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Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna
Thesis (MEng)--Stellenbosch University, 2018.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2018
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| _version_ | 1867614016689405952 |
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| access_status_str | Open Access |
| author | Louw, Ridalise |
| author2 | De Villiers, D. I. L. |
| author_browse | De Villiers, D. I. L. Louw, Ridalise |
| author_facet | De Villiers, D. I. L. Louw, Ridalise |
| author_sort | Louw, Ridalise |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2018. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/103556 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:45:20.375Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2018 |
| publishDateRange | 2018 |
| publishDateSort | 2018 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/103556 Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna Louw, Ridalise De Villiers, D. I. L. Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. Broadband networks -- Metrics UCTD Antennas, Reflector Surrogate-based optimization Feeds, Antenna Thesis (MEng)--Stellenbosch University, 2018. ENGLISH ABSTRACT: The focus of this thesis is on a design methodology for a pyramidal sinuous antenna for use as a wideband feed in the SKA reflector antenna system. The design objective is to maximise the receiving sensitivity of the feed, while maintaining a reflection coefficient of at most -10 dB over the entire band. Acquiring accurate solutions of the antenna’s performance metrics for each geometric variation in the design space requires a full wave solution for each possibility. This is a time consuming task. Thus, the focus in this thesis is on finding accurate surrogate models that are fast to evaluate, on which the design can be done. Surrogate models require the availability of a coarse model that is less accurate, but faster to evaluate than the fine model. Truncated models of the antenna structure that operate at the band edges of the full fine model are used. These provide a good approximation of the behaviour of the pyramidal sinuous antenna. A simple surrogate model is suggested for the sensitivity of the system, which makes use of an output space mapping technique where a second-order polynomial regression term is applied to the difference between the sensitivity of the coarse and fine models, using only a few fine model evaluations. A rational interpolation model is used to find the input impedance of the antenna from which the reflection coefficient is calculated. Rational interpolation of high-fidelity data, acquired from the fine model, is done first. Low-fidelity data, acquired from the coarse model, are subsequently added to the rational interpolant so as to improve the accuracy of the model without the need for adding additional high-fidelity data points. The constraint which ensures a pole-free rational interpolant restricts the solution of the model. This leads to the introduction of a blended rational interpolation method that locally models the trend of the low-fidelity data and is then blended together into a global interpolant using quadratic B-spline functions. A comparison of this model to other interpolation methods shows this blended rational interpolant to perform well. Brief consideration is given to the application of these surrogate modelling methods on a 5:1 bandwidth pyramidal sinuous antenna. This example illustrates the significant speed-up that is achieved for the design, where a speed-up factor close to 16 is achieved. The design of a 3:1 bandwidth is then considered with two geometric parameters as input to the design. Using very few high-fidelity data points, the blended rational interpolation method leads to a predicted region of where the reflection coefficient is less than -10 dB that has an 11.9% error. From this region, the antenna with the maximum sensitivity is identified, with the surrogate predicting an average sensitivity of 3:651 m2=K. Validation of the results shows the average sensitivity to be equal to 3:7139 m2=K and a reflection coefficient below -10.52 dB over the entire band. AFRIKAANSE OPSOMMING: Die fokus in hierdie tesis is op die ontwerp van ’n piramidiese siniese antenna vir gebruik as ’n wyeband voer in die SKA weerkaatsingsantenna. Die mikpunt vir die ontwerp is om die ontvangersensitiwiteit van die voer te maksimeer, terwyl daar gelyktydig aan ’n maksimum weerkaatskoëffisiënt van -10 dB oor die hele band voldoen word. Om akkurate oplossings van die antenna se werksverrigtingsmaatstawwe vir elke geometriese variasie in die ontwerpsruimte te bekom, word volgolf simulasies vir elke moontlikheid verlang. Hierdie is ’n tydrowende proses. Daarom fokus hierdie tesis daarop om akkurate surrogaatmodelle te bou wat vinnig is om te evalueer en waarop die ontwerp dan gedoen kan word. Surrogaatmodelle verlang die beskikbaarheid van ’n growwe model wat minder akkuraat is as die fyn model, maar wat vinnig is om te evalueer. Afgesnyde modelle van die antenna struktuur wat werkend is op die rante van die frekwensiebande van die volle fyn model word gebruik. Hierdie modelle gee ’n goeie afskatting van die gedrag van die piramidiese siniese antenna. ’n Eenvoudige surrogaatmodel word voorgestel vir die sensitiwiteit van die stelsel, wat gebruik maak van ’n afvoerruimtekartering tegniek waar ’n tweede-orde polinomiese regressieterm verkry is op die verskil tussen die sensitiwiteit van die growwe en fyn modelle, deur van net ’n paar fyn model evaluasies gebruik te maak. A rasionele interpolasie model word gebruik om die intree impedansie van die antenna te vind, waarvan die weerkaatskoëffisiënt bereken word. Eerste word rasionele interpolasie van hoë-getrouheid data wat van die fyn model afkomsitg is gedoen. Dan word laë-getrouheid data by die interpolant gevoeg sodat die akkuraatheid van die model verbeter word sonder om addisionele hoë-getrouheid datapunte by te voeg. Die beperking wat toegepas word om te verseker dat die model nie pole bevat nie, perk die oplossing van die model in. Dit lei na die bekendstelling van ’n gemengde rasionele interpolasie metode wat plaaslik die tendens van die laë-getrouheid data modelleer en dan saamgemeng word in ’n globale interpolant deur middel van kwadratiese B-spline funksies. ’n Vergelyking van hierdie model met ander interpolasiemetodes wys dat hierdie gemengde rasionele interpolant goed werk. Die aanwending van hierdie surrogaatmodelle op ’n 5:1 bandwydte piramidiese siniese antenna word kortliks oorweeg. Hierdie voorbeeld illustreer die merkwaardige versnelling wat verkry word vir die ontwerp, met ’n tydsbesparingsfaktor naby aan 16. Die ontwerp van ’n 3:1 bandwydte piramiede siniese antenna word oorweeg met twee geometriese parameters as intreë tot die ontwerp. Deur van net ’n paar hoë-getrouheid datapunte gebruik te maak, voorspel die gemengde rasionele interpolant ’n area waar die weerkaatskoëffisiënt onder -10 dB is met ’n 11.9% fout. Uit hierdie area word die antenna met die maksimum sensitiwiteit geïdentifiseer en die surrogaatmodel voorspel die sensitiwiteit by hierdie punt as gemiddeld 3:651 m2=K. Validasie van die resultate wys dat die sensitiweit gelyk is aan ’n gemiddeld van 3:7139 m2=K en dat die weerkaatskoëffisiënt oor die hele bandwydte onder -10.52 dB is. 2018-02-20T08:52:21Z 2018-04-09T07:00:34Z 2018-02-20T08:52:21Z 2018-04-09T07:00:34Z 2018-03 Thesis http://hdl.handle.net/10019.1/103556 en_ZA Stellenbosch University 140 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Broadband networks -- Metrics UCTD Antennas, Reflector Surrogate-based optimization Feeds, Antenna Louw, Ridalise Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title | Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title_full | Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title_fullStr | Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title_full_unstemmed | Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title_short | Surrogate modelling of performance metrics of a wideband feed for the SKA reflector antenna |
| title_sort | surrogate modelling of performance metrics of a wideband feed for the ska reflector antenna |
| topic | Broadband networks -- Metrics UCTD Antennas, Reflector Surrogate-based optimization Feeds, Antenna |
| url | http://hdl.handle.net/10019.1/103556 |
| work_keys_str_mv | AT louwridalise surrogatemodellingofperformancemetricsofawidebandfeedfortheskareflectorantenna |