Modifed horn-type antennas for SKA RFI Monitoring

Thesis (MEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: Maintaining a site free of radio frequency interference (RFI) is an essential aspect in the performance of the Square Kilometre Array (SKA) radio telescope. Regular on-site RFI measurements have to be done to identify unwanted sources of RFI and to verify RFIcompliance of equipment within the operating frequencies of the telescope. To perform these measurements requires hyperband directional antennas that cover all the frequencies of the first phase of SKA-MID are required, ideally 200 MHz - 4 GHz, a bandwidth ratio of 20:1. In addition, they need to be mechanically robust and portable, since they often need to be mounted at a height for testing. For this application, we investigate three types of modified horn antennas: a doubleridged guide-horn (DRGH), a transverse electromagnetic (TEM) horn, and a Valentine antenna. These antennas are chosen because of their bandwidth and gain. A wideband coaxial to parallel-plate transition is also designed for feeding the Valentine and TEM horn antennas because of their symmetry. The three antennas are modelled, simulated in Dassault Systémes' CST Studio Suite and prototyped to analyse the complexity of construction and to compare measurement results with those simulated. The measured return loss, radiation patterns and gain results are a good replication of the simulated results. A surrogate-based optimization (SBO) scheme that uses Kriging model and Expected Improvement (EI) was used to optimize the antennas for return loss. Designing these structures using the normal supervised parametric sweeps is impractical due to the lengthy simulation times involved because of the wide bandwidth and large geometry. An SBO only requires a few full wave simulations of the structure to support the Kriging model, while each new simulation requested by the iterative process is selected at a position in the design space where the optimum solution is most likely, given the current estimation of the response. Using this technique, the return loss of the three antennas has been optimized and bandwidth ratio improved from 10 to 16. An analysis of the three antennas is done by comparing the fabrication process, the size, robustness and weight of the antennas, the ease of characterization and the performance of the antenna. Based on this analysis, the DRGH is recommended for RFI testing at the SKA radio telescope site.AFRIKAANSE OPSOMMING: Die instandhouding van 'n terrein vry van radiofrekwensie-steurings (RFS) is 'n wesenlike aspek in die uitvoering van die Vierkante Kilometer Reeks (SKA). Gereëlde RFS-metings moet op die terrein gedoen word om ongewenste bronne van RFS te identifiseer en om die RFS-nakoming van toerusting binne die gebruiksfrekwensies van die teleskoop te verifieer. Om hierdie metings uit te voer, verg dit hiperband gerigte antennas wat al die frekwensies van die eerste fase van SKA-MID dek, verkieslik 200 MHz - 4 GHz, 'n bandwydteverhouding van 20:1. Daarbenewens moet hulle meganies robuust en draagbaar wees, aangesien hulle dikwels op 'n hoogte gemonteer moet word vir toetse. Vir hierdie toepassing ondersoek ons drie soorte aangepaste horingantennas: 'n dubbelrygidshoring (DRGH), 'n transversale elektromagnetiese (TEM) horing en 'n Valentineantenna. Hierdie antennas word gekies as gevolg van hul bandwydte en wins. 'n Breëband koaksiale-na-parallelplaatoorgang is ook ontwerp vir die voer van die Valentine- en TEMhoringantennas vanweë hul simmetrie. Die drie antennas is gemodelleer, gesimuleer in Dassault Systemes CST Studio Suite en vervaardig om die kompleksiteit van konstruksie te ontleed en om die meetresultate met die gesimuleerde te vergelyk. Die gemete terugkeerverlies, stralingspatrone en aanwinsresultate is 'n goeie weerspieëling van die gesimuleerde resultate. 'n Surrogaat-gebaseerde optimisering (SBO)-skema met Krigingmodel en "Expected Improvement"(EI), is gebruik om die antennas se terugkeerverlies te optimiseer. Die ontwerp van hierdie strukture met behulp van die normaal bestuurde parametriese veeg is onprakties vanweë die lang simulasietye wat betrokke is as gevolg van die breë bandwydte en groot geometrie. 'n SBO benodig slegs 'n paar volledige-golf simu-lasies van die struktuur om die Kriging-model te ondersteun, terwyl elke nuwe simulasie wat deur die iteratiewe proses gevra word, gekies word op 'n plek in die ontwerpruimte waar die optimale oplossing waarskynlik is, gegewe die huidige beraming van die reaksie. Met behulp van hierdie tegniek is die terugkeerverlies van die drie antennas geoptimiseer en het die bandwydteverhouding van 10 tot 16 verbeter. 'n Analise van die drie antennas word gedoen deur die vervaardigings-proses, die grootte, robuustheid en gewig van die antennas, die gemak van karakterisering en die werkverrigting van die antenna te vergelyk. Op grond van hierdie ontleding word die DRGH aanbeveel vir RFS-toetsing op die SKA-radioteleskoopterrein.Master