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Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments
Pieterse, C. M. 2025. Antenna Beam Pattern Modelling for Sky-Averaged 21 cm Cosmology Experiments. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/96772db0-0099-4d73-885b-ef453a8bb8df
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| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613967297282048 |
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| access_status_str | Open Access |
| author | Pieterse, Carla Maria |
| author2 | De Villiers, D. I. L. |
| author_browse | De Villiers, D. I. L. Pieterse, Carla Maria |
| author_facet | De Villiers, D. I. L. Pieterse, Carla Maria |
| author_sort | Pieterse, Carla Maria |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Pieterse, C. M. 2025. Antenna Beam Pattern Modelling for Sky-Averaged 21 cm Cosmology Experiments. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/96772db0-0099-4d73-885b-ef453a8bb8df |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132264 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:33.029Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132264 Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments Pieterse, Carla Maria De Villiers, D. I. L. Stellenbosch University. Faculty of Engineering. Dept. of Electrical & Electronic Engineering. Antenna radiation patterns Broadband communication systems Radio astronomy Microwave antenna arrays -- Mathematical models UCTD Pieterse, C. M. 2025. Antenna Beam Pattern Modelling for Sky-Averaged 21 cm Cosmology Experiments. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/96772db0-0099-4d73-885b-ef453a8bb8df Thesis (PhD)--Stellenbosch University, 2025. ENGLISH ABSTRACT: Detection of the sky-averaged neutral hydrogen 21 cm signal with a wideband antenna operating at meter wavelengths enables astronomers to investigate the thermal history of the Universe and processes that govern the formation of the first stars and g alaxies. However, this measurement poses significant challenges because the foreground is vastly brighter than the cosmological signal and must be first accurately modelled and subtracted from the data. The Radio Experiment for the Analysis of Cosmic Hydrogen (REACH seeks to improve this process by simultaneously fitting the complete posterior distribution of both the cosmological and foreground signals using Bayesian inference. However, this approach depends on an informed prior, which is partly derived from a simulated antenna power pattern. Uncertainty in the antenna power pattern can stem from various sources that are difficult to model and can lead to discrepancies between the true antenna beam and the models used in this analysis, hindering the accurate recovery of the 21 cm signal. This study focuses specifically on uncertainties resulting from geometric perturbations that can be due to real-world variabilities, such as mechanical tolerances and thermal expansion. To address this challenge, a parameterising technique of the antenna power beam is proposed to simplify and compress the representation of its characteristics, enhancing adaptability to account for geometric perturbations. This parameterised method can then be incorporated into Bayesian inference as a model that can be fitted for. The effects of the power beam uncertainty are not well understood. To address this issue, we conduct a forward modelling investigation using mock data with varying levels of power pattern uncertainty within the REACH pipeline. We create perturbed antenna power patterns by truncating a singular-value-decomposed simulated power pattern, using one version to generate mock observation data and the other to inform the prior. The power pattern uncertainty is quantified as Δ𝐷, representing the absolute mean difference between the original and perturbed power patterns. Our analysis reveals that a Δ𝐷, better than −35 dB, corresponding to sub-millimeter-level accuracy in the antenna’s dimensions, is essential for confidently detecting the global signal. Furthermore, a strategy for leveraging in-field measurements, specifically S11 scattering parameters, to inform geometric perturbation in the antenna beam patterns is introduced. The test results suggest that the antenna patterns derived from the method can reduce uncertainty by up to ∼ 10 dB when compared against nominal antenna patterns with no assumed perturbations. AFRIKAANSE OPSOMMING: ’n Waarneming van die ruimtelik-gemiddelde neutrale waterstof 21 cm sein met ’n wyeband antenna wat rondom meter golflengtes werk, sou sterrekundiges in staat stel om die termiese geskiedenis van die heelal en die prosesse wat die vorming van die eerste sterre en sterrestelsels bepaal, te ondersoek. Hierdie meting is egter ‘n aansienlike uitdaging aangesien die voorgrond baie helderder is as die kosmologiese sein, en eers akkuraat gemodelleer moet word en dan van die data afgetrek moet word. Die Radio-eksperiment vir die Analise van Kosmiese Waterstof (REACH poog om hierdie proses te verbeter deur gelyktydig die volledige posterior verspreiding van beide die kosmologiese en voorgrond seine te vergelyk deur ‘n Bayesiese afleiding. Hierdie benadering is egter afhanklik van ’n ingeligte voorafgaande, wat gedeeltelik afgelei word van ’n gesimuleerde antenna-stralingspatroon. Onsekerheid in die antennastralingspatroon kan veroorsaak word deur verskeie oorsake, wat moeilik is om te modelleer, en dit kan lei tot verskille tussen die ware antennapatroon en die modelle wat in die analise gebruik word; wat die akkurate bepaling van die 21 cm-sein belemmer. Hierdie studie fokus spesifiek op onsekerhede wat voortspruit uit geometriese versteurings wat te wyte kan wees aan veranderlikes in fisiese werklikhede soos meganiese toleransies en termiese uitsetting. Om hierdie uitdaging aan te spreek, word ’n parameteriseringstegniek voorgestel, van die antenna-stralingspatroon, deur die voorstelling van die patroon se kenmerke te ereenvoudig en saam te pers, en sodoende die vergelykbaarheid te verbeter deur geometriese versteurings in berekening te bring. Hierdie geparameteriseerde metode kan dan in ‘n Bayesiaanse inferensie geïnkorporeer word as ’n vergelykbare model. Die invloed van stralingspatroon-onsekerheid is onduidelik. Hierdie kwessie word aangespreek deur ’n voorwaartse modelleringsondersoek wat gebruik maak van skyndata met verskillende vlakke van stralingspatroononsekerhede binne die REACH-pyplyn. ‘n Versteurde stel antenna-stralingspatrone word geskep deur ’n enkelwaarde-ontbinde gesimuleerde stralingspatroon te skei, en voorts een weergawe te gebruik om skynwaarnemingsdata te genereer terwyl die res die vorafgaande verspreiding inlig. Die stralingspatroononsekerheid word gekwantifiseer as Δ𝐷, wat die absolute gemiddelde verskil tussen die oorspronklike en versteurde stralingspatrone verteenwoordig. Die ontleding onthul dat ’n Δ𝐷, beter as -35 dB, wat ooreenstem met sub-millimeter-vlak akkuraatheid in die antenna se afmetings, noodsaaklik is om die globale sein met selfvertroue op te spoor. Verder word ’n strategie vir die gebruik van in-veld metings, spesifiek S11 van die strooiparameters, voorgestel om meetkundige versteurings in die antennapatrone uit te lig. Die toetsresultate dui daarop dat die antennapatrone wat deur die metode verkry word, onsekerheid met tot ∼ 10 dB kan verminder wanneer dit vergelyk word met nominale antennapatrone met geen versteurings nie. Doctoral 2025-06-02T07:48:56Z 2025-06-02T07:48:56Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132264 en Stellenbosch University xii, 112 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Antenna radiation patterns Broadband communication systems Radio astronomy Microwave antenna arrays -- Mathematical models UCTD Pieterse, Carla Maria Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title | Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title_full | Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title_fullStr | Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title_full_unstemmed | Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title_short | Antenna beam pattern modelling for sky-averaged 21 cm cosmology experiments |
| title_sort | antenna beam pattern modelling for sky averaged 21 cm cosmology experiments |
| topic | Antenna radiation patterns Broadband communication systems Radio astronomy Microwave antenna arrays -- Mathematical models UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132264 |
| work_keys_str_mv | AT pietersecarlamaria antennabeampatternmodellingforskyaveraged21cmcosmologyexperiments |