Masters Degrees (Electrical and Electronic Engineering)

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Browsing Masters Degrees (Electrical and Electronic Engineering) by Author "Andriambeloson, Joely Andrianina"

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    Wideband coaxial cable transfer impedance for Karroo Array Telescope
    (Stellenbosch : Stellenbosch University, 2011-12) Andriambeloson, Joely Andrianina; Reader, H. C.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    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.