Telescope technology developed by CSIRO will soon head to the world’s second largest fully-steerable radio telescope dish in the world. The Max Planck Institute for Radioastronomy’s (MPIfR) Effelsberg radio telescope is located near Bonn, Germany.
At 100 m in diameter, it is the largest dish of its kind in Europe. The technology – a phased array feed, or PAF – to be used at Bonn was originally developed for the Australian Square Kilometre Array Pathfinder (ASKAP). Once the PAF is installed at the dish, astronomers will be able to survey large areas of the sky faster and more often for new discoveries.
This is due to the PAF’s field of view, which is 30 times greater than traditional ‘single-pixel’ receivers. “It’s an exciting new technology for astronomy that basically lets us capture more information from each radio telescope at the same time,” said Aaron Chippendale, senior research engineer at CSIRO.
This is a significant advantage for astronomers, who can often spend a lot of time pointing an antenna to a particular part of the sky before they are able to move onto the next section. Astronomers can also take high fidelity images of the areas that are being mapped and even cancel unwanted radio signals from the built environment that would otherwise hinder or prevent scientific measurements.
One of the challenges of developing more sophisticated astronomy equipment includes managing the amount of instrument noise and unwanted signals that are collected. “Astronomy signals are very weak. If you put a mobile phone on the moon, it would be, by far, one of the strongest sources in the sky compared to the natural radio sources that astronomers observe,” Chippendale said. “We need to be very careful that our receivers add as little noise as possible to each measurement.”
The receivers can be so sensitive that even just thermal radio emission from the surrounding terrain leaking into them can have a significant impact. This meant CSIRO needed to make detailed electromagnetic models of not just the 188 antenna elements of the PAF, but also the low-noise amplifiers and receiver electronics that are connected to each element.
“You have to understand the complicated coupling between all 188 sensors and then optimise the design to achieve good noise performance as a complete system, including the receiver electronics and the telescope dish itself,” Chippendale said. This involved designing for electronics modules that could be easily replaced and using new materials and technologies.
For example, instead of having large bundles of coaxial cables made of copper, small, thin, lightweight bundles of fibers that are easy to connect were used to take the signal several kilometers without losing signal quality. The team also used composite materials to make a tailored, low-profile casing for the PAF with service hatches and in-built electromagnetic shielding.
Another composite material was used to add stiffness to the active face of the PAF and allow a lighter overall receiver weight. “There’s also a number of broader technical innovations just to make the system practical to maintain without needing people to directly service it very often,” Chippendale said.
CSIRO also needed to develop software to control the complex systems remotely and provide information to astronomers in a user friendly fashion. MPIfR and CSIRO will initially use the PAF to look for fast radio bursts (FRBs), an unexplained radio emission that lasts only a millisecond but appears to come from the distant universe. Currently, witnessing these bursts is a matter of chance and looking at the right spot at the right time.
But the PAF will open up the amount of sky astronomers can look at in one go and increase their chances of discovery. “Astronomers are struggling to figure out what generates these bursts and how they’re distributed throughout the universe,” Chippendale said. The PAF is currently being prepared for scientific observations on the 64 m radio telescope at Parkes in New South Wales, in preparation for the deployment in Germany.
“We’ve managed to do multiple-beam measurements of known pulsars and determine the system’s sensitivity on multiple beams across the field of view, and the results are encouraging. It has a receiver sensitivity that’s comparable to or exceeding that which we achieve with the same array feeds on CSIRO’s ASKAP telescope in Western Australia,” Chippendale said.
While work towards a first search for FRBs with the PAF at Parkes is going well, the environment near Bonn will pose different challenges for the team, such as its location in a more densely populated environment with more radio frequency interference from human technology.
Astronomers will also need to come up to speed on how to use the PAF – it is one of the first few deployments around the world that’s being used for regular astronomy, rather than engineering development. “That means we have to help build a community of astronomers who know how to get the best out of these new systems,” Chippendale said.
“That requires engineers to learn a bit of astronomy and astronomers to learn a bit of engineering and work together.” The PAF will stay at Parkes until September or October this year. By the end of this year or early next year, it will be operational at Effelsberg.
[Image: John Sarkissian (CSIRO)]