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This paper considers the optimization of a 150 Ω conical plate-fed reflector impulse radiating antenna (IRA) that we intend to use for shielding and propagation studies at the Square Kilometre Array (SKA) site. A time-domain measurement system is proposed due to reduced measurement times. The feed arm angle is varied to improve IRA's performance. Our simulation results show that the antenna has better...
Due to the high cost of radio frequency shielding materials, we investigate affordable alternative materials for this purpose. In the recent past, much work has been done with regard to evaluating shielding effectiveness of materials in frequency domain. However, frequency domain measurements are time-consuming when broad frequency spectra are covered. In this paper, we present shielding effectiveness...
The characterisation of the dispersion response of an extruded 3D-printed bi-conical antenna is presented using group delay and system fidelity factor (SFF). Measurements were performed in time and frequency domain using two identical antennas. A stable group delay is found and moderate correlation is observed between received and transmitted pulses.
A 3D-printing technique, combined with conductive paints, is investigated for a low-cost methodology in antenna design. The technique is applied on a conical antenna of 41° above a ground-plane using carbon and nickel-based conductive paints. An impedance bandwidth of 20:1 is achieved. Measured normalised-directivity patterns correlate with simulations and the antenna is more than 90% efficient up...
The South African Square Kilometre Array (SKA-SA) precursor instrument (MeerKAT) is being realized in the semi-desert Karoo region of the Northern Cape. Thus far, much has been achieved in terms of electromagnetic compatibility (EMC) interventions. However, recent surveys have shown that signal propagation ought to be examined in greater detail, ultimately leading to a site evaluation of the SKA-SA...
The impact of self-generated radio frequency interference (RFI) on astronomical data depend greatly on the infrastructural design of the observatory and the shielding of the equipment. Care has been 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...
The design and optimization of a conical antenna above a ground-plane for RFI monitoring are discussed with a specific focus on impedance matching to 50 ohm. Simulations using the computational electromagnetic code FEKO were used through iterative analysis to change the cone angle and cone apex height above ground-plane level. The optimized antenna design with cone to ground-plane angle of 41 degrees...
The SKA needs strong mitigation measures to ensure a radio quiet environment. In an ongoing study, lightning induced RFI is investigated as well as a means to measure and mitigate its effects. The Rogowski coil is chosen as the principle current transducer and its calibration is studied. A time domain calibration approach is investigated and verified with a commercial current probe's calibration data...
This paper describes the continued characterization of a printed-circuit-board log periodic dipole-array (PCB-LPDA) antenna used for radio frequency interference (RFI) measurements for the South African Square Kilometer Array (SA SKA) project. Earlier measurements in an anechoic chamber showed levels of uncertainty in the VHF and C bands. Measurements on an open area test site (OATS) show lower uncertainty...
Design details of a 50∶1 bandwidth printed circuit board log periodic dipole array antenna for practical radio frequency interference measurement use are discussed. A feeding tab design optimization is incorporated, which obviates the need for a dummy cable on the opposite board to balance the feed cable structure. Computer simulated and measured realized gain and reflection coefficient results are...
Our research group has contributed to the characterization and mitigation of radio frequency interference (RFI) associated with telescope and infrastructural developments for the Karoo Array Telescope. The Karoo core site is found in the Northern Cape of South Africa. The scale and computational modeling of systems and telescopes, along with actual site testing of RFI and mitigation procedures, will...
Cable transfer impedance is investigated using time domain (TD) techniques to reduce measurement duration. Two methods have been used: the current injection and the mode-tuned reverberation chamber technique. Initial transfer impedance results on RG-58 coaxial cable show good agreement between TD and frequency domain (FD) for both setups. The gated-TD approach permits larger frequency bands to be...
The Square Kilometre Array (SKA) is to be the most sensitive radio astronomy receiver ever constructed. The Karoo Array Telescope (KAT) region, part of an SKA bidding site in South Africa, has been proclaimed a radio quiet zone. This paper describes several contributions our group has made to the strategies used in the management of environmental RFI and self-generated emissions. Additionally, we...
We study the performance of a reverberation chamber for coaxial cable transfer impedance determination. The chamber is calibrated according to the relevant IEC standard 61000-4-21. The results are evaluated from radiated power measurement of a standard radiator, using an Open Area Test Site equivalent E-field approach. The transfer impedance of a 50 Ω coaxial air-line is tested with the calibrated...
The South African SKA demonstrator is founded on the Karoo Array Telescope (KAT). A holistic approach to radio frequency interference (RFI) mitigation has been adopted from the outset. We describe our group's contribution to this evolving effort. We consider the RFI beginning from the 100 km powerlines, through to the site base equipment and continue right up to the KAT-7 telescopes. A site survey...
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