Clear message from orbit

Daily monitoring of weather and climate change, crop failure control, desertification and deforestation observation: these are just a few examples of the uses for the unique image data delivered by Proba-V from an altitude of 820 kilometers and accessed by approximately 10,000 registered users worldwide. ‘V’ stands for vegetation and refers to the environmentally focused mission of the miniature satellite, which was launched into orbit in 2013 by the European Space Agency (ESA). Cartography, however, is not its only job.

Promising technologies on test space voyages are also aboard the refrigerator-sized satellite. Among them, the satellite communication system with a gallium nitride (GaN) amplifier of German origin has raised high hopes for optimal image transmission to its Belgian ground station in the X frequency band (8 GHz). “With gallium nitride as a semiconductor material, we expect a 5- to 10-fold improvement in signal strength and data trans- mission,” said Andrew Barnes, Director of the ESA project. He and a consortium of European companies and research institutes were eager to pave the way for the GaN semiconductor into space.

There are several arguments in favor of using this technology instead of existing alternatives: unlike silicon- or gallium-arsenide-based semiconductors, GaN operates reliably and in a wide frequency range up to 100 GHz – even at high voltages and temperatures. The material also enables smaller and lighter circuit generation, is radiation-resistant, and requires no active cooling.

The MMIC amplifier (Monolithic Microwave Integrated Circuit) developed by the Fraunhofer Institute for Applied Solid State Physics (IAF) in Freiburg, Germany, is able to utilize these advantages in space for the first time. The chip, just a few square millimeters in size, required an innovative package concept that was fulfilled by partners SCHOTT Electronic Packaging and Tesat-Spacecom.

They sought to develop a high-tech housing that would protect the chip while also enabling its high-frequency waves to be transmitted with necessary strength. At the same time, the housing would have to conduct heat generated inside to the outside with the highest possible efficiency so as not to impair the chip’s performance.

The multilayer housing with HTCC technology (High Temperature Cofired Ceramics) that was developed serves as a feedthrough for high-frequency waves with low attenuation while also minimizing reflection losses on the housing wall. A heat sink efficiently dissipates the heat generated inside the housing. The developers made this possible with optimal material composition and geometry that enables the IAF’s GaN MMIC to be used in the X band.

The design has now passed the practical test in space: “It met expectations. GaN is now establishing itself as a semiconductor for such packaged power amplifiers. We are already in the process of qualifying our enclosure technology for other satellites,” says Dr. Thomas Zetterer, Head of Hybrid Development at SCHOTT Electronic Packaging. ESA’s biomass mission is the next target. From 2020 onwards, it is primarily intended to measure the distribution of surface biomass in rainforests and their annual changes, providing important insights for understanding the earth’s climate. These satellite-supported radar observations in the P band (around 435 megahertz) will use GaN RF modules based on GaN power semiconductors from the German-French group United Monolithic Semiconductors (UMS) along with the housing technology from Tesat-Spacecom (Germany) and SCHOTT. Last year, Tesat’s GaN RF power modules (15 W and 80 W) were the very fi rst ones to gain complete ESA qualifi cation by standard ESCC5010 (EEE components). “A real highlight in the space components sector is that a supply chain for GaN RF modules consists exclusively of European suppliers,” mentioned Eberhard Möss, Head of Optical Modules at Tesat-Spacecom GmbH.

Improved technologies are already under discussion for future product generations with higher microwave power: “We are working on even more efficient heat sinks to increase the thermal conductivity of our housings up to 800 W/mK. This significant improvement in properties opens up a broad range of applications in communications technology because it enables higher performance ranges and longer service life,” said Michael Tratzky, Head of Hybrid Sales at SCHOTT EP.

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