Thermal analysis of a dense dipole array for the SKA Mid-frequency aperture array

Smale, Corey (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The Dense Dipole Array (DDA) has been designed as a candidate element for the Mid-Frequency Aperture Array that forms part of the SKA project. This is being developed to realise the aperture array concept in the mid-frequency range, which covers a band form roughly 400 to 1450 Mhz. The MFAA is highly anticipated with its incredible survey speed and is intended to be deployed in the Karoo of South Africa. The semi-desert region provides adequate spacing with the perfect radio quiet backdrop, but exposes the arrays to harsh climates. As the system noise temperature is dominated by the receiver noise in this frequency band, the environmental temperature can greatly influence the quality of received signals. This creates a challenge as the arrays will have to operate at ambient temperature as forced cooling cannot be implemented within reasonable cost and complexity, due to the large number of antennas. A thermal analysis is performed on the DDA to determine its suitability in the climate of the Karoo. This is done by developing and testing a finite element model that incorporates computational fluid dynamics to simulate the resulting temperatures of the DDA when in the extreme conditions of the Karoo. The primary component limiting the operating temperature of the DDA and the main consideration during the analysis is the integrated low-noise amplifier. Two operating parameters of the LNA, being the maximum temperature and change in temperature are evaluated to ensure the desired performance of the DDA is achieved and will therefore meet the requirements of the MFAA. It is found that a thermal solution is necessary to bring the DDA within acceptable operating conditions. An open enclosure is designed and optimised for this purpose that utilises a polypropylene cover to mitigate the effects of the environment while considering the impact on the electromagnetic performance. Further simulations are then performed to assess the degradation of antenna performance. In conclusion, the enclosure successfully reduces the operating parameters to an acceptable level, and the cover does have a minor impact on the electromagnetic performance although with foreseeable benefits in stabilization with further optimisation.

AFRIKAANSE OPSOMMING: Die Digte Dipool Samestelling (DDA) is ontwerp as 'n kandidaatelement vir die Midfrekwensie Apertuur Samestelling (MFAA) van die SKA. Dit word ontwikkel om die apertuur samestelling konsep, wat 'n frekwensiebereik van ongeveer 400 - 1450 MHz dek, te realiseer. Die MFAA word verwag om baie hoë opname spoed te kan lewer en is bedoel om die Karoo van Suid-Afrika gebou te word. Die semi-woestyn gebied verskaf genoeg ruimte met 'n stil radio agtergrond, maar stel die samestelling bloot aan die harde woestynklimaat. Aangesien die stelsel se sensitiwiteit gedomineer word deur die ontvanger se ruistemperatuur in hierdie frekwensieband, kan die omgewingstemperatuur 'n groot invloed h^e op die kwaliteit van die seine wat ontvang word. As gevolg van die groot hoeveelheid antennas word 'n uitdaging dus geskep aangesien die antennas by omgewingstemperatuur moet werk omdat dit nie prakties of koste-effektief is om die stelsel aktief te verkoel nie. 'n Termiese analise word dus uitgevoer om die geskiktheid van die DDA in die woestynklimaat te evalueer. Dit word vermag deur 'n eindige-element model wat berekeningsvloeistofdinamika gebruik om die termperature wat die DDA aan blootgestel sal word in die Karoo te ontwikkel en te toets. Die primêre component wat die toelaatbare werkstemperatuur van die DDA beperk, en dus die hoofoorweging van die analise is, is die geïntegreerde laeruis versterker (LNA). Twee werkstemperatuurkondisies van die LNA word ondersoek om die prestasie van die DDA te evalueer en om te bevestig of die vereistes van die MFAA nagekom word - die maksimum temperatuur, en die tempo van verandering in temperatuur. Daar is gevind dat 'n toepaslike termiese oplossing nodig is om die DDA binne aanvaarbare werkskondisies te hou. `n Oop omhulsel is ontwerp en geoptimeer hiervoor, en maak gebruik van 'n polipropileen deksel om die effek van die omgewing te versag. Die effek van die deksel om die elektromagnetiese prestasie is ook ge-evalueer om moontlike negatiewe effekte te identifiseer. Resulate toon dat die omhulsel die werkstemperatuur suksesvol verlaag het na aanvaarbare vlakke terwyl die effek op die samestelling se elektromagnetiese prestasie minimal was of selfs moontlik kan lei to verbetering in die stabiliteit van die impedansieaanpassing met verder optimering van die ontwerp van die samestelling.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105973
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