MEERKAT 63 RECEIVERS
A host of receivers on the antenna provides high fidelity and sensitivity and was informed by the KAT-7 prototype
Photo by: Schalk Burger
Multiple and more sensitive receivers are being deployed on the 64 antennas of the MeerKAT radio telescope array, which will improve the scientific data it gathers, says Square Kilometre Array (SKA) South Africa science and engineering associate director professor Justin Jonas.
“The good design of the telescope prompted the Max Planck Institute for Radio Astronomy, in Bonn, Germany, to invest €11-million to build new sets of radio receivers operating in the S-band of radio frequencies, which will be deployed on the MeerKAT antennas,” says SKA South Africa project director Dr Bernie Fanaroff.
“Further, the range of receivers that will be installed on the antennas are more effective than was originally anticipated during the initial design stages and are four times faster than we thought they would be, making the telescope twice as effective,” he notes.
Each receiver is cooled to a very low temperature to reduce thermal noise, or interference, produced by the molecules in the receivers. This improves the sensitivity of the receivers.
“The project is part of a large international consortium, which assisted directly and indirectly with the designs, specifications and engineering support for our excellent South African team. The sensitivity of the dishes and the fidelity of the results are a consequence of complex design and good engineering,” says Jonas.
The operational seven-antenna Karoo Array Telescope-7 (KAT-7) is an engineering prototype that informed the MeerKAT antenna design, including mechanical, thermal, electrical and electronic design criteria.
For example, the dishes of the antennas may not move more than 1 mm, even in high winds, says MeerKAT project manager Willem Esterhuizen.
The dual-gear and ratchet system to turn the MeerKAT dishes and a host of other designs are the results of lessons learned from building and operating KAT-7.
“KAT-7 has a 100 KV uninterrupted power supply (UPS) and a 100 KV diesel generator. “The UPS insulates the antennas from electricity spikes and harmonics caused by load-shedding and general grid fluctuations, and provides three to four minutes of power before the generator starts up.
“We have learned lessons from KAT-7 and each MeerKAT antenna has a rotary UPS system, similarly, to insulate it from the grid and provide backup power until the generator starts to provide power. “The rotary UPS has been proven to induce negligible vibrations on the antenna,” says Esterhuizen.
Further, the design of the MeerKAT dishes is significantly different from the single-piece dishes of KAT-7. The UPS and generator required to power each MeerKAT antenna during grid outages are integrated into the base of each antenna.
Each 13.5-m-diameter MeerKAT dish, the reflective surface that directs signals to the receivers, comprises 40 aluminium pieces fitted together.
Satellite and wireless communications manufacturer Stratosat Datacom, in partnership with aerospace and defence company General Dynamics SatCom, established a reflective-panel manufacturing facility in Kempton Park, Gauteng, to produce these and other components. About 75% of the value of the MeerKAT array is produced in South Africa.
The analogue signals produced by the receivers on each antenna are converted into digital signals by systems in the base of the antenna. Some noise is eliminated during digitisation and the data is then sent through a fibre-optic network to the Karoo Processing Facility, says Jonas.
“MeerKAT has good angular resolution, and we can also direct and focus the beams (the columns within which the antennas detect signals) accurately. “This means that we can eliminate significant amounts of noise, such as those from other cosmic sources or interference from satellites.”
Further, the MeerKAT antenna operators, based in the control centre, in Cape Town, can also focus the inputs from the antennas using electronic systems.
The MeerKAT operates under the Open Skies principle, and researchers, academics and astronomers worldwide will have access to the data. About five years worth of research time on the MeerKAT has been dedicated to international teams, while local academia and researchers have also been allocated considerable research time.
This reflects the growing understanding that small teams cannot handle the data alone, that large science projects require large teams and that, to produce the best science, sharing and collaboration are necessary, he says.
“However, we can take credit for the fact that the world wants to use this antenna, which is providing international and local benefits,” enthuses Jonas.