Doctoral Degrees (Electrical and Electronic Engineering)

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

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    Reverberation chamber time and frequency metrology for MeerKAT systems shielding evaluation
    (Stellenbosch : Stellenbosch University, 2014-12) Andriambeloson, Joely Andrianina; Reader, Howard Charles; Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Electromagnetic shielding plays a significant role in the protection of electronic equipment. Its application is essential for mitigating radio-frequency interference for the Karoo Array Telescope (MeerKAT) project in the Karoo region of the Northern Cape. In this context, time-domain (TD) methodology for small enclosure shielding effectiveness (SE) is developed using a reverberated environment technique. Interest revolves around measurement time speed-up and an extended SE response which covers the under-moded condition of small enclosures. Recommended IEC standard 61000-4-21 [1] e ciency of 0.75, for log-periodic dipole array (LPDA) antenna, is also validated from a reverberation chamber (RC) characterisation of a printed circuit-board (PCB) LPDA e ciency. A built-in pulse generator and the Square Kilometre Array (SKA) receiver RATTY form the main elements of the TD metrology. For validation purpose, a reference coaxial airline is built. The cable is characterised with computational codes (CST and FEKO) and is also modelled with Vance and Kley's analytical expressions. The results are compared with TD transfer impedance (Zt) measurement within the RC. The study shows that the cable fixture within an RC shapes the cable under-test (CUT) Zt. The airline itself is also introducing an oscillating component within Zt. The resonance is proportional to the CUT length and it is visible within the measurement data and the simulations. It is not, however, taken into account by the theoretical models. The consequence of an incorrect antenna efficiency on RC applications is also addressed using a PCB LPDA antenna efficiency investigation. The unknown LPDA is simulated with CST for the study. The result is compared to an RC measurement validating the IEC 61000-4-21 standard efficiency recommendation of 0.75 [1]. This methodology characterised the unknown antenna parameter from a reference dipole antenna efficiency we investigated with FEKO. Simulated Wheeler-cap techniques permitted the reference antenna validation. We found that an inaccurate LPDA efficiency has little effect at higher frequency if the IEC efficiency is adopted. However, a difference of more than 7 dB can arise at low frequency if the real efficiency differs by more than 0.3 with respect to the IEC value. The study highlights the importance of a correct antenna efficiency for accurate RC applications. The nested-enclosure technique is regarded as the conventional method of investigating small enclosures SE [2]. The technique is in general time-consuming and works for a frequency range higher than three times the enclosure under test (EUT) lowest cut-o value. Our TD metrology covers a frequency band up to 1.4 GHz which coincides with our enclosure under-moded region. The SE characterisation is not well-documented within this particular region. The dissertation contributes to this field using a non-stirred nested-enclosure configuration. In contrast to the conventional use of the nested-enclosure methodology [2], the source is placed here within the EUT and the enclosure is treated as a normal radiator. The SE definition according to the IEEE standard in [2] is followed and the enclosure total transferred-power is computed from the port's reflection coeficient. The approach does not require a stirrer for the EUT. Our measurement shows an SE agreement between the modfied and the appropriate nested-enclosure technique from 390 MHz up to 4 GHz. The investigation is faster, but in addition the TD spectrum gives a more detailed SE response than the FD approach.