Low-noise amplifiers unlock new capabilities for the ALMA radio telescope

Engineers from the Max Planck Institute for Radio Astronomy (MPIfR) and the Fraunhofer Institute for Applied Solid State Physics (IAF) are expanding the observation capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA), a network of radio telescopes in Chile's Atacama Desert. Newly developed low-noise amplifiers enable the construction of receivers that can detect radio waves with unprecedented sensitivity.

Observing radio waves from the depths of the universe is as exciting as it is challenging. Many objects and phenomena – such as dusty disks in young star systems, complex molecules, or magnetic fields in our galaxy – only reveal their secrets at frequencies that are invisible to the human eye. However, their radio emission is so weak that it can only be detected with great technical effort and must first be amplified in several stages before scientific analysis.

With 66 telescopes, ALMA is one of the most powerful research facilities in the world. Engineers at the MPIfR in Bonn and the Fraunhofer IAF in Freiburg have now made decisive improvements to a new set of receivers that detect radio waves with frequencies between 67 and 116 gigahertz (GHz) using 145 extremely low-noise amplifiers (LNAs). The LNAs form the first and therefore crucial amplifier stage: “The performance of receivers depends largely on the performance of the first high-frequency amplifiers installed in them,” explains Fabian Thome, head of the subproject at Fraunhofer IAF. “Our technology is characterized by an average noise temperature of 22 Kelvin, which is unmatched worldwide.” With the new LNAs, signals can be amplified more than 300-fold in the first step.

At the heart of the LNAs are integrated microwave circuits developed by Fraunhofer IAF. Engineers at MPIfR designed the complex housings, which were manufactured in the institute's own precision engineering workshop, and carried out the high-precision integration of the microwave circuits and signal lines with an accuracy of a few micrometers. They then tested each amplifier at temperatures of 15 Kelvin (approximately -258 degrees Celsius) – the temperature to which the ALMA receivers must be cooled. The LNAs play a crucial role in a new and major phase for ALMA: they pave the way for the next generation of receivers that will be available in the 2030s with greater bandwidths and increased sensitivity. “This is a wonderful recognition of our fantastic collaboration with Fraunhofer IAF, which shows that our amplifiers are not only ‘made in Germany’ but also the best in the world,” says Michael Kramer, executive director at MPIfR.

The European Southern Observatory (ESO), which operates ALMA in cooperation with other international institutions, commissioned the MPIfR and Fraunhofer IAF to jointly supply the LNAs. Both research institutes benefited from around 20 years of collaboration, during which targeted funding and efforts enabled them to build up expertise that makes the institutes largely independent of non-European suppliers. The LNAs are unrivalled worldwide in their frequency range and are freely available on the European market.