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Numérisation rapide d'un système synchronisé en sortie d'antennes multi-réparties tel que le Radiohéliographe de Nançay

Abstract : The Nançay Radioheliograph is the only instrument dedicated to the solar corona imaging in the 150-450 MHz frequency band. It operates on the principle of interferometry, using 47 antennas essentially distributed on the east-west (3.2 km) and north-south (2.5 km) axes. This study aims to explore a new technical concept for future radio astronomy, applied to solar interferometer. It deals with the rapid digitization of a synchronized system at the antenna sides. High speed digitization and high accuracy synchronization are the most important aspects for future radio telescopes. They make it possible to simplify radiofrequency reception chains and reduce their power consumption, as well as maintenance costs and complexity. The application to the observation of the sun, however, has some original constraints, such as the great dynamics of the signals, which are not taken into account in the current studies for future radio telescopes. The current radio telescope has an analog receiver with a centralized digitization. The switching time between each frequency (10 frequencies of 1 MHz width) in 150-450 MHz band analyzed introduce latency in solar images processing, also decrease the signal-to-noise ratio. In addition, in metric interferometry, the several lengths of coaxial cables in which the signal is transported from the antennas to the receiver always cause significant errors and fluctuations in the radiofrequency reception chains. Providing full digitization of the band (300 MHz) allows more flexibility in data processing and analyzing (frequency resolution and the ability to observe multiple bands simultaneously). This required high clock accuracy (0.7 ps of jitter) for ADCs clocks (1 GHz clock). Therefore, the main objective of this thesis is to reach a sub-ns global time synchronization of distributed networks such as radio interferometer array as the Nançay Radioheliograph. The technological leap thus induced is a growing challenge in major European and international projects.
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Submitted on : Tuesday, October 23, 2018 - 12:44:21 PM
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  • HAL Id : tel-01901916, version 1

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El Houssain Ait Mansour. Numérisation rapide d'un système synchronisé en sortie d'antennes multi-réparties tel que le Radiohéliographe de Nançay. Astrophysique [astro-ph]. Université Paris sciences et lettres, 2018. Français. ⟨NNT : 2018PSLEO001⟩. ⟨tel-01901916⟩

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