Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Through the Karoo Array Telescope, and its extension MeerKAT, South Africa is demonstrating its capabilities to host the most powerful radio telescope ever, the Square Kilometre Array (SKA). This new interferometer is intended to assist radio astronomers in unlocking the mysteries concealed in the far regions of the universe. A thorough investigation of Radio Frequency Interference (RFI) sources at each stage of the design becomes relevant for the success of the project.
The electromagnetic coupling through coaxial cables is the main focus of this thesis
since 90% of the Electromagnetic Compatibility (EMC) problems come from inadequate
system layout and grounding, where cabling plays the major role. Interest revolves around
better noise immunity, low radiation and cost. Transfer impedance (ZT ) and shielding
e ectiveness (SE) are used as the cable selection criteria. Several measurements of coaxial
cables identi ed on KAT-7 have been performed for ZT characterisation from 300 kHz up to
1.3 GHz. A current injection method is used to identify the ZT for the low frequency region.
We derived the high frequency part of ZT , with a reverberation chamber technique (RC)
measuring shielding e ectiveness. At rst, we calibrated the RC according to the relevant
IEC 61000-4-21 standard and evaluated the result with an Open Area Test Site (OATS)
E- eld estimation. The accuracy of the E- eld within the chamber is also addressed, based
on statistical analysis of the chamber's independent samples.
The OATS E- eld equivalent determination showed a good correlation with the OATS
E- eld data of a standard radiator. A coaxial air-line ZT veri ed the theoretical ZT model
within 7 dB and showed the expected 20 dB/decade slope variation. Furthermore, the
braiding porpoising e ect has been noticed with some cable samples. Here, a variation less
than 20 dB/decade occurs at lower frequency. Then, the slope changes to 20 dB/decade
at high frequency. This study illustrates a practical comparison of cable performance and
constitutes a rst approach to RFI mitigation of the MeerKAT cabling system. / AFRIKAANSE OPSOMMING: Deur middel van die Karoo Reeks Teleskoop, asook sy uitbreiding MeerKAT, demonstreer Suid-Afrika sy vermo om die mees kragtige radioteleskoop ooit, die Vierkante Kilometer Reeks (SKA), te vestig. Hierdie nuwe interferometer is bedoel om radiosterrekundiges te
help in die ontsluiting van die geheimenisse wat versteek is in die verre reike van die heelal.
'n Deeglike ondersoek van Radio Frekwensie Steurings (RFS) bronne by elke stadium van
die ontwerp is belangrik vir die sukses van die projek.
Die elektromagnetiese koppeling deur koaksiale kabels is die hoo okus van hierdie tesis,
aangesien 90% van die elektromagnetiese versoenbaarheid (EMV) probleme ontstaan as
gevolg van onvoldoende stelsel-uitleg en beaarding, waar kabels die hoofrol speel. Beter
ruis-immuniteit, lae straling en koste vorm die areas van belang. Oordragimpedansie (ZT )
en afskermingsdoeltre endheid (SE) word gebruik as die kabelkeuringskriteria. Verskeie
metings van koaksiale kabels wat op KAT-7 gedenti seer is, is uitgevoer vir ZT karakterisering
van 300 kHz tot 1,3 GHz. 'n Stroom-induseringsmetode is gebruik om die ZT vir die
lae-frekwensiebereik te identi seer. Ons het die ho-frekwensie deel van ZT afgelei met 'n
weerkaatsingskamer tegniek (RC) wat afskermingsdoeltre endheid meet. Eerstens het ons
die RC gekalibreer volgens die relevante IEC 61000-4-21 standaard en die resultaat met
'n Ope Area Toetsterrein (OAT) E-veld benadering gevalueer. Die akkuraatheid van die
E-veld in die kamer is ook aangespreek, gebaseer op 'n statistiese analise van die kamer se
onafhanklike monsters.
Die OAT E-veld ekwivalente benadering het goed met die OAT E-veld data van 'n standaard
uistraler gekorreleer. 'n Koaksiale lugmedium-transmissielyn ZT bevestig die teoretiese ZT
model binne 7 dB en het ook die verwagte 20 dB/dekade variasie in helling getoon. Verder
is die golwende e ek oor die kabelomvlegting opgemerk met sekere kabels. Hier is 'n variasie
van minder as 20 dB/dekade gevind by die laer frekwensie. Dan verander die helling na
20 dB/dekade teen ho frekwensie. Hierdie studie toon 'n praktiese vergelyking van die
verrigting van die kabel en 'n eerste benadering tot RFS tempering van die MeerKAT
kabelstelsel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/18066 |
| Date | 12 1900 |
| Creators | Andriambeloson, Joely Andrianina |
| Contributors | Reader, H. C., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | Stellenbosch University |
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