north–south extensional episode occurred and led to the final demise of the carbonate platforms. Thus the forearc was characterized by general subsidence since the early Pliocene interrupted by three main extensional episodes and related differential uplifts. This suggests that the Lesser Antilles subduction is probably erosive north of latitude 15°N since c.5 Ma, related to aseismic ridge subductio

Trench Bending Initiation: Upper Plate Strain Pattern and Volcanism. Insights From the Lesser Antilles Arc, St. Barthelemy Island, French West Indies

International audienceThe upper plate deformation pattern reflects the mechanical behavior of subduction zones. Here we focus on the consequences of the entrance of a buoyant bank into the Caribbean subduction zone during the Eocene by studying the oldest exposed rocks belonging to the Lesser Antilles volcanic arc. Using a novel geochronological data set, we show that the volcanic arc activity on the island of St. Barthelemy spanned over the mid‐Eocene to early Miocene with a westward migration of the tectono‐volcanic activity, which is comparable to what has already been observed on other volcanic islands in the Lesser Antilles. The kinematics analysis allows us to identify a switch in the stress field from pure to radial extension at the Oligo‐Miocene hinge with a subhorizontal σ3 that has a mean trend of N20°. A three‐step restoration of the regional deformation indicates that this switch from pure parallel‐to‐the‐trench extension to radial extension may reflect a strain partitioning initiation affecting the upper Caribbean Plate in response to trench bending that followed the entrance of the Bahamas Bank into the subduction zone. We show that the northern end of the Lesser Antilles arc shows a tectono‐volcanic evolution which is similar to the southern one. The north‐south dichotomy in the perpendicular‐to‐the‐trench extension, 15% in the north versus 30% in the south, may reflect different slab ends that are highly curved to the north (restraining the extension in the upper plate) versus a tear to the south (allowing a larger amount of extension within the upper plate)