Characterising the electromagnetic environment of MeerKAT

Phiri, Temwani Joshua (2017-03)

Thesis (PhD)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: MeerKAT is South Africa’s 64-dish precursor radio telescope to the Square Kilometre Array (SKA), currently under construction in the semi-desert Karoo region. As these are new generation instruments, their specifications far exceed those of existing telescopes and thereby increases their susceptibility to radio frequency interference (RFI). So far, much has been accomplished in terms of electromagnetic compatibility (EMC) interventions. However, surveys in the recent past have indicated the need to examine signal propagation in the Karoo in greater detail. In particular, reliable predictive tools are essential in order to fully characterize the environment which is changing gradually as infrastructure development progresses. As a matter of first importance, selected empirical propagation models were statistically assessed by comparison to measurements in the Karoo. Based on the root mean square error (RMSE) values, the transmission loss predictions were deemed reliable. In spite of this, the limitations of empirical modelling were apparent: failure to accurately model real ground, inability to incorporate scattering phenomena and inadequacy in representing underlying physical processes. To meet the accuracy demands of the South African SKA Project (SKA-SA) pertaining to characterising the complex environment of MeerKAT, a deterministic model exploiting full-wave and asymptotic techniques was developed. Referred to simply as a ray model, this solution utilised the method of moments (MoM) to determine antenna characteristics and solve for real ground, while physical optics was utilised to address scattering from the dishes. With the software FEKO as the interface and simulation engine, the MeerKAT core was reproduced computationally. Analysis of the numeric data revealed the full extent of electromagnetic complexity in relation to multipath. Most notably, high spatial resolution attenuation maps were generated, revealing high and low risk regions. This has benefits for identification of potential RFI problems. The ray model showed very good performance when examined against measurements (RMSE <4 dB). This is highly advantageous since numerical modelling allows a lot more flexibility than physical testing permits. In particular, the novelty and significance of this research is the ability to reproduce an actual deployment scenario with precision and high accuracy.

AFRIKAANSE OPSOMMING: Meerkat is Suid-Afrika se 64-skottel voorloper tot die Square Kilometre Array (SKA) radioteleskoop, wat tans in die semi-woestyn Karoo gebied gebou word. Omdat hierdie nuwe generasie instrumente is, oorskry hul spesifikasies dié van bestaande teleskope by verre, dus is hul vatbaarheid vir beide radiofrekwensie steurings (RFS) verhoog. Tot dusver is daar baie vermag in terme van elektromagnetiese versoenbaarheid (EMV) stappe. Onlangse opnames het egter gelei tot die behoefte aan verdere ondersoek van seinvoortplanting in die Karoo. In besonder is daar ’n behoefte aan betroubare voorspellingsgereedskap om ten volle die omgewing, wat geleidelik verander soos die ontwikkeling van infrastruktuur vorder, te karakteriseer. As ’n saak van eerste belang, is verkose empiriese voortplantingsmodelle statisties geëvalueer deur dit met metings in die Karoo te vergelyk. Op grond van die wortel-gemiddeld-kwadraatfout (WGKF) waardes, was die oordragverliesvoorspellings betroubaar. Ten spyte hiervan, was die beperkings van empiriese modellering duidelik: ware grond word nie akkuraat gemodelleer nie, verstrooiinsverskynsels word nie inkorporeer nie en onderliggende fisiese prosesse word nie voldoende voorgestel nie.. Om aan die akkuraatheid te voldoen wat van die Suid-Afrikaanse SKA Projek (SKA-SA) vereis word met betrekking tot die karakterisering van die komplekse omgewing van MeerKAT, is ’n deterministiese model ontwikkel wat van volgolf en asimptotiese tegnieke gebruik maak. Hierdie oplossing, wat eenvoudig na verwys word as die straalmodel, het die metode van momente (MoM) gebruik om antenna eienskappe te bepaal en vir ware grond op te los, terwyl fisiese optika gebruik is om verstrooiing van die skottels aan te spreek. Met die sagteware FEKO as die koppelvlak en simulasie enjin, is die MeerKAT kern met dié berekeningsmetode gereproduseer. Ontleding van die numeriese data het die volle omvang van elektromagnetiese kompleksiteit met betrekking tot multipadopstellings aan die lig gebring. Mees merkbaar was die ontwikkeling van hoë ruimtelike resolusie verswakkingskaarte wat beide hoë en lae risiko streke uitgewys het. Hierdie het voordele vir die identifisering van potensiële RFI probleme. Die straalmodel het egter uitgeblink wanneer dit teen metings ondersoek was (WGKF <4 dB). Dit is hoogs voordelig aangesien numeriese modellering baie meer buigsaam as fisiese toetse is. In besonder is die nuutheid en noemenswaardigheid van hierdie navorsing die vermoë om ’n werklike ontplooiing scenario met presisie en hoë akkuraatheid te reproduseer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101040
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