Astronomy large-scale surveys require instrumentation to minimize the time required to complete observations of large sections of the sky. Optimizing receiver systems has been achieved through reducing the system temperature primarily by advances in low-noise amplifier technology to a point that the internally generated noise is now fast approaching the quantum limit. Instead, reflector-coupled focal plane arrays are now used to increase the field of view (FoV) by employing either multi-element horn feeds or phased array feeds. Widely spaced (2-3 wavelengths diameter) horn feeds inefficiently sample the available focal plane radiation, thus requiring multiple imaging passes. Alternatively, a more efficient method is to use a narrow element (0.5 wavelengths diameter) phased array feed with a beamformer to produce overlapping beams on the sky, fully Nyquist sampling the focal plane with a single pass. The FoV can be further increased with additional phased array feed (PAF) antenna-receiver modules adding to the contiguous fully sampled region. A 5 x 5 K-band (18 - 26 GHz) single polarization modular PAF incorporating an antenna array of planar axially symmetric elements is designed, simulated, manufactured and tested. Each narrow width tapered slot antenna element has an independent receiver chain consisting of a cryogenic packaged monolithic microwave integrated circuit (MMIC) GaAs amplifier and a packaged MMIC down converting mixer. Synthesized beams and beamformer characteristics are presented. The PAF imaging system performance is evaluated by survey speed and compared to the industry standard, the single pixel feed (SPF). Scientifically, K-band is attractive because it contains numerous molecular transitions, in particular the rotation-inversion lines of ammonia. These transitions are excited in dense gas, and can be used to directly measure kinetic temperatures and velocities of protostars throughout the Galaxy. Depending on the line detected, gas of different temperatures can be probed. It is concluded that even with a higher system temperature, a PAF with sufficient number of synthesized beams can outperform a SPF in imaging speed by more than an order of magnitude. / Graduate

The lunar Cherenkov technique is a promising method to resolve the mystery of the origin of the highest energy particles in nature, the ultra-high energy (UHE) cosmic rays. By pointing Earth-based radio-telescopes at the Moon to look for the characteristic nanosecond pulses of radio-waves produced when a UHE particle interacts in the Moon’s outer layers, either the cosmic rays (CR) themselves, or their elusive counterparts, the UHE neutrinos, may be detected. The LUNASKA collaboration aims to develop both the theory and practice of the lunar Cherenkov technique in order to utilise the full sensitivity of the next generation of giant radio telescope arrays in searching for these extreme particles. My PhD project, undertaken as part of the collaboration, explores three key aspects of the technique. In the first three chapters, I describe a Monte Carlo simulation I wrote to model the full range of lunar Cherenkov experiments. Using the code, I proceed to calculate the aperture to, and resulting limits on, a UHE neutrino flux from the Parkes lunar Cherenkov experiment, and to highlight a pre-existing discrepancy between existing simulation programs. An expanded version of the simulation is then used to determine the sensitivity of past and future lunar Cherenkov experiments to UHE neutrinos, and also the expected event rates for a range of models of UHE CR production. Limits on the aperture of the Square Kilometre Array (SKA) to UHE CR are also calculated. The directional dependence of both the instantaneous sensitivity and time-integrated exposure of the aforementioned experiments is also calculated. Combined, these results point the way towards an optimal way utilisation of a giant radio-array such as the SKA in detecting UHE particles. The next section describes my work towards developing accurate parameterisations of the coherent Cherenkov radiation produced by UHE showers as expected in the lunar regolith. I describe a ‘thinning’ algorithm which was implemented into a pre-existing electromagnetic shower code, and the extensive measures taken to check its veracity. Using the code, a new parameterisation for radiation from electromagnetic showers is developed, accurate for the first time up to UHE energies. The existence of secondary peaks in the radiation spectrum is predicted, and their significance for detection experiments discussed. Finally, I present the data analysis from three runs of LUNASKA’s on-going observation program at the Australia Telescope Compact Array (ATCA). The unusual nature of the experiment required both new methods and hardware to be developed, and I focus on the timing and sensitivity calibrations. The loss of sensitivity from finite-sampling of the electric field is modelled for the first time. Timing and dispersive constraints are used to determine that no pulses of lunar origin were detected, and I use my simulation software to calculate limits on an UHE neutrino flux from the experiment. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1371947 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009.

The lunar Cherenkov technique is a promising method to resolve the mystery of the origin of the highest energy particles in nature, the ultra-high energy (UHE) cosmic rays. By pointing Earth-based radio-telescopes at the Moon to look for the characteristic nanosecond pulses of radio-waves produced when a UHE particle interacts in the Moon’s outer layers, either the cosmic rays (CR) themselves, or their elusive counterparts, the UHE neutrinos, may be detected. The LUNASKA collaboration aims to develop both the theory and practice of the lunar Cherenkov technique in order to utilise the full sensitivity of the next generation of giant radio telescope arrays in searching for these extreme particles. My PhD project, undertaken as part of the collaboration, explores three key aspects of the technique. In the first three chapters, I describe a Monte Carlo simulation I wrote to model the full range of lunar Cherenkov experiments. Using the code, I proceed to calculate the aperture to, and resulting limits on, a UHE neutrino flux from the Parkes lunar Cherenkov experiment, and to highlight a pre-existing discrepancy between existing simulation programs. An expanded version of the simulation is then used to determine the sensitivity of past and future lunar Cherenkov experiments to UHE neutrinos, and also the expected event rates for a range of models of UHE CR production. Limits on the aperture of the Square Kilometre Array (SKA) to UHE CR are also calculated. The directional dependence of both the instantaneous sensitivity and time-integrated exposure of the aforementioned experiments is also calculated. Combined, these results point the way towards an optimal way utilisation of a giant radio-array such as the SKA in detecting UHE particles. The next section describes my work towards developing accurate parameterisations of the coherent Cherenkov radiation produced by UHE showers as expected in the lunar regolith. I describe a ‘thinning’ algorithm which was implemented into a pre-existing electromagnetic shower code, and the extensive measures taken to check its veracity. Using the code, a new parameterisation for radiation from electromagnetic showers is developed, accurate for the first time up to UHE energies. The existence of secondary peaks in the radiation spectrum is predicted, and their significance for detection experiments discussed. Finally, I present the data analysis from three runs of LUNASKA’s on-going observation program at the Australia Telescope Compact Array (ATCA). The unusual nature of the experiment required both new methods and hardware to be developed, and I focus on the timing and sensitivity calibrations. The loss of sensitivity from finite-sampling of the electric field is modelled for the first time. Timing and dispersive constraints are used to determine that no pulses of lunar origin were detected, and I use my simulation software to calculate limits on an UHE neutrino flux from the experiment. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1371947 / Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2009.

Thesis (doctoral)--Rijksuniversiteit Groningen, 2001. / "Stellingen" and errata slip inserted at front. Includes bibliographical references (p. 181-190. [Author's] Publications: p. 191-193).

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Beamforming is a technique used to combine signals from an array of antennas to effectively synthesize a single aperture and beam. In the Radio Astronomy community the technique is used to obtain a desirable beam pattern as well as to electronically point the beam of an array. Next generation radio telescopes such as the Square Kilometre Array (SKA) surpass current technology and will extensively make use of beamforming techniques. Various factors determine the output of a beamformer; however, given an array with a fixed configuration only the weights applied to the incoming signals affect the synthesized aperture and beam. Furthermore, the incoming data must be processed in real-time, at a rate equal to the input-output rate of the processor. Both the weighting function and the real-time implementation of beamforming, are the primary subjects of this thesis. In this thesis various deterministic weighting functions are investigated. The algorithms are implemented in a matlab program, serving as a simulation tool for investigating the techniques. The program is verified by comparing the expected theoretical outcomes to the simulated output. For the program the following functionalities are included: a steering technique, spectral weighting, Dolph-Chebychev, and the Least Square Error algorithm. Applications of these techniques is investigated and their prominence in the Radio Astronomy community is established. For the real-time beamformer implementation, the UniBoard platform configured with beamformer firmware, is investigated. This is important as the UniBoard is an excellent example of a beamformer implementation within the Radio Astronomy community. The architecture is used to emulate a linear array by implementing a python control script, where the output corresponded accurately with the expected theoretical values. The thesis also constitutes the design and implementation of a digital frequency domain beamformer on the ROACH board. This processing board is employed by the Karoo Array Telescope (KAT-7) in South Africa. This work is therefore important as it demonstrates a beamformer implementation on an architecture in use by the Radio Astronomy community. An antenna array is designed and built for the verification of the beamformer design. Results with a good degree of accuracy were obtained and where errors exist they are discussed. / AFRIKKANSE OPSOMMING: Bundelvorming is ’n tegniek waarmee die seine van ’n antenna samestelling gekombineer word om ’n enkele effektiewe stralingsvlak en stralingspatroon te sintiseer. In die Radio Astronomie gemeenskap word die tegniek gebruik om ’n gewenste stralingspatroon te sintiseer sowel as om die rigting van die patroon elektronies te beheer. Die Square Kilometre Array (SKA) is ’n toekomstige radioteleskoop en sal grootliks gebruik maak van bundelvorming tegnieke. Die uitset van bundelvormers word geaffekteer deur verskeie faktore, maar vir ’n gegewe samestelling is dit net die gewigsfunksies wat toegepas word op die inkomende seine wat die gesintiseerde patroon kan beheer. Verder moet die inkomende data verwerk word teen ’n tempo gelykstaande aan die inset-en-uitsetkoers van die verwerker. Die gewigsfunksie so wel as die implementasie van die bundelvormer is albei primêre onderwerpe van die tesis. ’n Verskeindenheid van deterministiese bundelvormingstegnieke sal ondersoek word in hierdie tesis. Die algoritmes is in ’n matlab program geïmplementeer vir simulasie doeleindes. Die program is geverifieër deur die uitset te vergelyk met die verwagte teoretiese waardes. Die program sluit die volgende funksies in: ’n rigting beheer algoritme, spektraalgewigte, Dolph-Chebychev, en die minste vierkantsfout algoritme. Hierdie tegnieke is van belang weens hul toepassing in die Radio Astronomie gemeenskap. Vir die implementasie van ’n bundelvormer is die UniBoard hardeware, geprogrameer in ’n bundelvormings modus, van gebruik gemaak. Hierdie aspek is belangrik omdat die Uni- Board ’n goeie voorbeeld van ’n geïmplementeerde bundelvormer in die Radio Astronomie gemeenskap is. Die UniBoard word gebruik om ’n lineêre samestelling te emuleer deur in python ’n beheer skrip te skryf, waar die uitset van die emuleerder akkuraat ooreenstem met die verwagte waardes. Die tesis behels ook die ontwerp en implementasie van ’n digitale frekwensiegebied bundelvormer op die ROACH platform. Hierdie verwerker word tans gebruik in die Karoo Array Telescope (KAT-7) in Suid-Afrika. Hierdie werk is dus belangrik omdat dit die implementasie van ’n bundelvormer op tegnologie wat huidiglik in die Radio Astronomie gemeenskap gebruik word demonstreer. Daarbenewens is ’n antenna samestelling ontwerp en gebou om die bundelvormer te verifieër. Die resultate is akkuraat tot ’n redelike mate. Waar daar ’n fout onstaan het word dit in die tesis bespreek.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Please refer to full text for abstract.

La radio astronomie étudie les sources cosmiques au travers de leur rayonnement dans le domaine radio. Les astronomes, utilisateurs passifs du spectre électromagnétique, ont à faire face à une pollution radio de plus en plus importante. Cette thèse s’intéresse particulièrement aux interférences radio d’origine humaine (RFI), et comment les observations radio astronomiques peuvent être réalisées en bandes de fréquences non-protégées. Les approches classiques consistent à contrôler les paramètres statistiques d’une observation. Une fois détectées, les données polluées sont retirées avant post-traitement. En plus d’autres avantages techniques par rapport aux radiotélescopes paraboliques classiques, les réseaux d’antennes offrent une information spatiale lors d’une observation astronomique. La diversité spatiale entre source cosmique d’intérêt (SCOI) et RFI peut être exploitée pour développer des traitements spatiaux d’interférences. Après la formulation d’un module de données multidimensionnel, une technique de soustraction de sous espace RFI est introduite. Cette technique consiste à soustraire la contribution des RFI aux données d’une observation. La projection orthogonale a déjà été considérée auparavant. Cependant, l’orthogonalité requise entre CSOI et RFI pour retrouver une source d’intérêt non biaisée ne peut vraisemblablement pas être satisfaite. Une approche basée sur une projection oblique est introduite afin de pallier à cette condition. Les techniques de projections sont comparées aux techniques classiques de beamforming en termes de réjection de l’interférence et de récupération de la source d’intérêt. Le sous-espace RFI est inconnu de manière générale et se doit d’être estimé. Plusieurs techniques permettant cette estimation, basées sur des propriétés statistiques des RFI et sources cosmiques, sont également présentées et comparées. Les différentes techniques ont été appliquées à des données astronomiques délivrées par le radio télescope Européen LOFAR. Enfin, une implémentation d’un algorithme de traitement spatial d’interférences sur le démonstrateur EMBRACE est présenté. / Radio astronomy studies cosmic sources through their radio emissions. As passive users, astronomers have to deal with an increasingly corrupted radio spectrum. The research presented here focuses on man-made Radio Frequency Interference (RFI), and how astronomical observations can be performed in non-protected frequency bands. Traditional approaches consist in monitoring radio telescopes output data through statistical parameters. Once detected, the corrupted data is removed before further processing. Besides other technical advantages compared to single dish radio telescopes, antenna arrays provide spatial information about astronomical observations. The spatial diversity between cosmic sources-of-interest (CSOI) and RFI can be exploited to develop spatial RFI processing. After formulating a multidimensional radio astronomical data model, an interference subspace subtraction technique is introduced. This approach consists in subtracting RFI contributions from antenna array radio telescopes data. Orthogonal projection applied to astronomical observation vector spaces has already been considered by the past. The orthogonality between RFI and CSOI subspaces is required to recover the CSOI without bias. In order to avoid this latter requirement, an oblique projection approach is here proposed. The projection techniques are compared to classic beamforming techniques in term of interference rejection and CSOI recovering. Being usually unknown, the RFI subspace has to be estimated. Several techniques allowing this estimation, based on statistical properties of RFI and cosmic sources (whiteness and cyclostationarity), are also presented and compared. The different techniques have been applied to real astronomical data, provided by the European radio telescope LOFAR. A last section presents an RFI mitigation algorithm implemented on the demonstrator EMBRACE.

abstract: The Cosmic Microwave Background (CMB) has provided precise information on the evolution of the Universe and the current cosmological paradigm. The CMB has not yet provided definitive information on the origin and strength of any primordial magnetic fields or how they affect the presence of magnetic fields observed throughout the cosmos. This work outlines an alternative method to investigating and identifying the presence of cosmic magnetic fields. This method searches for Faraday Rotation (FR) and specifically uses polarized CMB photons as back-light. I find that current generation CMB experiments may be not sensitive enough to detect FR but next generation experiments should be able to make highly significant detections. Identifying FR with the CMB will provide information on the component of magnetic fields along the line of sight of observation. The 21cm emission from the hyperfine splitting of neutral Hydrogen in the early universe is predicted to provide precise information about the formation and evolution of cosmic structure, complementing the wealth of knowledge gained from the CMB. 21cm cosmology is a relatively new field, and precise measurements of the Epoch of Reionization (EoR) have not yet been achieved. In this work I present 2σ upper limits on the power spectrum of 21cm fluctuations (Δ²(k)) probed at the cosmological wave number k from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) 64 element deployment. I find upper limits on Δ²(k) in the range 0.3 < k < 0.6 h/Mpc to be (650 mK)², (450 mK)², (390 mK)², (250 mK)², (280mK)², (250 mK)² at redshifts z = 10.87, 9.93, 8.91, 8.37, 8.13 and 7.48 respectively Building on the power spectrum analysis, I identify a major limiting factor in detecting the 21cm power spectrum. This work is concluded by outlining a metric to evaluate the predisposition of redshifted 21cm interferometers to foreground contamination in power spectrum estimation. This will help inform the construction of future arrays and enable high fidelity imaging and cross-correlation analysis with other high redshift cosmic probes like the CMB and other upcoming all sky surveys. I find future arrays with uniform (u,v) coverage and small spectral evolution of their response in the (u,v,f) cube can minimize foreground leakage while pursuing 21cm imaging. / Dissertation/Thesis / Doctoral Dissertation Physics 2018

This thesis outlines the design and implementation of a single channel, dual polarization pulsar timing instrument for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The new timer is designed to be an improved, temporary replacement for the existing device which has been in operation for over 20 years. The existing device is no longer reliable and is di±cult to maintain. The new pulsar timer is designed to provide improved functional- ity, higher sampling speed, greater pulse resolution, more °exibility and easier maintenance over the existing device. The new device is also designed to keeping changes to the observation system to a minimum until a full de-dispersion timer can be implemented at theobservatory. The design makes use of an 8-bit Reduced Instruction Set Computer (RISC) micro-processor with external Random Access Memory (RAM). The instrument includes an IEEE-488 subsystem for interfacing the pulsar timer to the observation computer system. The microcontroller software is written in assembler code to ensure optimal loop execution speed and deterministic code execution for the system. The design path is discussed and problems encountered during the design process are highlighted. Final testing of the new instrument indicates an improvement in the sam- pling rate of 13.6 times and a significant reduction in 60Hz interference over the existing instrument.

From abstract: Within the next few years a large number of new and vastly more sensitive radio astronomy facilities are scheduled to come online. These new facilities will map large areas of the sky to unprecedented depths and transform radio astronomy into the leading technique for investigating the complex processes which govern the formation and evolution of galaxies. This thesis combines multi-wavelength techniques, highly relevant to future deep radio surveys, to study the evolution and properties of faint radio sources. / TeX / Adobe Acrobat 9.54 Paper Capture Plug-in