Electromagnetic modelling of the 32-m Ghana radio telescope

This paper presents the electromagnetic modelling and supporting results of the African VLBI Network (AVN) Ghana radio telescope at the operating frequencies of 5 and 6.7 GHz. Working from limited technical data, we establish suitable geometrical parameters for the unshaped version of the Cassegrain system, including modelling and rotation of the four mirrors within the slanted beam-waveguide (BWG). The geometry implemented in GRASP (General Reflector Antenna Software Package) produces several performance values including the effects of the BWG, struts and mechanical tolerances. It is shown that the theoretical maximum gain and aperture efficiency at 5 GHz are 63.09 dBi and 72.56%, respectively. The corresponding values at 6.7 GHz are 65.80 dBi and 75.42%, respectively

Electromagnetic Gap Leakage Analysis for the SKA Mid-Frequency Dish

This paper presents electromagnetic analysis as performed on the Square Kilometre Array (SKA) mid-frequency dish in order to estimate the ground leakage caused by gaps in the main reflector. The effects of the ground leakage are shown in terms of conventional performance parameters such as gain and aperture efficiency, as well as the percentage of feed power hitting the ground behind the main reflector. Analysis were performed for SKA Band 1 and 2 with a combined frequency range of 0.4 - 1.8 GHz. It is shown that the gaps in the main reflector reduce the gain between 0.23 and 0.05 dB and could increase the noise temperature by approximately 14 K when pointed at zenith. The transmission percentage of the incident power hitting the ground is below 0.2% across the combined bands

The Hydrogen Epoch of Reionization Array Dish II: Characterization of Spectral Structure with Electromagnetic Simulations and its science Implications

We use time-domain electromagnetic simulations to determine the spectral characteristics of the Hydrogen Epoch of Reionization Arrays (HERA) antenna. These simulations are part of a multi-faceted campaign to determine the effectiveness of the dish's design for obtaining a detection of redshifted 21 cm emission from the epoch of reionization. Our simulations show the existence of reflections between HERA's suspended feed and its parabolic dish reflector that fall below -40 dB at 150 ns and, for reasonable impedance matches, have a negligible impact on HERA's ability to constrain EoR parameters. It follows that despite the reflections they introduce, dishes are effective for increasing the sensitivity of EoR experiments at relatively low cost. We find that electromagnetic resonances in the HERA feed's cylindrical skirt, which is intended to reduce cross coupling and beam ellipticity, introduces significant power at large delays ($-40$ dB at 200 ns) which can lead to some loss of measurable Fourier modes and a modest reduction in sensitivity. Even in the presence of this structure, we find that the spectral response of the antenna is sufficiently smooth for delay filtering to contain foreground emission at line-of-sight wave numbers below $k_\parallel \lesssim 0.2$ $h$Mpc$^{-1}$, in the region where the current PAPER experiment operates. Incorporating these results into a Fisher Matrix analysis, we find that the spectral structure observed in our simulations has only a small effect on the tight constraints HERA can achieve on parameters associated with the astrophysics of reionization.Comment: Accepted to ApJ, 18 pages, 17 Figures. Replacement matches accepted manuscrip

Preliminary surface charging analysis of Ariel payload dielectrics in early transfer orbit and L2-relevant space environment

Ariel [1] is the M4 mission of the ESA’s Cosmic Vision Program 2015-2025, whose aim is to characterize by lowresolution transit spectroscopy the atmospheres of over one thousand warm and hot exoplanets orbiting nearby stars. The operational orbit of the spacecraft is baselined as a large amplitude halo orbit around the Sun-Earth L2 Lagrangian point, as it offers the possibility of long uninterrupted observations in a fairly stable radiative and thermo-mechanical environment. A direct escape injection with a single passage through the Earth radiation belts and no eclipses is foreseen. The space environment around Earth and L2 presents significant design challenges to all spacecraft, including the effects of interactions with Sun radiation and charged particles owning to the surrounding plasma environment, potentially leading to dielectrics charging and unwanted electrostatic discharge (ESD) phenomena endangering the Payload operations and its data integrity. Here, we present some preliminary simulations and analyses about the Ariel Payload dielectrics and semiconductors charging along the transfer orbit from launch to L2 include

Investigation and characterization of the HERA dish and feed using electromagnetic simulations

Thesis (MEng)--Stellenbosch University, 2016.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.AFRIKAANSE OPSOMMING: Hierdie tesis lewer resultate van die elektromagnetiese ontleding van die Hydrogen Epoch of Reionization Array (HERA) eksperiment se skottel en voer. Die uitdagende wetenskapsdoel vir HERA is die opsporing en karakterisering van die Epog van Herionisasie (EoR) se drywing. Deur ’n ondersoek te doen van die HERA skottel, word dit bepaal dat die panele waaruit die skottel saamgestel is, nie ’n groot afwyking van ’n perfekte parabool veroorsaak nie. Die skerm bo-op die skottel veroorsaak wel variasies in die aanwins teenoor frekwensie. Die wedersydse-koppeling tussen ’n aantal HERA elemente het nie ’n groot invloed nie, selfs sonder die skerm. By 150 MHz word daar gevind dat die HERA skottel ’n sigveld van ongeveer 9˚ het en sy-lob vlakke van 15 dB minder as die hoofbundel, wat ’n aanwins van 25 dB het. Die drywingspatroon by die horison word gemeet by ongeveer 40 dB minder as die hoofbundel. Die uv-dekking van HERA word bereken vir ’n nou-verpakte seshoek konfigurasie. Met die insluiting van wydomliggende elemente, verbeter die uv-dekking aansienlik en word daar aangedui dat HERA uitstekende beeld-vermoëns sal hê. Die vertraging-spektrum tegniek wat gebruik word deur HERA sterrekundiges word ondersoek en toegepas op die HERA skottel met behulp van elektromagnetiese simulasies en post-verwerking. Dit word vasgestel dat weerkaatsings van die skottel nie voldoen aan die -60 dB seinsterkte na 60 ns spesifikasie nie. Inteendeel, die weerkaatsings word gemeet by -35 dB. Resultate van modellering en optimering in die frekwensiegebied van alternatiewe voere vir HERA word vergelyk met die huidige PAPER voer. Dit sluit verskeie weergawes van die strikdasvoer, ’n geskaalde PAPER voer en ’n kronkelende voer in, wat ook gebou en getoets is. Daar word aangetoon dat so ’n poging, in samewerking met ’n reflektor, uitdagend is as gevolg van die lae-frekwensie band