The exciting Square Kilometre Array (SKA) project – a massively distributed radio telescope being built in South Africa and Australia over five years – has thrust Tellumat’s radio frequency (RF) skills into the public eye once more.

Market need
Of near-unprecedented scale in the history of scientific and engineering endeavour, SKA will consist of 2,000 mid-frequency dishes hosted in South Africa, while Australia will host the Low Frequency Array portion, consisting of 1 million antennas.

The huge collecting area will make this telescope 50 times more sensitive than the largest existing radio telescope, giving it the ability to survey the sky thousands of times faster.

The two southern hemisphere countries are supported by ten SKA member countries with consortia from 20 countries contributing to its design & construction.

The MeerKAT array, completed in 2018, is spread over 8 kilometres, 90km from Carnarvon in the Karoo. It consists of 64 off-set Gregorian dishes, and it was in this phase that Tellumat was able to prove its RF mettle. MeerKAT is a proof-of-concept precursor to SKA.

Both MeerKAT (and SKA) can observe radio sources in several frequency ranges, and Tellumat was involved in MeerKAT’s L-Band receiver, which operates in the 900 to 1670 MHz frequency range. The company designed and manufactured 140 Radio Frequency Conditioning Units (RFCUs) and spare parts for the 64 dishes making up the array.

Technology solution
Tellumat provided consulting services in 2010, during the design phase of MeerKAT – studying design options and recommending the best arrangement and specifications for the receiver – including defining the required modules and the RF interfaces between modules.

A telescopic observation can last as long as 20 minutes, meaning the receiver (including the RFCU) must perform consistently despite potential temperature changes. To minimise variations due to temperature, the RFCU module was housed in a heavy-based aluminium housing.

The RFCU pre-conditions the received signal before digitisation. Its internal functions include amplification (which can be remotely configured), filtering out unwanted signals, monitoring on-board temperature and signal levels to enable remote fault sensing, and providing high-speed signal overload protection to protect the downstream digitisation circuitry. To further enhance performance, Tellumat’s solution also minimises internally generated noise which could corrupt the weak signals being received.

As high-powered satellites and aircraft operate above the dishes, the design had to cater for very strong signals falling within the receive band of the system, without distorting the very weak signals being observed.

Benefits
Tellumat’s solution complied fully with requirements, thanks to the company’s involvement at RF system specification stage.

The company used computer modelling to run a very short development cycle, mitigating the risk of delivery delays.

The on-site environmental testing facilities at Tellumat further enabled Tellumat engineers to conduct extensive temperature testing to ensure the required performance stability at temperature extremes.

Being the first of four designs for different frequency bands (and on a new telescope) the solution had a significant risk of failure, however Tellumat engineers relied strongly on their past experience of radio telescope receiver design, which it gained during its involvement with the XDM and KAT-7 pathfinder telescopes in 2006-2009, resulting in success.