Manufacture of MeerKat antennas will boost local industry

April 23rd, 2014, Published in Articles: EngineerIT


Hans van de Groenendaal, features editor, EngineerIT

At least 75% of the components making up the 64 MeerKAT antennas will be manufactured in South Africa, but several industries in the SKA Organisation partner countries are also making crucial contributions. The global technology collaborations bring cutting-edge know-how and many years of antenna experience to the MeerKAT project, and are designed to transfer expertise to the South African industry partners.

“The launch of the first MeerKAT antenna signifies South Africa’s ardent commitment to the MeerKAT project and the broader Square Kilometre  Array (SKA) project. It typifies the excellent engineering and technical capabilities in South Africa that have enabled us to deliver a project of this magnitude within projected timeframes and budget allocations,” said Science and Technology Minister Derek  Hanekom at the launch of the first MeerKat dish. “Equally significant is the launch of the processor building and the associated design and development activities which mark South Africa’s readiness to embark on a big data programme at national level.”

Artist impression of the first MeerKat dish

Artist’s impression of the first MeerKat dish.

Standing 19, 5 m tall and weighing 42 tons, the new MeerKAT antenna towers above the antennas of the nearby KAT-7 instrument. KAT-7 was completed in 2010 as an engineering prototype for MeerKAT, and is now routinely used for scientific research. MeerKAT is one of the precursors to the SKA telescope, and will later be incorporated into the mid-frequency component of SKA Phase 1 when that instrument is constructed.

Because of its “Offset Gregorian” design, each MeerKAT antenna has two reflectors: a main reflector with a 13,5 m projected diameter and a smaller sub-reflector with a diameter of 3,8 m. “With this design there are no struts in the way to block or scatter incoming electromagnetic signals,” said Prof. Justin Jonas, speaking on the South African Radio League’s nation-wide interactivity technical discussion network.  “This means that the instrument will be more sensitive than a more conventional symmetric design, and will deliver excellent imaging quality.”

“It is significant that signals received on any of the four receiving heads mounted on a rotating platform will be digitised at the  receiver heads and transported as digital signals to the partial underground processing centre on the Karoo SKA site via optic fibre cable. Following this process, means that the coaxial feed is limited to under a metre long, reducing significant signal losses that would have occurred if a strait coaxial feed was used all the way to the processing centre. To cover the frequency range four receivers are mounted on a rotating table and are moved into position as required.”

The full MeerKAT array will consist of 64 identical receptors (antennas with receivers, digitisers and other electronics installed). Connected by 170 km of underground fibre optic cable, the 64 receptors will operate as a single, highly sensitive astronomical instrument, controlled and monitored remotely from the MeerKAT control room in Cape Town.

Data will flow via buried optical fibres from each receptor to the Karoo Array Processor Building (KAPB), which will house all the racks of digital data processing systems and the electrical power equipment. “The processed data is then sent to the MeerKAT archive in Cape Town, and onto science collaborators in South Africa and abroad.

“Once up and running, the MeerKAT will generate enough data from the antennas to fill about four and a half million standard 4,7 GB DVDs in a day,” Dr. Jasper Horrell, general manager for science computing and innovation at SKA SA explains. “However, much of this data is processed on-the-fly and the archive will initially be sized at the equivalent of about 2-million DVDs, retaining some of the larger volume, less processed data for shorter periods and only retaining the smaller volume, more processed science data products indefinitely.”

Entrance to the processing building which has been constructed partial underground

Entrance to the processing building which has been constructed partially underground.

The KAPB is 5 m below ground level in order to protect MeerKAT from radio frequency interference (RFI) generated by the electrical and electronic equipment housed in the data centre. Being underground also enhances the thermal efficiency of the building. The racks of data processing systems are housed in a huge shielded enclosure within the underground KAPB. This “steel box” is constructed from special steel panels that make sure that no RFI generated by the fast digital electronics “leaks out”. An extremely precise atomic clock, a hydrogen maser, will be located in a separately partitioned room to ensure thermal stability of this precision device.

Netherlands-based Comtest Engineering  provided the shielding (steel panels and RFI-tight doors), while the installation was done by a local company, ITC Services. This is a good example of maximising local content, while also drawing on international expertise.

Comtest Engineering has done many RF shielding projects over the past 30 years, but taking four sea containers with roughly 48 tons of shielding materials deep into the Karoo and have it built like this, was a challenge but with the support of the ITC installation team in South Africa Comtest said it was managed successfully.

The entire on-site infrastructure (buildings, roads, electrical power conditioning and reticulation, aircraft landing strip, etc. has been constructed by South African companies, and the SKA SA infrastructure team based in Johannesburg managed the complex project.

SKA SA engineers and contracted manufacturing companies will now continue to produce the massive, high-precision components of the remaining MeerKAT antennas, and install the antennas in the Karoo, according to a tight timeline. By the end of 2014, the first four receptors will be standing in the Karoo. All 64 receptors will be installed by the end of 2016, with final commissioning being completed in 2017.

At least 75% of the components making up the MeerKAT antennas will be manufactured in South Africa, but several industries in SKA Organisation partner countries around the world are also making crucial contributions. The global technology collaborations bring cutting-edge know-how and many years of antenna experience to the MeerKAT project, and are designed to transfer expertise to the South African industry partners. For example, the first set of reflector panels, as well as the first receiver indexer and sub-reflector were manufactured abroad, but the remainder of these will be made locally.

Key local suppliers of major antenna components include Efficient Engineering (pedestal and yoke), Titanus Slew Rings (azimuth bearing) and Tricom Structures (back-up structure).

Vertex Antennentechnik  in Germany is playing a key role on the contract to provide the MeerKAT antenna positioners. The company has been responsible for a significant portion of the antenna design and analysis work, and will be providing the control system for the antennas as a sub-contractor to GDSatcom/Stratosat.

The extremely sensitive cryogenically cooled MeerKAT radio receivers were developed by South African company EMSS Antennas (Stellenbosch), and the UK company Oxford Cryosystems will provide the cryogenic cold-heads that are critical components of these receivers. These two companies have collaborated closely to develop a cold-head that is optimised for the MeerKAT application.

The National Research Council of Canada (NRC), through the Herzberg Programmes in Astronomy and Astrophysics developed the low-noise amplifiers (LNAs) that were chosen for MeerKAT’s L-Band receivers (0,9-1,67 GHz). “The LNAs are critically important in achieving MeerKAT’s sensitivity and the LNAs from NRC Herzberg were at least 5% more sensitive than any others that  could  hve been sourced from leading suppliers around the world. The LNAs for the L-Band receivers are about to enter production through a sub-contract to industry, while NRC Herzberg completes development of the LNAs for the ultra high frequency (UHF) band (0,58 – 1,015 GHz). In challenging the orthodoxy of using metal panels for large dishes, the NRC has developed world-leading expertise in the application of composite structures to radio telescopes and will provide the complex 3,8-m sub-reflector for the first of the MeerKAT antennas.

Astronomy teams from around the world have signed up to start using MeerKAT as soon as 16 of its receptors have been commissioned (around June 2015). The full array should be doing routine science observations by the end of 2017.

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