PLANCK Satellite’s Low Frequency Instrument: Study Of The Radiometers For Measuring The Cosmic Microwave Background (CMB)

Abstract

[EN] The Cosmic Microwave Background (CMB) has supposed an electromagnetic source of information for studying the properties of the early Universe, as well as for clarifying a wide range of uncertainties related to its thermal history and evolution. It is for these reasons that it has been of a great significance to measure such ancient radiation with high accuracy. In fact, a great deal of both ground and space experiments have been performed throughout history, where scientists have been facing formidable challenges in the sense of developing innovative techniques and making use of unprecedented instrumentation. Radiometry is the scientific field that takes on the study of radio receivers, analyses their characteristics (sensitivity, resolution, signal model, circuitry...) and explores different measurement methods in order to obtain more and more rigorous results. It is in this sense that the Planck Mission from the European Space Agency (ESA) has been considered one of the biggest breakthroughs in the last years: it has been able to measure the CMB radiation with unique sensitivity and angular resolution, and has revealed both CMB temperature and polarization maps. Hence our main objective is going to be to provide an overview of radiometry concepts and then focus on the so-called differential or pseudo-correlation radiometers used in the Planck Satellite. Besides, the particular case of the mentioned receptors will give us the opportunity to develop a specific analytical model for them, where our main goal will be to combine the theoretical results with simulation-based ones, strengthening in this way the successful performance and great utility of the technique employed in Planck Mission. Concerning the structure of this work, in the upcoming second chapter we will give a general insight of the most important events through the Universe’s thermal history in order to understand the origin of the CMB and its properties; moreover, we will also briefly mention some of the numerous experiments made for its measurement. Chapter 3 will be responsible for analysing different concepts of radiometry and presenting the most known radiometer types: the total power radiometer, the Dicke radiometer and the correlation radiometer. We will then be able to introduce ourselves in the study of the Planck Mission and the main features of its Low Frequency Instrument (LFI) will be explained (chapter 4). The analytical model of the LFI’s pseudo-correlation radiometers will be developed in chapter 5, where we will also complete an analysis of systematic effects such as noise temperature and gain fluctuations. Chapter 6 will consist of simulations carried out with Advanced Design System (ADS) software: we will describe the simulation technique used and present the results achieved. The work will come to an end with some conclusions and future work discussion