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1. Young, Andre. Improving the direction-dependent gain calibration of reflector antenna radio telescopes.
Degree: PhD, Electrical and Electronic Engineering, 2013, Stellenbosch University
ENGLISH ABSTRACT: Utilising future radio interferometer arrays, such as the Square Kilometre Array (SKA), to their full potential will require calibrating for various direction- dependent effects, including the radiation pattern (or primary beam in the parlance of radio astronomers) of each of the antennas in such an array. This requires an accurate characterisation of the radiation patterns at the time of observation, as changing operating conditions may cause substantial variation in these patterns. Furthermore, fundamental imaging limits, as well as practical time constraints, limit the amount of measurement data that can be used to perform such characterisation. Herein three techniques are presented which aim to address this requirement by providing pattern models that use the least amount of measurement data for an accurate characterisation of the radiation pattern. These methods are demonstrated through application to the MeerKAT Offset Gregorian (OG) dual-reflector antenna. The first technique is based on a novel application of the Jaco bi-Bessel series in which the expansion coefficients are solved directly from the secondary pattern. Improving the efficiency of this model in the desired application leads to the development of a different set of basis functions, as well as two constrained solution approaches which reduce the number of pattern measurements required to yield an accurate and unique solution. The second approach extends the application of the recently proposed Characteristic Basis Function Patterns (CBFPs) to compensate for non-linear pattern variations resulting from mechanical deformations in a reflector antenna system. The superior modelling capabilities of these numerical basis functions, which contain most of the pattern features of the given antenna design in a single term, over that of analytic basis functions are demonstrated. The final method focusses on an antenna employing a Phased Array Feed (PAF) in which multiple beam patterns are created through th e use of a beam-former. Calibration of such systems poses a difficult problem as the radiation pattern shape is susceptible to gain variations. Here we propose a solution which is based on using a Linearly Constrained Minimum Varia nce (LCMV) beamformer to conform the realised beam pattern to a physics-based analytic function. Results show that the LCMV beamformer successful ly produces circularly symmetric beams that are accurately characterised with a single-term analytic function over a wide FoV.
AFRIKAANSE OPSOMMING: Die volle benutting van toekomstige radio interferometersamestellings, soos die Square Kilometre Array (SKA), benodig die kalibrering van verskeie rigting-afhanklike effekte, insluitend die stralingspatroon (bekend as die primêre bundel onder radio astronome) van elke antenne in só ’n samestelling. Hierdie benodig ’n akkurate karakterisering van die stralingspatrone op die waarnemingstydstip, aangesien veranderende bedryfskarakteristieke ’n beduidende afwyking in hierdie patrone veroorsaak. Verder,…Advisors/Committee Members: Davidson, D. B., Maaskant, R., Ivashina, M. V., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering..
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APA (6th Edition):
Young, A. (2013). Improving the direction-dependent gain calibration of reflector antenna radio telescopes. (Doctoral Dissertation). Stellenbosch University. Retrieved from http://hdl.handle.net/10019.1/80915
Chicago Manual of Style (16th Edition):
Young, Andre. “Improving the direction-dependent gain calibration of reflector antenna radio telescopes.” 2013. Doctoral Dissertation, Stellenbosch University. Accessed October 14, 2019. http://hdl.handle.net/10019.1/80915.
MLA Handbook (7th Edition):
Young, Andre. “Improving the direction-dependent gain calibration of reflector antenna radio telescopes.” 2013. Web. 14 Oct 2019.
Young A. Improving the direction-dependent gain calibration of reflector antenna radio telescopes. [Internet] [Doctoral dissertation]. Stellenbosch University; 2013. [cited 2019 Oct 14]. Available from: http://hdl.handle.net/10019.1/80915.
Council of Science Editors:
Young A. Improving the direction-dependent gain calibration of reflector antenna radio telescopes. [Doctoral Dissertation]. Stellenbosch University; 2013. Available from: http://hdl.handle.net/10019.1/80915