Lightning protection and radio frequency interference mitigation for the Karoo Array Telescope

• Main Author: Wiid, P. Gideon
• Other Authors: Reader, H. C.
• Format: Others
• Language: en
• Published: Stellenbosch : University of Stellenbosch 2010
• Subjects: Telescopes > Lightning protection; RFI mitigation; Computational modelling; RFI measurements; Dissertations > Electronic engineering; Theses > Electronic engineering; Telescopes > South Africa; Karoo Array Telescope (KAT or MeerKAT); Large astronomical telescopes > South Africa; Square Kilometre Array (SKA); Radio > Interference
• Online Access: http://hdl.handle.net/10019.1/4009

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. === ENGLISH ABSTRACT: South Africa and Australia are now the two remaining countries bidding for the Square Kilometre Array (SKA), the biggest and most sensitive project ever undertaken in radio astronomy. The South African SKA is demonstrating its technology capabilities through the Karoo Array Telescope (KAT or MeerKAT). The development of KAT is taking place in stages to optimise design and minimise risks at each stage. An array of seven 12 m antennas will be complete by the end of 2009, called KAT-7. The following phase will see the construction of MeerKAT, which will lead to eighty arrayed dishes. Lightning and RFI studies for KAT-7 are the focus of this dissertation. Due to the extent and complexity of the South African demonstrator project, these studies have largely been conducted on a single structure. Parameters for the dish antenna and pedestal design changed throughout their development. To be effective, the doctoral research had to track these changes appropriately. A Method of Moments frequency domain computational electromagnetic code, FEKO, is used throughout the study. The consequences of direct and indirect lightning strikes are examined for the KAT-7 structure. Important FEKO model verification is achieved through measurement of physical scale models in an anechoic chamber. The microwave simulation code, CST, gives direct comparison of FEKO results by using a finite volume time domain method of calculation. Using frequency domain analysis on these models, the lightning down conductor design over the dish antenna bearings is optimised with cost-effectiveness as one driving parameter. RFI coupling levels for different designs are compared to each other to identify areas requiring RFI mitigation. Analysis of resonances enables evaluation of the mitigation at frequencies sensitive to radio astronomy. A Sommerfeld integral ground plane is used together with the computational model to investigate the use of the concrete foundation steel reinforcing as part of the lightning earthing electrode system. Different interconnections of the steel reinforcing elements are critically evaluated. The KAT-7 design incorporated clear lightning protection and RFI mitigation policies derived from recommendations contained within this dissertation. === AFRIKAANSE OPSOMMING: Suid-Afrika en Australie is nou die oorblywende twee lande wat bie vir die Vierkante Kilometer Reeks (SKA), die grootste en mees sensitiewe projek nog ooit in radio astronomie onderneem. Die Suid Afrikaanse SKA demonstreer sy tegnologiese bekwaamheid met die Karoo Reeks Teleskoop (KAT of MeerKAT). Die ontwikkeling van KAT vind plaas in fases om die ontwerp te optimaliseer en risikos te minimaliseer met elke fase. ’n Reeks van sewe 12 m antennas, genaamd KAT-7, sal teen die einde van 2009 klaar wees. Die volgende fase behels die konstruksie van MeerKAT, wat sal lei tot ’n tagtig-skottel reeks. Die fokus van hierdie proefskrif hanteer weerlig en radiofrekwensie steurings (RFS) vir KAT-7. As gevolg van die omvang en kompleksiteit van die Suid-Afrikaanse demonstreerder projek, is die studies hoofsaaklik op een struktuur gedoen. Parameters vir die antenna-skottel en -voetstuk ontwerp het met hul ontwikkeling deurgaans verander. Om effektief te wees, moes die doktorale navorsing hierdie veranderinge toepaslik volg. ’n Metode-van-Momente frekwensiedomein rekenaar elektromagnetiese kode, FEKO, is deurgaans met die studie gebruik. Die gevolge van direkte en indirekte weerligslae vir die KAT-7 struktuur is ondersoek. Belangrike FEKO model bevestiging is bereik met metings van skaalmodelle in ’n anego¨ıse kamer. Die mikrogolf-simulasie kode, CST, gee ’n direkte vergelyking met die FEKO resultate deur ’n eindige-volume-tyd-domein metode van berekening te gebruik. Met behulp van frekwensiedomein analise van hierdie modelle, is die weerligafleierontwerp oor die antenna-skottel laers ge-optimaliseer, met koste-effektiwiteit as een van die drywingsparameters. RFS koppelingsvlakke vir onderskeie ontwerpe is teen mekaar opgeweeg om areas te identifiseer wat RFS tempering benodig. Analise van resonansies stel die evaluering van die tempering in staat teen frekwensies wat sensitief is vir radio astronomie. ’n Sommerfeld integrale grondvlak word saam met die rekenaarmodel gebruik om die insluiting van die beton se staalversterking as deel van die aardingselektrodestelsel te ondersoek. Verskillende bindmetodes van die onderlinge staalversterkingselemente word krities ge¨evalueer. Die KAT-7 ontwerp inkorporeer duidelike weerligbeveiligings- en RFS temperingstrategie ¨e, komende van aanbevelings in hierdie proefskrif omskryf