Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 129-133. / by A. Colbert Reisz. / Ph.D.

This thesis presents methods for modeling the pattern of large axisymmetric paraboloidal focus-fed reflector antenna systems. The intended application of these methods is to improve the performance of time-domain interference canceling (TDC) in radio astronomy. The first method yields a closed-form expression for the antenna pattern with parameters accounting for the focal ratio and feed pattern. In subsequent adaptive methods, parameters of this model are calculated using measurements of interference signals. The corrected pattern model improves the prediction of the change in the true pattern for future times. The methods are compared by (1) comparing the error in the pattern model with respect to the true pattern and (2) comparing the pattern value update period required to achieve a specified level of residual interference when used in TDC. The efficacy of the pattern modeling methods is demonstrated by showing that the error in the pattern model decreases and the pattern value needs to be updated at a much slower rate for effective TDC. / Master of Science / Radio astronomy is the study of astronomical objects at radio frequencies. Radio telescopes, employing large reflector antennas, are often used to detect and measure extremely weak signals received from distant astronomical bodies. A growing problem for radio astronomy is that human-made communication satellites, orbiting around the earth, interfere with the radio signals. A satellite traversing the antenna pattern interferes with the signal of interest and contaminates it. Presently, this interference is managed by scheduling (avoidance) or by deleting the afflicted data. However, satellite interference is expected to become worse in the future with the increase in the number of satellites in orbit. Therefore, it will become increasingly difficult to avoid the interference by scheduling observations, and there may be too much afflicted data to delete. Hence, more sophisticated techniques may soon be required. One possible method for interference mitigation is Time Domain Canceling (TDC), which is the method addressed in this thesis. This method involves generating an estimate of the interference signal from the interfering satellite. This estimated interference signal is then subtracted from the measured signal contaminated with the interference signal. Ideally, this process should completely remove the interference while preserving the signal of interest and the noise (important in radio astronomy). To improve the accuracy of estimation of the interference signal, we require precise knowledge of the antenna pattern because the interference signal is seen through the antenna pattern. However, the pattern for large reflector antennas employed in radio telescopes is not precisely known and is often difficult to measure or analyze. In this work, we address this problem of lack of pattern knowledge by developing methods for modeling the pattern of large axisymmetric paraboloidal focus-fed reflector antenna systems. We have shown that the pattern model can be significantly improved using measurements of the interference signal in real time. We have also demonstrated that the performance of TDC improves with the incorporation of the developed pattern models.

The Radio Neutrino Observatory in Greenland (RNO-G) is a multidisciplinary, multinational collaboration which uses antennas to detect neutrino interactions with arctic ice sheets. Neutrinos are formed from nuclear reactions; predominant sources include nuclear reactors, stars, supernovae, and the big bang. They rarely interact with normal matter and thus travel from origin to destination relatively unimpeded, with applications including tracking nuclear weapons tests and supernovae. Measurements of galactic neutrino flux can provide information about how the universe developed and its current evolution. Neutrino interactions produce signals from 100 to 1000MHz. Current RNO-G antennas operate over only a portion of this band; 200MHz for horizontally polarized (Hpol) and 400MHz for vertically polarized (Vpol). In this thesis, multiple lengths of Hpol antennas are combined, and exponentially tapered geometry is added to the Vpol antenna to improve performance. Both polarizations are combined into one structure to improve observatory performance. This thesis details the design, fabrication, and testing of a new RNO-G antenna iteration. Each design is compared to frequency, gain, matching, and size requirements. Two variations of the final design are fabricated and tested, with performance compared to simulation.

Radio astronomy is the science of observing the universe at radio frequencies. In recent years, radio astronomy has faced a growing interference problem as radio frequency (RF) bandwidth has become an increasingly scarce commodity. Communication systems such as Earth orbiting communication satellites creates severe interference to the radio telescopes. This thesis proposes an algorithm to mitigate the radio frequency interference (RFI) from the Iridium satellite system. A technique is presented here to detect the downlink signal of Iridium, estimate the parameters of the signal, synthesize the noise-free version of the signal and finally subtract the recreated signal from the radio telescope output. Using both simulated and real data captured by a radio telescope testbed, we demonstrate that for Iridium bursts with 20 dB signal to noise power ratio (SNR), the proposed algorithm achieves more than 15 dB cancellation. The method proposed here can be implemented using present-day digital signal processing hardware and software. A performance analysis of this proposed cancellation scheme in the radio astronomy RFI mitigation regime is presented. / Master of Science

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A methodology is developed to manage the large number of RFI Culprits on a new Radio Telescope location such as the South African site being developed in the Karoo, both during construction and ongoing operations. The requirement for RFI control is presented, with brief reference to the more traditional methods used by other Radio Telescope observatories. The new approach is then presented, based on methods used in the engineering field of Logistic Engineering. Three case studies are used to illustrate how the approach can be applied. Finally, recommendations are made on how the approach can be implemented for new Radio Telescope projects. / AFRIKAANSE OPSOMMING: ‘n Metodolgie word ontwikkel vir die beheer van die groot aantal Radiofrekwensiesteurings oortreders by ‘n nuwe Radio Teleskoop terrein, soos die Suid Afrikaanse terrein wat huidiglik in die Karoo ontwikkel word. Die metodolgie geld beide gedurende konstruksie en gedurende bedryf. Die behoefte vir RFS beheer word aangebied, met kortlikse melding van die meer tradisionele metodes wat ander Radio Teleskoop Sterrewagte gebruik. ‘n Nuwe aanslag, gebaseer op die metodolgieë van Logistieke Ingenieurswese, word dan aangebied. Drie gevallestudies wys hoe hierdie nuwe aanslag toegepas kan word. Laastens word aanbevelings gemaak om hierdie nuwe aanslag met nuwe Radio Teleskoop projekte te implimenteer.

This thesis describes the analysis of pointed thermal Sunyaev-Zel'dovich (SZ) effect data from observations using the Cosmic Background Imager 2 (CBI2). CBI2 is an upgrade to the original Cosmic Background Imager, with antennas that have twice the effective collecting area, and hence provide greater sensitivity on longer baselines. Observations of the thermal SZ effect constrain the line-of-sight integrated gas pressure within clusters of galaxies and, when combined with X-ray data, provide an excellent tool for deriving the physical properties of these large structures. The CBI2 SZ data combine relatively low-resolution with a large field-of-view, and can therefore be used to constrain the gas properties of medium-redshift clusters out to the virial radius. By jointly fitting a suitable analytical model to SZ data and X-ray surface brightness data, it is possible to obtain constraints on the temperature and total mass of the cluster. For the analysis work presented in this thesis I choose to parametrise the gas based upon the known behaviour of the entropy, and the total mass by the Navarro, Frenk and White (NFW) prescription. This model is tested against Hydrodynamic/N-body simulations and is found to reproduce the radial behaviour of key cluster properties. The CBI2 observations presented in this work focus on the REFLEX-DXL clusters, an X-ray luminous sub-sample of the REFLEX survey at z ~ 0.3, which have previously published X-ray surface brightness data. The Bullet Cluster, a significant merger system, is a member of this sample and is presented here as a case study for use of the entropy-based model. The derived total mass and gas mass fraction of this cluster are found to be consistent with results from previous X-ray observations. The derived properties from the REFLEX-DXL sample are used to construct a preliminary set of SZ scaling relations out to the virial radius, and are found to be consistent with the self-similar model for massive clusters.

The presentation highlights research on theory, design, EM modeling, fabrication, packaging, and measurement of GaAs Monolithic Microwave Integrated Circuits (MMICs). The goal of this work is to design MMIC LNAs with low noise figure, high gain, and wide bandwidth. The work aims to develop GaAs MMIC LNAs for the application of RF front-end receivers in radio telescopes. GaAs MMIC technology offers modern radio astronomy attractive solutions based on its advantage in terms of high operational frequency, low noise, excellent repeatability and high integration density. Theoretical investigations are performed, presenting the formulation and graphical methods, and focusing on a systematic method to design a low noise amplifier for the best noise, gain and input/output return loss. Additionally, an EM simulation method is utilized and successfully applied to MMIC designs. The effect of packaging including the wire bond and chassis is critical as the frequency increases. Therefore, it is modeled by full-wave analysis where the measured results verify the reliability of these models. The designed MMICs are validated by measurements of several prototypes, including three C/X band and one Q band MMIC LNAs. Moreover, comparison to similar industrial chips demonstrates the superiority of the proposed structures regarding bandwidth, noise and gain flatness, and making them suitable for use in radio astronomy receivers. / Graduate / 2020-05-01

Submitted by Verena Pereira (verenagoncalves@uefs.br) on 2018-07-11T22:28:24Z No. of bitstreams: 1 TFC - MARCELO LAGO ARA?JO.pdf: 15427093 bytes, checksum: 0f71c2c794a5b17a6bd6de1c0dedb9df (MD5) / Made available in DSpace on 2018-07-11T22:28:24Z (GMT). No. of bitstreams: 1 TFC - MARCELO LAGO ARA?JO.pdf: 15427093 bytes, checksum: 0f71c2c794a5b17a6bd6de1c0dedb9df (MD5) Previous issue date: 2017-12-21 / With Radio Astronomy we can study the Universe through the radio waves that reach us, taking advantage of the windows of atmospheric observation. It is an Astronomy branch that covers the development of new technologies for the capture, detection, storage and analysis of immense amounts of data. In a scenario of several technological innovations, the scientific developments from Radio Astronomy have an impact on other fields of knowledge. The study of this Science is a pertinent resource for the teaching of components of Physics, in an interdisciplinary way. Before proposing the Educational Products, with Radio Astronomy as its theme, it was necessary to experience its practical aspects, from the construction of prototypes to radioastronomical observations with experimental radio telescopes, such as Radio Jove. Field experiences have become a practice that can be adopted by other teachers. They provided knowledge for the development of the proposed Educational Products: Hertz Experiment, Adapted Galena Radio, Io-Jupiter Simulator, Pulsar Simulator, Ku Band Radio Telescope, RCFM Simulator, Teacher Workshop and Website, repository of Educational Product guides. They also collaborated on the developed methodology that includes the proposal of classroom application with the use of Conceptual Maps and V Diagrams, for diagnosis, evaluation and conduction of the experiments. The products were tested and evaluated qualitatively, from their application in events of scientific dissemination in formal and non-formal teaching environments. In these evaluations, they obtained a positive qualification that indicates their relevance to the promotion of meaningful learning, based on the items analyzed / Com a Radioastronomia podemos estudar o Universo por meio das ondas de r?dio que chegam at? n?s, aproveitando as janelas de observa??o atmosf?rica. ? um ramo da Astronomia que abrange o desenvolvimento de novas tecnologias para a capta??o, detec??o, armazenamento e an?lise de imensas quantidades de dados. Num cen?rio de diversas inova??es tecnol?gicas, os desenvolvimentos cient?ficos oriundos da Radioastronomia t?m impacto em outros campos do saber e o estudo desta Ci?ncia ? um recurso pertinente para o Ensino de componentes da F?sica, em car?ter interdisciplinar. Antes de propor os Produtos Educacionais, tendo a Radioastronomia como tema, foi necess?rio vivenciar seus aspectos pr?ticos, desde a constru??o de prot?tipos ?s observa??es radioastron?micas com radiotelesc?pios experimentais, como o Radio Jove. As viv?ncias em campo se constitu?ram numa pr?tica que pode ser adotada por outros professores. Forneceram conhecimentos para o desenvolvimento dos Produtos Educacionais propostos: Experimento de Hertz, R?dio de Galena Adaptado, Simulador de Io-J?piter, Simulador de Pulsar, Radiotelesc?pio Banda Ku, Simulador RCFM, Oficina para Professores e o s?tio na Internet, reposit?rio dos roteiros dos Produtos Educacionais. Tamb?m colaboraram para a metodologia desenvolvida que inclui a proposta de aplica??o em sala de aula com a utiliza??o de Mapas Conceituais e Diagramas em V?, para diagn?stico, avalia??o e condu??o dos experimentos. Os produtos foram testados e avaliados qualitativamente, a partir de sua aplica??o em eventos de divulga??o cient?fica em ambientes formais e n?o formais de ensino. Nestas avalia??es, obtiveram qualifica??o positiva que indica a sua relev?ncia para a promo??o da aprendizagem significativa, a partir dos itens analisados

Les galaxies massives sont moins nombreuses que ce qui est attendu avec le modèle standard (le modèle Λ-CDM). Ceci ce traduit par une formation d’étoiles moins importante que prévue dans les galaxies. Pour expliquer celà, il est globalement accepté que des processus stoppent le formation d’étoiles. Pour les galaxies massives, ceci est expliqué par l’action des trous noirs supermassifs. En accrétant du gaz, le trou noir central produit de l’énergie et de l’impulsion. Quand l’accrétion devient importante, le trou noir forme un noyau actif de galaxie, et l’énergie peut ralentir la formation d’étoiles, par chauffage du gaz, de la turbulence, ou par ablation du gaz (feedback négatif). Cependant, il existe des cas de feedback positif qui favorise la formation d’étoiles en comprimant le gaz. En particulier, une partie des noyaux actifs produisent des jets de plasma qui sont observés en émission radio. Ces jets radio peuvent intéragir avec du gaz le long de leur direction de propagation. Des telles interactions sont susceptibles de déclencher de la formation d’étoiles (formation induite par les jets). Ma thèse porte sur les interactions jet-gaz dans des radio galaxies proches. J’ai étudié l’effet du jet sur l’efficacité de la formation d’étoiles pour des interactions à des échelles globales (quelques kiloparsecs) et intermédiaires (quelques centaines de parsecs). Pour celà, j’ai observé et cartographié le gaz moléculaire, qui est un élément clé de la formation d’étoiles. Cette phase froide est observable grâce aux équipements au sol actuels de radio astronomie, comme ALMA, APEX, NOEMA et le 30m de l’IRAM. / Massive galaxies are less abundant than predicted by the standard model of galaxy formation (the Λ-CDM model). This means that galaxies form less stars than expected. To explain this behaviour, it is commonly accepted that some processes are at play and quench star formation. For massive galaxies, it is explained by the feedback of the supermassive black holes. While accreting gas, the central black hole produces energy and momentum. When gas accretion becomes important, the black hole forms an active galactic nucleus, and the energy is expected to quench star formation, via gas heating, turbulence or gas removal (negative feedback). However, evidence is found of so-called AGN positive feedback that favours star formation by compressing the gas. In particular, a fraction of the AGN population produces jets of plasma that are observed in radio emission. These radio jets may interact with gas that is located along the direction of propagation. Such interactions are invoked to trigger star formation (jet-induced star formation). My PhD focused on the jet-gas interaction for nearby radio galaxies. I explored the effect of the jet on the star formation efficiency in such interactions at global (few kiloparsecs) and intermediate (few hundreds parsecs) scales. To do so, I searched and mapped the molecular gas (via CO emission lines) that is a key ingredient for star formation. This cold gas is observable using current radio astronomy ground-based facilities, like ALMA, APEX, NOEMA and the 30m telescope.

Radio astronomy is used to study stars, galaxies, black holes and gas clouds radiation at radio frequencies. Detecting extremely weak signals from deep space radio sources requires high sensitive feed system associated with large dish antennas. The key figure of merit is survey speed, or the time required to map a region of the sky to a given source flux density. Survey speed is proportional to the frequency bandwidth, the field of view or observable region of the sky, and the squared sensitivity, where sensitivity is related to reflector aperture efficiency and system noise temperature. Compared to the traditional single feed, phased array feeds with significantly expanded field of view are considered as the next generation feed for radio telescope. This dissertation outlines the design, analysis and measurement of high sensitivity L-band and mm-wave phased array feeds for the 100-meter Green Bank Telescope. Theoretical works for radio astronomy includes design guideline for high sensitivity phased array feed, fundamental frequency bandwidth limit, array antenna loss influenced by mutual coupling and beamformer coefficients and possibility of superdirectivity for radio telescopes and other antennas. These study are helpful to understand and guide the design of a phased array feed system. In the absence of dish antennas, sparse phased arrays with aperiodic structure have been developed for satellite communications. A compromise between the peak side lobe level, array element density, directivity and design complexity is studied. We have found that the array peak side lobe level can be reduced by enhancing the array element direction at the main lobe direction, increasing the array element density and enlarging the array size. A Poynting streamline approach develops to understand the properties of a receiving antenna and the mutual coupling effects between array elements. This method has been successfully used to generate effective area shape for many types of antennas and guide the design of a superdirective antenna. Motivated by this method, a superdirective antenna is experimental demonstrated.