ALMA completes band two receiver chain with low noise amplifiers

by Robert Schreiber
Berlin, Germany (SPX) Dec 17, 2025

The Atacama Large Millimeter/Submillimeter Array (ALMA) in the Chilean Andes is one of the most powerful radio telescope facilities used to probe cold and distant regions of the universe. Researchers use it to study how stars, planets, galaxies and potential precursors of life form by measuring millimeter and submillimeter radiation from cold molecular clouds. These molecular clouds are interstellar gas clouds with temperatures of only a few tens of Kelvin, where stars form once density and temperature conditions are suitable.

ALMA operates 66 individual parabolic antennas with diameters of 12 meters or 7 meters, each equipped with high-frequency receivers that together span ten wavelength ranges between 6 and 8.6 millimeters, corresponding to 35 - 50 GHz, and between 0.3 and 0.4 millimeters, corresponding to 787 - 950 GHz. For Band 2, covering wavelengths from 2.6 to 4.5 millimeters, or 67 - 116 GHz, the Fraunhofer Institute for Applied Solid State Physics IAF and the Max Planck Institute for Radio Astronomy (MPIfR) have now supplied 145 low-noise amplifiers. With these modules installed, all ALMA bands are equipped for the first time.

With ALMA's Band 2 capability, astronomers expect to examine the cold interstellar medium in more detail, including the mixture of dust, gas, radiation and magnetic fields that gives rise to star formation. The upgraded receivers will also support closer studies of complex organic molecules in nearby galaxies, regarded as precursors to biological building blocks, and allow more detailed observations of planet-forming disks.

"The performance of receivers depends largely on the performance of the first high-frequency amplifiers installed in them," explains Dr. Fabian Thome, head of the subproject at Fraunhofer IAF. "Our technology is characterized by an average noise temperature of 22 K, which is unmatched worldwide." With the new low-noise amplifiers, signals can be amplified more than 300-fold in the first stage, improving sensitivity to faint millimeter and submillimeter emission. "This enables the ALMA receivers to measure millimeter and submillimeter radiation from the depths of the universe much more precisely and obtain better data. We are incredibly proud that our LNA technology is helping us to better understand the origins of stars and entire galaxies."

"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 Prof. Dr. Michael Kramer, executive director at MPIfR.

At the core of the Band 2 amplifiers are monolithic microwave integrated circuits based on metamorphic high-electron-mobility transistors that Fraunhofer IAF developed using indium gallium arsenide compound semiconductor material. This technology produces low-noise amplifiers with low noise temperatures, which strengthen the astronomical signal while adding little background noise and therefore increase receiver sensitivity. As their name suggests, low-noise amplifiers enhance incoming signals by increasing their amplitude while minimizing added interference.

The European Southern Observatory commissioned Fraunhofer IAF and MPIfR to develop and deliver the Band 2 low-noise amplifier modules for ALMA, which ESO operates together with international partners. Fraunhofer IAF designed and manufactured the MMICs, conducted room-temperature tests and selected suitable chips, while MPIfR managed module assembly and qualification. Qualification included cryogenic measurements at 15 K to confirm that the modules meet ESO requirements for use in the ALMA Band 2 receivers.

ALMA was built on the Chajnantor Plateau in the Atacama Desert at an altitude of about 5000 meters above sea level to improve the accuracy of radio astronomical measurements. At this high and dry site, millimeter and submillimeter radiation from distant cosmic regions passes through less atmospheric water vapor and is therefore less attenuated than at lower, more humid locations.

The observatory is jointly operated by ESO, the US National Science Foundation and the Japanese National Institutes of Natural Sciences in cooperation with the Republic of Chile. ESO supports ALMA on behalf of its member countries, including Belgium, Denmark, Germany, Finland, France, Great Britain, Ireland, Italy, the Netherlands, Austria, Poland, Portugal, Spain, Sweden, Switzerland, the Czech Republic and Chile. The US National Science Foundation contributes in collaboration with the National Research Council of Canada and the Taiwanese National Science Council, while the Japanese National Institutes of Natural Sciences work with Academia Sinica in Taiwan and the Korea Astronomy and Space Science Institute.