Characterization of RF signal coupling into MeerKAT telescopes

Kuja, Stanley Okoth (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The study of weaker astronomical waves originating from billions of light years away could give an insight into the dawn of the universe's history. This requires the use of highly sensitive radio receivers and large radio telescopes for the detection of such mysterious signals. The MeerKAT facility will form part of the square kilometre array (SKA) which will have orders of magnitude greater sensitivity than existing radio telescopes. However, radio frequency interference (RFI) becomes a concomitant worry to such sensitive equipment. The proximity of adjacent structures of the MeerKAT dishes at the core area, provides a possibility of a high inter-coupling problem between the nearby dishes, even from low-level emissions due to currents on structure cables. This thesis focuses on the electromagnetic (EM) characterization of a single dish using a physical scale model and computational electromagnetic (CEM) modelling. Together with eld measurements, the veri ed CEM model can be used for further investigations into coupling between MeerKAT antennas. The South African SKA has ensured that care is taken in the shielding design of critical areas on the MeerKAT structure including the receiver indexer (RI) and cable entry point (stub-up). Due to the extreme sensitivity of the project, we qualify the shielding e ectiveness with computational and scale modelling and on{site radio frequency (RF) coupling investigations on the MeerKAT dish structures. The CEM code FEKO and method of moments frequency domain numerical technique is utilised throughout the study. The FEKO model veri cation is successfully achieved through measurement of a physical scale model in an anechoic chamber. The validated CEM model is con dently used to complement eld measurements. A good correlation is attained between measurement and simulation through the transfer function determined from an incident electric eld and the associated coupled currents on di erent cables that route to the RI and the earth cable at the stub{up region. The veri ed CEM model can now be used for dish to dish coupling studies which will predict the nature of EM environment at the core site and lead to possible recommendations before the full commissioning of the entire array of MeerKAT antennas.

AFRIKAANSE OPSOMMING: Die studie van swakker astronomiese golwe afkomstig van biljoene ligjare weg kan insig gee aan die begin van die heelal se geskiedenis. Om hierdie geheimsinnige seine op te tel benodig die gebruik van hoogs sensitiewe radio ontvangers en groot radio teleskope. Die MeerKAT fasiliteit sal deel vorm van die Square Kilometer Array (SKA) wat ordes meer sensitiwiteit as enige bestaande radio teleskoop sal h^e. Radiofrekwensie-steuring is egter 'n gepaardgaande bekommernis met sensitiewe toerusting van hierdie aard. Die nabyheid van die aangrensende strukture in die kern-area van die MeerKAT skottels bied 'n moontlikheid van hoë interkoppeling probleme aan tussen die nabygeleë skottels, wat selfs veroorsaak word deur lae{vlak emissie as gevolg van strome op die kabels van die struktuur. Hierdie tesis fokus op die elektromagnetiese (EM) karakterisering van 'n enkele skottel met behulp van 'n fisiese skaalmodel en elektromagnetiese modellering deur rekenaar sagteware. Saam met die veld{metings kan die geverifieerde sagteware-model gebruik word om verdere ondersoek in te stel oor die koppeling tussen die MeerKAT antennas. Die Suid-Afrikaanse SKA het verseker dat sorg getref word in die afskerming ontwerp van kritieke areas van die MeerKAT struktuur, insluitend die ontvanger aanwyser en kabel intree punt. As gevolg van die uiterste sensitiwiteit van die projek, staaf ons die doeltreffendheid van die afskerming met sagteware en skaal{modellering, asook deur die ondersoek van die radiofrekwensie (RF) koppeling van die MeerKAT skottel strukture op die terrein self. Die EM sagteware-kode FEKO en die frekwensie{domein numeriese tegniek genaamd metode van momente is aangewend regdeur hierdie studie. Verifikasie van die FEKO-model is suksesvol bereik deur die meting van 'n fisiese model in 'n anegoïese kamer. Die goedgekeurde EM sagteware{model is met selfvertroue gebruik om die veld-metings aan te vul. 'n Goeie korrelasie word bereik tussen meting en simulasie deur die oordragsfunksie, wat bepaal word vanaf 'n inkomende elektriese veld en die gepaardgaande gekoppelde strome op verskillende kabels. Hierdie kabels span na die ontvanger aanwyser en die gronddraad by die kabel intree gebied. Die geverifieerde EM sagteware-model kan vorentoe gebruik word vir skottel-tot-skottel koppeling studies wat die aard van die EM-omgewing by die kern-terrain kan voorspel en lei tot moontlike aanbevelings voor die ingebruikneming van die hele opstelling van MeerKAT antennas.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97979
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