Investigation and characterization of the HERA dish and feed using electromagnetic simulations

Venter, Mariet (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: This thesis presents the results of the electromagnetic analysis of the dish and feed for the Hydrogen Epoch of Reionization Array (HERA) experiment. The science goal for HERA is a challenging task in the form of detecting and characterizing the power spectrum of the Epoch of Reionization (EoR). The HERA faceted parabolic dish is investigated where it is determined that, at the relevant frequencies, the panels forming the dish is not a significant deviation from a perfect paraboloid. However, the screen placed on the dish does cause variations in the gain across frequency. The mutual coupling between several HERA elements is determined not to be significant even without including the screen. Furthermore, at 150 MHz it is found that the HERA dish delivers a Field of View of approximately 9˚ and sidelobe levels of 15 dB below the main beam, which has a gain of 25 dB. The beam level at the horizon is measured at approximately 40 dB below the main beam. The uv-coverage of HERA as an interferometer is calculated for a tight-packed hexagon configuration. With the inclusion of outlier elements, this coverage improves significantly and it is shown that HERA will have excellent imaging capabilities. The delay-spectrum technique used by HERA astronomers is unpacked and applied to the HERA dish using electromagnetic simulations and post-processing. It is determined that reflections off the dish does not meet the -60 dB power after 60 ns specification. Rather, these reflections are measured at -35 dB. Results from modelling and optimization in the frequency domain of alternative feeds for HERA is compared to the current PAPER feed. This includes several versions of the bowtie feed, a scaled PAPER feed and a sinuous feed, which is also manufactured and measured. It is shown that such an effort in conjunction with a reflector is met with challenges due to the low frequency band.

AFRIKAANSE OPSOMMING: Hierdie tesis lewer resultate van die elektromagnetiese ontleding van die Hydrogen Epoch of Reionization Array (HERA) eksperiment se skottel en voer. Die uitdagende wetenskapsdoel vir HERA is die opsporing en karakterisering van die Epog van Herionisasie (EoR) se drywing. Deur ’n ondersoek te doen van die HERA skottel, word dit bepaal dat die panele waaruit die skottel saamgestel is, nie ’n groot afwyking van ’n perfekte parabool veroorsaak nie. Die skerm bo-op die skottel veroorsaak wel variasies in die aanwins teenoor frekwensie. Die wedersydse-koppeling tussen ’n aantal HERA elemente het nie ’n groot invloed nie, selfs sonder die skerm. By 150 MHz word daar gevind dat die HERA skottel ’n sigveld van ongeveer 9˚ het en sy-lob vlakke van 15 dB minder as die hoofbundel, wat ’n aanwins van 25 dB het. Die drywingspatroon by die horison word gemeet by ongeveer 40 dB minder as die hoofbundel. Die uv-dekking van HERA word bereken vir ’n nou-verpakte seshoek konfigurasie. Met die insluiting van wydomliggende elemente, verbeter die uv-dekking aansienlik en word daar aangedui dat HERA uitstekende beeld-vermoëns sal hê. Die vertraging-spektrum tegniek wat gebruik word deur HERA sterrekundiges word ondersoek en toegepas op die HERA skottel met behulp van elektromagnetiese simulasies en post-verwerking. Dit word vasgestel dat weerkaatsings van die skottel nie voldoen aan die -60 dB seinsterkte na 60 ns spesifikasie nie. Inteendeel, die weerkaatsings word gemeet by -35 dB. Resultate van modellering en optimering in die frekwensiegebied van alternatiewe voere vir HERA word vergelyk met die huidige PAPER voer. Dit sluit verskeie weergawes van die strikdasvoer, ’n geskaalde PAPER voer en ’n kronkelende voer in, wat ook gebou en getoets is. Daar word aangetoon dat so ’n poging, in samewerking met ’n reflektor, uitdagend is as gevolg van die lae-frekwensie band.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98480
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