P. G. Wiid

MeerKAT RFI environment modeling and metrology

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 be outlined in this overview paper. A challenge for RFI management for South African and Australian future Square Kilometre Array developments will be posed.

South African SKA demonstrator systems: Evolving RFI mitigation investigations

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 groups 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 was conducted with systems initially deactivated and then individually switched on to determine signature characteristics. More detailed studies include analysis of telescope pedestal shielding interfaces and cable transfer impedance.

Karoo Array Telescope: Lightning protection issues and RFI

A computational electromagnetic (CEM) code and a reduced scale model were used to characterize the design of the Karoo Array Telescope (MeerKAT), South Africas demonstrator for the Square Kilometer Array (SKA). Different excitation techniques were used in the CEM code and are compared to actual scale model measurements in an anechoic chamber. With verified computational modeling, the optimized lightning down conductor layout and earth termination system interconnections were investigated, keeping cost and RFI in mind.

The answer is in fact 41, or How to get 35:1 bandwidth from a cone antenna

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 and cone apex at ground-plane level was manufactured and achieved a measured -10 dB impedance bandwidth of 35:1.

A 3D-printed PLA plastic conical antenna with conductive-paint coating for RFI measurements on MeerKAT site

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 to 5 GHz.

Towards electromagnetic characterization of MeerKAT Telescope

As part of South Africas Square Kilometre Array (SKA) programme, the Karoo Array Telescopes (KAT) KAT-7 and MeerKAT have been developed. Lightning protection and radio frequency interference (RFI) mitigation form essential parts in the design of the KAT systems. Electromagnetic (EM) characterization of single dish structures has been done using computational electromagnetic (CEM) and reduced scale modeling. This paper describes progress on EM and RFI characterization of the MeerKAT design, with specific focus on lightning-induced RFI, lightning surge protection, and earthing.

A practical 50∶1 bandwidth PCB-LPDA antenna for MeerKAT RFI studies

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 shown from 50 MHz to 8 GHz. Although the antenna works well over its intended bandwidth of 150 MHz to 7.5 GHz, it can be used down to 70 MHz.

Characterization of RF signal coupling between MeerKAT telescope structures

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 shielding effectiveness with scale modelling and on-site radio frequency (RF) coupling investigations on the MeerKAT dish structures. A simplified physical scale model and a computational model are used for electromagnetic (EM) characterization on a single dish. Together with field measurements, the verified computational model can be used for further investigations into coupling between MeerKAT telescope structures.

Lower uncertainty PCB-LPDA antenna measurement on open area test site

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 results for these frequency ranges. Simulations using the computational electromagnetic code FEKO give more insight into the differences between measurement results below 150 MHz.

Propagation modelling for the South African SKA site

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 facility. Propagation modelling is the first step in this process. Hence, the Egli model, ITU-R P.1546 and the Longley-Rice Irregular Terrain Model (ITM) are evaluated as propagation tools for use in the Karoo. The results show that optimizations are required to better predict path loss in the Karoo environment.