CMB Telescopes and Optical Systems

The cosmic microwave background radiation (CMB) is now firmly established as a fundamental and essential probe of the geometry, constituents, and birth of the Universe. The CMB is a potent observable because it can be measured with precision and accuracy. Just as importantly, theoretical models of the Universe can predict the characteristics of the CMB to high accuracy, and those predictions can be directly compared to observations. There are multiple aspects associated with making a precise measurement. In this review, we focus on optical components for the instrumentation used to measure the CMB polarization and temperature anisotropy. We begin with an overview of general considerations for CMB observations and discuss common concepts used in the community. We next consider a variety of alternatives available for a designer of a CMB telescope. Our discussion is guided by the ground and balloon-based instruments that have been implemented over the years. In the same vein, we compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT). CMB interferometers are presented briefly. We conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and Planck, to demonstrate a remarkable evolution in design, sensitivity, resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1: Telescopes and Instrumentatio

Understanding synthesis imaging dynamic range

We develop a general framework for quantifying the many different contributions to the noise budget of an image made with an array of dishes or aperture array stations. Each noise contribution to the visibility data is associated with a relevant correlation timescale and frequency bandwidth so that the net impact on a complete observation can be assessed. All quantities are parameterised as function of observing frequency and the visibility baseline length. We apply the resulting noise budget analysis to a wide range of existing and planned telescope systems that will operate between about 100 MHz and 5 GHz to ascertain the magnitude of the calibration challenges that they must overcome to achieve thermal noise limited performance. We conclude that calibration challenges are increased in several respects by small dimensions of the dishes or aperture array stations. It will be more challenging to achieve thermal noise limited performance using 15 m class dishes rather than the 25 m dishes of current arrays. Some of the performance risks are mitigated by the deployment of phased array feeds and more with the choice of an (alt,az,pol) mount, although a larger dish diameter offers the best prospects for risk mitigation. Many improvements to imaging performance can be anticipated at the expense of greater complexity in calibration algorithms. However, a fundamental limitation is ultimately imposed by an insufficient number of data constraints relative to calibration variables. The upcoming aperture array systems will be operating in a regime that has never previously been addressed, where a wide range of effects are expected to exceed the thermal noise by two to three orders of magnitude. Achieving routine thermal noise limited imaging performance with these systems presents an extreme challenge. The magnitude of that challenge is inversely related to the aperture array station diameter.Comment: 27 pages, 24 figures, accepted in A&A, final versio

Microwave performance characterization of large space antennas

Performance capabilities of large microwave space antenna configurations with apertures generally from 100 wavelengths upwards are discussed. Types of antennas considered include: phased arrays, lenses, reflectors, and hybrid combinations of phased arrays with reflectors or lenses. The performance characteristics of these broad classes of antennas are examined and compared in terms of applications

Beam ripple modelling in wideband dual-reflector antenna systems

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Efficient modelling of the rapid far-field frequency variations found in the radiation of electrically small dual reflector antennas is of high interest due to their increasing use in array configurations for interferometry. These rapid variations, most discernible in broadside directivity across frequency, are a result of internal field interference between the radiation from the feed and reflector apertures causing chromatic aberration. Their quasi-sinusoidal nature presents a significant challenge from a modelling perspective, as computationally expensive samples at the Nyquist rate or above are required to capture the ripple during frequency interpolation. This thesis presents the design of a physics based surrogate model able to reconstruct the ripple with a sparse set of samples independent of its frequency, and therefore, at a mere fraction of the Nyquist rate, significantly reducing the computational cost of wideband characterisation. The model is designed to assist during the evaluation of reflector geometry and feed suitability through interpolation of MoM or PO solutions with the characteristic basis function expansion method (CBFP). An adaptive sampling approach is adopted to minimise the number of direct antenna simulations needed for the generation of an accurate global model able to facilitate rapid design and analysis. The surrogate model implementation shown here is able to capture the chromatic aberration ripple inherent to reflector surfaces of several tens of wavelengths with a sample density ≈ 1 10 th of the Nyquist rate per octave bandwidth, for analytical Gaussian primary patterns. Prediction error is typically less than 10 % of the ripple amplitude, provided enough samples are used such that the CBFP expansion successfully isolates geometric beam features. A higher sampling density is required for primary patterns from practical antennas due to their effects on the macro behaviour of the secondary pattern across frequency, however, this is typically below 1 4 of Nyquist density. Overall, far-field radiation pattern prediction error is tied to the number of frequency samples available to train the CBFP expansion, therefore, any modelling limitation previously imposed by the chromatic aberration ripple is removed.AFRIKAANSE OPSOMMING: Die effektiewe modellering van vinnige ver-veld variasies gevind in die radiasie patroon van elektriese klein dubbel reflektor antennas is van groot belang a.g.v. die toenemende gebruik van antenna samestellings vir interferometrie. Hierdie vinnige variasies, mees prominent in die bre¨ekant gerigtheid oor frekwensie is a.g.v. die interne veld interferensie tussen die voer- en reflektor openinge se radiasie, veroorsaak deur chromatiese afwyking. Vanaf ‘n modellerings perspektief bied die kwasi-sinusvormigheid van die variasies ‘n groot uitdaging, omrede duur berekenings monsters nodig is, teen die Nyquist-koers of ho¨er, vir suksesvolle opvang van die rimpel tydens frekwensie interpolasie. Hierdie tesis handel oor die ontwerp van ‘n fisika-gebaseerde surrogaat model, in staat daarvan om die rimpel vanaf ‘n stel yl monsters onafhanklik van die frekwensie te rekonstrueer, teen ‘n blote breukdeel van die Nyquist-koers, voor, wat gevolglik tot ‘n groot afname in die berekenings koste vir bre¨eband karakterisering lei. Die model dien as ‘n hulpmiddel tydens die evaluering van reflektor geometrie en voer geskiktheid deur interpolasie van die moment metode en fisiese optika oplossings met die karakteristieke basis funksie uitbreidings (KBFU) metode te kombineer. ‘n Aanpasbare steekproef benadering word aangeneem om die aantal direkte antenna simulasies, nodig vir die generasie van akkurate globale modelle vir vinnige prototipering en kalibrasie, te minimeer. Die surrogaatmodel implimentering wat hier voorgelˆe word, is daartoe instaat om die chromatiese aberrasie rimpel, inhirent tot reflektoroppervlakte van verskeie tientalle golflengtes met ’n monster digtheid ≈ 1 10 th van die Nyquist koers per oktaaf bandwydte vir analitiese Gauss primˆere patrone, op te vang. Die voorspellingsfout is tipies minder as 10% van die rimpelamplitude, mits genoeg monsters gebruik word sodat die KBFU die geometriese balk kenmerke suksesvol kan isoleer. ’n Ho¨er steekproefdigtheid word benodig vir primˆere patrone van praktiese antennas a.g.v. hul effek op die makro gedrag van die sekondˆere patroon oor frekwensie, alhoewel dit tipies onder 1 4 van die Nyquist-digtheid is. Algemene ver-veld radiasie patroon voorspellingsfout is gekoppel aan die aantal frekwensie monsters beskikbaar om die KBFU op te lei, daarom is enige modellerings beperkinge voorheen opgelˆe deur die chromatiese aberrasie verwyder.Master

Design and analysis of a quasi-optical beam combiner for the QUBIC CMB interferometer

In winter 2009 a number of physicists met in Paris to discuss the prospect of observing the CMB B-mode polarization using a novel technique called bolometric interferometry. This was the first meeting of what would later become the QUBIC collaboration. In this thesis we discuss the scientific reasons for CMB observation, we present a detailed explanation of how QUBIC will use bolometric interferometry to measure CMB polarization and in particular we discuss the author's contribution to the project. As part of the sub-mm optics research group in the National University of Ireland Maynooth the author was charged with the design and modeling of the optics that would focus the beam from the sky onto the bolometric detectors. This thesis describes various types of re ecting and refracting optics that were investigated. The results we present are useful not only for the QUBIC instrument, but for the design of imaging experiments in general. Detection of CMB B-mode polarization is one of the supreme goals of modern cosmology. The faintness of this signal, combined with the interferometric observing technique, places extreme performance specifications on the QUBIC optics. Fortunately, as we shall show, there are types of well-known re ecting and refracting telescopes that are suitable for QUBIC. In this thesis I propose a design for the quasi-optical combiner that will perform as required

System engineering for radio frequency communication consolidation with parabolic antenna stacking

2020 Fall.Includes bibliographical references.This dissertation implements System Engineering (SE) practices while utilizing Model Based System Engineering (MBSE) methods through software applications for the design and development of a parabolic stacked antenna. Parabolic antenna stacking provides communication system consolidation by having multiple antennas on a single pedestal which reduces the number of U.S. Navy shipboard topside antennas. The dissertation begins with defining early phase system lifecycle processes and the correlation of these early processes to activities performed when the system is being developed. Performing SE practices with the assistance of MBSE, Agile, Lean methodologies and SE / engineering software applications reduces the likelihood of system failure, rework, schedule delays, and cost overruns. Using this approach, antenna system consolidation via parabolic antenna stacking is investigated while applying SE principles and utilizing SE software applications. SE / engineering software such as IBM Rational Software, Innoslate, Antenna Magus, ExtendSim, and CST Microwave Studio were used to perform SE activities denoted in ISO, IEC, and IEEE standards. A method to achieve multi-band capabilities on a single antenna pedestal in order to reduce the amount of U.S. Navy topside antennas is researched. An innovative approach of parabolic antenna stacking is presented to reduce the amount of antennas that take up physical space on shipboard platforms. Process simulation is presented to provide an approach to improve predicting delay times for operational availability measures and to identify process improvements through lean methodologies. Finally, this work concludes with a summary and suggestions for future work

Antennas everywhere - from space to undersea - design, optimizations and new techniques for spaceborn, ground based and marine antennas

The present dissertation gathers the most significant researches and achievements of its author in the antenna domain. The text is organised in three main parts that are intended to guide the reader through a theoretical and technological excursus on antennas solutions, from space to undersea. Each part aims at showing the answer to each of the following questions, respectively: How a spaceborne antenna shall be? How a ground-based antenna shall be? How a media penetrating antenna shall be? In the frame of a collaboration with the European Space Research and Technology Centre (ESTEC) of the European Space Agency (ESA), the author has been involved, after completing on site (in The Netherlands) his M.Sc. degree in 2011, in a research on the optimisation of the scanning properties of confocal dual reflector antenna systems for spaceborne applications. As part of his permanent assignment, since 2012, as consultant at the ESA’s European Space Operations Centre (ESOC), Germany, the author is responsible of different sustaining and investment projects on existing and new ground antenna terminals for space missions. Some of the projects are presented in this work. Together with the group of electromagnetism of the University La Sapienza of Rome, the author has treated problems related to the electromagnetic deep penetration of lossy media using deep penetrating new antenna solutions. The text is organized into five chapters. Chapter 1 is an introduction and deals with the historical background of modern antennas technologies and layouts and with the fundamental parameters for the analysis of antenna systems related to space and terrestrial contexts. Chapter 2 presents the major achievements of a study on a dual confocal offset antenna configuration for space applications. In particular the optical aberrations caused by the offset arrangement are analysed in order to validate the system introduced as an interesting solution for compact, light and simple payload antennas. Chapter 3 introduces to the world of ground based antennas and provides some interesting hints on a wide range of ground antenna types. Several designing solutions are proposed with the aim of optimizing the desired available gain for the various applications, from the tracking of a space launcher to the communication with spacecraft at the edge of the solar system. An in-depth study is presented on the upgrade of a radio telescope into a ground terminal for the support of deep space missions, addressing to the required versatility of the antenna layouts and to the sustainability of the ground station environment. In Chapter 4, the possibility of achieving the electromagnetic deep penetration of lossy media is analysed. A new design solution, able to generate inhomogeneous waves, similarly to what performed by leaky wave antennas, is introduced. This layout is of extreme interest for its flexibility and for its potentiality of application, as for instance the deep penetration of seawater. Chapter 5 recaps the conclusions of the entire dissertation showing that the world of antennas is much wider than one may think at first sight and innovative solutions are always behind the corner