Browsing by Author "Venter, Mariet"

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    Investigation and characterization of the HERA dish and feed using electromagnetic simulations
    (Stellenbosch : Stellenbosch University, 2016-03) Venter, Mariet; Davidson, D. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: This thesis presents the results of the electromagnetic analysis of the dish and feed for the Hydrogen Epoch of Reionization Array (HERA) experiment. The science goal for HERA is a challenging task in the form of detecting and characterizing the power spectrum of the Epoch of Reionization (EoR). The HERA faceted parabolic dish is investigated where it is determined that, at the relevant frequencies, the panels forming the dish is not a significant deviation from a perfect paraboloid. However, the screen placed on the dish does cause variations in the gain across frequency. The mutual coupling between several HERA elements is determined not to be significant even without including the screen. Furthermore, at 150 MHz it is found that the HERA dish delivers a Field of View of approximately 9˚ and sidelobe levels of 15 dB below the main beam, which has a gain of 25 dB. The beam level at the horizon is measured at approximately 40 dB below the main beam. The uv-coverage of HERA as an interferometer is calculated for a tight-packed hexagon configuration. With the inclusion of outlier elements, this coverage improves significantly and it is shown that HERA will have excellent imaging capabilities. The delay-spectrum technique used by HERA astronomers is unpacked and applied to the HERA dish using electromagnetic simulations and post-processing. It is determined that reflections off the dish does not meet the -60 dB power after 60 ns specification. Rather, these reflections are measured at -35 dB. Results from modelling and optimization in the frequency domain of alternative feeds for HERA is compared to the current PAPER feed. This includes several versions of the bowtie feed, a scaled PAPER feed and a sinuous feed, which is also manufactured and measured. It is shown that such an effort in conjunction with a reflector is met with challenges due to the low frequency band.