Efficient optimisation of wideband reflector feed antennas

Date
2021-03
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: This dissertation presents research work on the e cient optimisation of wideband re ector feed antennas for radio astronomy applications. The method maximises the receiving sensitivity of a radio telescope while ensuring that the feed re ection coe cient response satis es some prescribed criterion. Re ector feed antennas are geometrically complex structures which normally require several parameters to describe their form. This casts their optimisation as a high-dimensional design space problem. Furthermore, the antenna responses are di cult to predict and require electromagnetic simulations for their analysis. These responses are also non-linear and cannot be easily mapped to the input variable space. This results in the need for numerical optimisation techniques for their design. Due to the computational complexity associated with developing optimised radio telescopes, surrogate modelling is identi ed as an e cient optimisation technique that will accelerate the design of re ector feed antennas. The method allows for a parametric description of primary antenna responses the radiation pattern and re ection coe cient, as a function of the antenna geometry and operational parameters (frequency and angular variation). The feed antenna radiation pattern is e ciently approximated using the Characteristic Basis Function Pattern (CBFP) method. A probability-based formulation of the worst-case re ection coe cient response informs a penalty function that veri es whether a prescribed impedance criterion is violated. This gives insight into the re ection coe cient response across the geometric design space without the complex computation that is normally required to characterise this feature. A ray-tracing based method is developed to estimate the antenna noise temperature which allows for a rapid approximation of the receiving sensitivity. The described modelling techniques are then integrated into a multi- delity trust-region based optimisation framework, which is con gured to maximise the receiving sensitivity of wideband single pixel feed antennas in relatively high-dimensional design spaces. The e cacy of the framework is validated through a comparative study and a Quad-Ridged Flared Horn (QRFH) antenna is optimised for the SKA project's SKA1-MID Band A frequency band and candidate feeds are developed for the next-generation Very Large Array (ngVLA) program's Band 2 frequency band.
AFRIKAANSE OPSOMMING: Hierdie verhandeling bied navorsingswerk op die e ektiewe optimering van wyeband weerkaatsantennavoere vir radio sterrekunde toepassings. Die metode maksimeer die ontvanger sensitiwiteit van 'n radio teleskoop terwyl dit verseker dat die voer weerkaatskoe siënt weergawe voldoen aan een-of-ander voorgeskrewe vereiste. Weerkaatsantennavoere is geometriese komplekse strukture waarvan die vorm normaalweg deur verskeie parameters beskryf word. Dit veroorsaak dat optimering van hierdie strukture as 'n hoë-dimensionele ontwerpstaak beskou kan word. Verder is dit moeilik om die antenna gedrag te voorspel, en word elektromagnetiese simulasie verlang vir die analise daarvan. Hierdie gedrag is ook nie-lineêr en kan nie maklik na die intreeruimte karteer word nie. Vandaar die vereiste vir numeriese optimeringstegnieke vir die ontwerp van hierdie antennas. As gevolg van die berekeningskompleksiteit geassosieer met die ontwikkeling van geoptimeerde radio teleskope, word surrogaatmodellering identi seer as 'n e ektiewe optimeringstegniek wat die ontwerp van weerkaatsantennavoere sal versnel. Die metode laat 'n parametriese beskrywing van primêre antenna weergawes toe die stralingspatroon en weerkaatskoe siënt, as funksies van die antenna geometrie en operasionele parameters (frekwensie en hoek). Die voerantenna stralingspatroon word e ektief benader deur die karakteristieke basisfunksie-patroon metode. 'n Waarskynlikheid gebaseerde formulering van die slegste geval weerkaatskoe siënt weergawe voer 'n penaliseringsfunksie wat bevestig of 'n voorgeskrewe impedansie beperking oorskry word. Dit verskaf insig oor die weerkaatskoe siënt gedrag oor die geometriese ontwerpsruimte sonder die komplekse berekeninge wat normaalweg benodig word om hierdie eienskap te karakteriseer. 'n Straalvolg gebaseerde metode is ontwikkel om die antenna ruistemperatuur af te skat, wat toelaat dat 'n vinnige benadering vir die ontvanger sensitiwiteit bepaal kan word. Die modelleringstegnieke word dan in 'n multi-trou vertrouensgebied gebaseerde optimeringsraamwerk geïntegreer, wat opgestel word om die ontvanger sensitiwiteit van wyeband enkel pixel voer antennas te maksimeer in relatiewe hoë-dimensionele soekruimtes. Die werkverrigting van die raamwerk was bevestig deur 'n vergelykende studie, 'n gladde muur vier-rif horing was geoptimeer vir die SKA projek se SKA1-MID Band A frekwensieband, en kandidaatvoere vir die ngVLA program se Band2 frekwensieband was ontwerp.
Description
Thesis (PhD)--Stellenbosch University, 2021.
Keywords
Efficient Optimisation, UCTD, Wideband communication systems, Antennas, Reflector
Citation