This industry paper describes two contemporary investigations with strong electromagnetic compatibility (EMC) requirements in South Africa:•new installation magnetic noise evaluation at the South African National Space Agency (SANSA) Space Science Centre (former Hermanus Magnetic Observatory) and,•stringent shielding effectiveness (SE) testing of the MeerKAT Telescope Array, which will form part of the international Square Kilometre Array (SKA) developments.

New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x larger than during quiescence, and has been decaying exponentially on a 111+/-19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.

ABSTRACTWe investigate the electromagnetic (EM) shielding effectiveness (SE) properties of a berm which was created from soil due to construction works near a sensitive radio astronomy site. For the analysis, the berm is approximated as being located above an infinite perfectly electric conducting (PEC) plane. A two‐dimensional cross‐sectional analysis is shown to be sufficient to investigate the SE, which we compute using a computationally efficient single‐layer boundary integral equation method. To verify the method, we compare our results against those obtained by the commercially available Method of Moments (MoM) code, FEKO. Good agreement is demonstrated. It is observed that the berm provides about 25–30 dB SE at heights lower than 5 m and at distances of up to 50 m from the berm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:17–21, 2017

The square kilometer array is planned to be the most sensitive radio telescope of the 21st Century. Electromagnetic site quietness is a critical element in achieving the full science goals. We evaluate the shielding effectiveness of a soil berm at the South African Karoo site. The berm is electrically large and computationally expensive to model. A hybrid GO/MoM model using FEKO is proposed. Simulated data are compared to full-scale multicopter measurements. Broadband antennas are built into the landing structure and their patterns are deembedded during postprocessing. Simulations and measurements over 100-900 MHz (vertically polarized) show that the berm becomes effective from the point where its height reaches ten wavelengths. Shielding effectiveness values in the range of 25 dB are predicted by an approximate perfect electrical conductor ground model; the validity of this approximation is investigated. A simple knife-edge model is shown to provide a useful estimate of likely shielding. The results show that 3-D berm optimization using computational techniques is possible.

We propose a multicopter scheme to characterize the shielding effectiveness of South Africa's Karoo Array Processing Building. The use of an autonomous multicopter with calibrated receiver and onboard antenna patterns is compared to conventional ground-based metrology. Measurement time and resolution are improved significantly. Our technique has been used during the evaluation of electromagnetic shielding policies during and after construction.

Unmanned aerial vehicles, such as Multicopters, are becoming ubiquitous. One newer field is in electromagnetic (EM) metrology [1] [2]. For such applications the vehicles are relatively complex, housing multiple subsystems with associated wiring and metallic surfaces. The galvanically interconnected subsystems have bearing on the on-board antennas and therefore the integrity of measurements.

The Karoo region in the Northern Cape of South Africa has been chosen to host the country's Square Kilometre Array (SKA) [1] telescope core due its low radio frequency interference (RFI) levels. With the construction of the Karoo Array Processor Building (KAPB), self-generated radio frequency interference (RFI) and its potential propagation into telescopes has attracted close attention throughout the design and development phases of the project. During the construction of the KAPB, excavated soil was used to form a berm. This paper presents the results of a study of the berm properties using laboratory, physical and computational scale models along with site field measurements. Real soil dielectric properties are incorporated into well-known computational electromagnetic modelling (CEM) packages. A conducting ground plane serration technique is proposed in the model to simulate infinite conditions. The models form the basis of simplified CEM versions of the real berm. The laboratory measurements closely match the CEM models to the point where the CEM models can be used for operational studies as well as planning measurements. Measurements of this berm were made using an unmanned aerial vehicle (UAV).

As part of South Africa's 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.

This paper describes the advantages and disadvantages of differential feeding of an antenna for low-frequency radio astronomy in the context of the SKA-low telescope. A series of practical measurements to test the correct functionality of the antenna + differential amplifier pair are described and results are presented and discussed.

We describe developments in a radio frequency interference (RFI) detection instrument dubbed RATTY 2. With uncertain RFI environments in mind, the system is hardware and software reconfigurable, functioning either as a spectrometer or a transient-signal analyser. RATTY 2 is equipped with a 900 MHz bandwidth, 10-bit, non-interleaved analogue-digital converter (ADC) and the data is processed on a Reconfigurable Open Architecture Computer Hardware 2 (ROACH) platform. A computer is used for post-processing dynamically-stored data. Two different strategies were followed in designing the RF front-end systems for signal conditioning prior to digitisation: 1) a single mixer, down-converting topology, and 2) a multiple Nyquist-zone sampling configuration. The two systems are evaluated and compared in this paper.

In this paper we discuss the issue of lightning in low frequency arrays for radio astronomy with the SKA telescope in mind. The non-linear nature of the lightning makes it impossible with present computational codes to derive accurate pictures of lightning current effects on large, galvanically-connected structures. We consider a linearised approach to model idealised lightning with a focus on indirect strikes. The intention is to build up an understanding of minimising lightning damage and associated RFI in the arrays. Finally, we discuss the advantages of scale prototype measurements and time gating as expedient techniques to characterize these effects in controlled environments.

The Square Kilometre Array (SKA) will be the largest radio telescope in the world. Up to 3000 dishes, and more than 500,000 array elements will be linked to obtain an extreme sensitivity. The frequency band starts at 70 MHz, and goes up to 10 GHz and possibly over 25 GHz later. Arcing on high voltage lines is a potential source of interference. Gaptype sparking is known to produce large bandwidth noise, but up to now the consequences were investigated for radio and television interference, at higher levels and over a lower frequency band than SKA. A test spark gap has been constructed. High frequency current probes determined the gap current to generate arcing. Their frequency domain transfer impedance Zt has been measured, and has been used to de-convolute the measurements.

Large scale radio astronomy (RA) activity, brought to focus in South Africa with the Square Kilometre Array (SKA) developments, only began to impact on local engineering teams from around 2004. The country's first demonstrator was ready for evaluation towards the end of 2007. It was at that point that my EMRIN group's engagement on radio frequency interference (RFI) began. After a review of a number of European RA sites, and doing some calculations of required electromagnetic quietness required for viable SKA observations, it became apparent that RFI management would be a major priority for any contemporary large radio research instruments. This talk will discuss components of site development that are now considered essential for any such instruments to be regarded as robust. The presentation will review: 1. Electromagnetic compatibility (EMC) principles illustrated with simple schematic experiments and computational electromagnetics. The pictorial material will emphasise an understanding of current paths, resistive, E and B-field coupling mechanisms and then the use of enclosures, interfaces and cabling structures [1-3]. Some suitable sensors and their calibration will be described [4-6]. 2. Various radio astronomy observatories (RAO's) that have been visited in Europe and South Africa which will be considered in the light of these principles. 3. Experience gained from the South African experimental demonstrator model (XDM), the Karoo Array Telescopes (KAT-7 and MeerKAT) and some Square Kilometre Array (SKA) precursor lower-frequency arrays [7-21]. 4. Requirements for designing robust large radio research instruments where challenges for these large science projects will be posed. The two primary purposes of the presentation will be to: a) promote the viewpoint that site and instrument construction must embrace EMC principles from the start, and b) encourage the interaction of engineers, scientists and astronomers throughout the development process.

During the last week in May this year, 35 engineers and physicists gathered at the beautiful Lohas Park in South Korea to attend the latest course on high-power electromagnetics (HPEM). This was the eighth in a series sponsored by the SUMMA Foundation, dating back to the “EMP Interaction and Hardening” course organized by Dr. Carl Baum in 1983 in Socorro, New Mexico. Dr Baum was a leader in the field of high-power electromagnetics, having pioneered much of the technical understanding in what we now refer to as EMP, HPM, and target ID. The themes of this course encompassed “Electromagnetic Environments, Effects and Protection” (EEEP). The course was directed by Dr. Dave Giri, who, according to his own My Journey with Carl memoir [1], was tasked with the responsibility to continue the tradition of offering the HPEM course series. As a broad summary of the course intention, we were referred to the notion of “Source to Target - Target to Source” [2], where one can respectively analyze the signal path leading from a source to a particular port of interest, or synthesize the problem in the reverse direction. In presenting the resources for the subject, we were led through topics of “EM Topology,” “EMP and Lightning,” “External Interaction,” “Apertures and Antennas,” “Coupling,” “HPE Environments,” “Effects,” “Shielding,” “Hardening and Protection,” “HPM Tubes and Sources,” “Pulsed Power,” and “Standards.” Faculty members, all sitting in the front row of Figure 1, shared the lecturing of these topics, which were handled in one-hour sessions.

Enclosure shielding effectiveness (SE) is investigated using a reverberation chamber methodology in the time domain (TD). The TD technique is first calibrated on an in-house coaxial airline. A nested-enclosure approach is then presented and checked against a frequency-domain (FD) equivalent evaluation. Good agreement is shown between the theoretical and measured airline results. TD and FD nested-enclosure SE agree to within 5 dB from 400 MHz to 1.2 GHz. Measurement time reduction, along with greatly increased frequency information, are derived in the TD.

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.

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 analysed.