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

Calculation of conducted EMI generated by single-ended primary inductance converter

International audienceThis paper deals with the problem of conducted electromagnetic disturbances generated by a single-ended primary inductance converter (SEPIC) switching power supply for radar applications. In the proposed model the passive components are replaced by their high frequency (HF) equivalent models and the active elements by the interference sources. The six windings transformer, which is one of the passive elements of the switching power supply allows the adaptation of voltage levels and provides galvanic isolation between input and output. It will be modeled by: a simplified model and then by a model taking into account coupling between the leakage inductances. The accuracy of each model is established by comparing the simulation results of conducted electromagnetic interference (EMI) to measurement results

Pulsed gate bias control of GaN HEMTs to improve pulse-to-pulse stability in radar applications

International audienceA significant improvement is demonstrated in the measured pulse-to-pulse stability of an S-band 6 W GaN high electron mobility transistor (HEMT) power amplifier by generating an appropriate pulse of the gate bias and thus a warm-up drain current just before each radio-frequency (RF) pulse of a periodic and coherent radar burst. The amplitude and the width of this gate bias pulse preceding each periodic RF pulse of the burst are experimentally varied to investigate the trade-off between the improvement of pulse-to-pulse stability and the total power-added efficiency. Finally, this technique of synchronised warm-up gate bias pulse demonstrated a 10 dB improvement of measured amplitude pulse-to-pulse stabilities to meet the critical stability requirement below −55 dB for the RF power amplifier

Design of a 55 W packaged GaN HEMT with 60% PAE by internal matching in S-band

International audienceThis paper reports a package synthesis method in order to ensure good performances in PAE, output power and bandwidth. The internal matching circuits of the optimized package enable to reach the best impedance pre-matching at fundamental frequencies and also to confine the harmonic impedances seen by the internal GaN power bar into safe-efficiency regions whatever the external impedances presented to the package at second harmonic frequencies. In a 50Ω environment, the packaged GaN HEMT delivers 55 W output power associated with 60% PAE and 13.3 dB power gain at 2.7 GHz. By optimizing source and load impedances at the fundamental frequencies, the packaged GaN HEMT demonstrates more than 58% PAE from 2.6 GHz to 3.0 GHz

Study of electromagnetic field stress impact on SiGe heterojunction bipolar transistor performance

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Study of electromagnetic field stress impact on SiGe heterojunction bipolar transistor performance

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Impact of the duty cycle on the pulse-to-pulse stability of a GaN power amplifier

International audienceThis paper presents a heterodyne measurement system of the pulse-to-pulse (P2P) stability and its application to time-domain measurements of a GaN HEMT microwave power amplifier. Envelope and P2P stability measurements are performed for an irregular RF pulse train which integrates a long silence between each pulse sequence. This paper is focused on the impact of RF pulse width and duty cycle on each pulse sequence. Coherent measurements of time-domain envelope and P2P stability are performed on a 10W S-band GaN power amplifier. Indeed, one aim of this work is to illustrate the great impact of temperature and trapping effects on the envelope response and P2P stability of GaN power amplifiers

Determination of the self-heating temperature of AlGaN/GaN HEMTs in radar operation

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