Fraunhofer IAF Low-Noise Amplifiers Aboard the Arctic Weather Satellite

Collecting accurate weather data of the Arctic for the first time and improving forecasts and climate observations worldwide — that is the task of the Arctic Weather Satellite (AWS), which ESA sent on its way to its low-Earth orbit in mid-August.

It uses a state-of-the-art microwave radiometer that contains four low-noise amplifiers from Fraunhofer IAF with world-leading InGaAs mHEMT technology.

At EuMW 2024 in Paris, the Freiburg-based institute will present exhibits of the amplifiers installed in the AWS as well as other high-frequency electronics from the application areas of satellite communications, mobile communications and low-temperature measurement technology from Sept. 24 to 26.

The Arctic Weather Satellite (AWS) of the European Space Agency (ESA) was sent on its journey to a polar orbit 600 km above the Earth on Aug. 16, 2024. On board: four low-noise amplifiers (LNAs) from the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg.

They are essential components of the passive microwave radiometer with which the AWS measures temperature and humidity in the Arctic more precisely than ever before. This should contribute to a better understanding of both the Arctic and the climate change that is particularly visible in it.

If the mission is successful, ESA plans to launch a global constellation of identical small satellites into space to enable more precise and shorter-term weather forecasts (nowcasting) and climate observations on a global scale.

The task of LNAs in technical systems is to improve the quality of incoming signals. As their name suggests, they amplify weak signals while causing as little background noise as possible so that signals can be more easily detected and analyzed. In this way, LNAs increase the sensitivity of systems.

“The more powerful a low-noise amplifier is, the more accurately and reliably a system can collect data. They play a major role in satellite-based Earth observation, as the microwave radiation that reaches the satellite radiometer is very weak,” explains Dr. Fabian Thome, deputy head of Business Unit High Frequency Electronics at Fraunhofer IAF. “It is a great confirmation and motivation that we are contributing to better research into the Arctic and its effects on the global climate with our LNAs.”

The AWS microwave radiometer consists of a rotating antenna that picks up the natural microwave radiation emitted by the Earth’s surface and transmits it to four feedhorns and four receivers.

The antenna and receiver each belong to one of four groups comprising a total of 19 channels, which together cover a frequency spectrum of 50 to 325 GHz: Eight channels with frequencies from 50 to 58 GHz measure temperature, one channel at 89 GHz detects clouds, another at 165.5 GHz both clouds and humidity, five channels between 176 and 182 GHz are only responsible for humidity, while finally four channels at 325 GHz plus/minus 1.2 to 6.6 GHz measure humidity and also detect clouds.

Fraunhofer IAF has provided a total of four LNAs for three of the four channel groups: one module for the frequency range around 54 GHz, two identical modules for 89 GHz, which were connected in series for greater overall amplification, and one module for the 170 GHz range.

The researchers have enhanced proven technologies based on the compound semiconductor indium gallium arsenide (InGaAs) and realized metamorphic high-electron-mobility transistors (mHEMTs) for monolithic microwave integrated circuits (MMICs).

“Fraunhofer IAF is a world leader in the development of transistors and circuits for satellite-based radiometry systems. Our modules define the state of the art in many performance areas,” said Thome.

In developing the modules, the researchers worked closely with the direct client ACC Omnisys (AAC Clyde Space) from Sweden, which built the radiometer system for OHB Sweden and ESA.

The AWS mission is to collect more precise weather data in the Arctic for the first time, which will enable short-term forecasts for the polar region — including so-called nowcasting, which refers to forecasts for the next few hours.

As the Arctic has a strong influence on global weather, the data also enables better global weather forecasts. This also applies to the climate: climate change is progressing faster in the Arctic than in other regions of the world. At the same time, changes in the Arctic have an impact on the global climate due to feedback effects.

If successful, an entire constellation of identical small satellites will follow the AWS: the EUMETSAT Polar System — Sterna (EPS-Sterna). The plan is to have six satellites in three different orbits at the same time to collect long-term weather data from the polar regions.

The satellite set will be renewed three times, so that a total of 18 satellites will be used during the time of the mission. Two satellites are planned as replacements. The first of six EPS-Sterna satellites is due to be launched in 2029.

With this project, ESA is pursuing the New Space approach for the first time. New Space is characterized by projects being carried out in the shortest possible time with significantly fewer resources.

In the case of AWS, whose total mass is only 150 kg, only three years passed from project start to rocket launch, during which a fraction of the cost was incurred compared to previous projects. Further advantages of New Space are the greater resilience of constellations — the failure of a satellite in the network can be compensated for or replaced quickly and cheaply — and the flexibility of missions, which can be extended or shortened if necessary, without consuming large amounts of resources.