PhD ceremony: Mr. J.D. Bregman, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen
Dissertation: System design and wide-field imaging aspects of synthesis arrays with phased array stations. To the next generation of SKA system designers
Promotor(s): prof. W.N. Brouw, prof. H.R. Butcher
Faculty: Mathematics and Natural Sciences
This dissertation covers the art of designing an aperture synthesis radio telescope like LOFAR. Well-known design principles are combined with a vision of new solutions that are expected to materialize in the near future, due to current technological developments. The central question is how scientific users with a given budget can achieve optimum results when the final instrument becomes operational.
System design starts with an analysis of the fundamental limitations of image forming by means of aperture synthesis, and of practical limitations like the disturbance caused by the ionosphere. Such an analysis leads to the formulation of a number of scaling laws for the optimum array configuration, and for the amount of digital processing that will be required.
An aperture synthesis telescope consists of an array of stations (groups of antennas). In a station, the signals from multiple antennas are added electronically in such a way that the sensitivity is maximized in a given direction. This technology offers the flexibility of distributing a given number of antennas over an optimum number of stations.
Our research has shown that such stations must have a minimum size, to allow effective correction of ionospheric disturbances over the entire field of view. Too small stations only allow proper correction for a limited part of their large field of view. Too few stations cause additional noise that can only partly be removed by more processing.
An important practical problem is the non-trivial amount of processing that is required for image forming. Therefore, an important result of this thesis is the development of new and efficient methods, that reduce the required processing to the theoretical minimum, i.e. proportional to the area of the field of view, expressed in resolution elements. For a sufficient number of stations in an optimal configuration, it should be possible to achieve minimum noise as well as minimum processing for the new generation of giant radio telescopes, from LOFAR to SKA and beyond.
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