SCHOTT solutions no. 2/2013 > Electronic components

Smaller than one cubic meter, Proba-V is one of ESA’s minisatellites tasked with a big mission: to completely map Earth’s land cover and vegetation growth every two days. Photo: ESA

Revolutionizing Communication in Space

Satellite ”Proba-V” debuts new semiconductor amplification technology based on a hermetic, high-power RF package.

Dr. Haike Frank

Proba-V, which went into orbit in May 2013, is the newest member to a family of smaller missions by the European Space Agency (ESA). While this mini-satellite’s main task is to monitor Earth’s global vegetation, hence the letter V in its name, it also carries a number of technology demonstration payloads, giving promising European technologies flight experience and an early chance to be tested in space. One such example of a guest payload is high-power gallium nitride technology.

The satellite is equipped with a gallium nitride amplifier within its communication system for transmitting to Earth photos taken at a height of roughly 800 km in X band at 8 GHz. “Gallium nitride has the potential to revolutionize communication in space; it is an extremely promising material,” explains ESA’s Andrew Barnes, heading this technology project. ”We expect signal strength and data transmission to improve five- to ten-fold, and are eagerly awaiting the results of this first practical test in space.”

ESA commissioned a consortium of European companies and research institutions to develop a space-quality gallium nitride supply chain, called the GaN Reliablity Enhancement and Technology Transfer Initiative (GREAT2). ”GaN could in the future enable more efficient solar panels and satellite power converters, but to begin with the GREAT2 consortium has focused on communications systems,” says Barnes.
SCHOTT and Tesat-Spacecom have developed a completely new type of hermetic packaging (picture left) for the gallium nitride power amplifier in the ESA satellite Proba-V (in the middle). The mapping (right) includes the daily tracking of weather activity, monitoring crop failures, documenting inland water resources and watching over the continuous spread of deserts and deforestation. Foto left: tesat-spacecom, Photo center: ESA, Source right: ESA
Proba-V’s GaN Monolithic Microwave Integrated Circuit (MMIC) amplifier is an initial prototype, developed by the Fraunhofer Institute for Applied Solid State Physics in Freiburg, Germany. The MMIC amplifier chip delivers its performance on a surface area only a few square millimeters in size and therefore requires innovative hermetically-sealed packaging concepts developed by SCHOTT Electronic Packaging and Tesat-Spacecom in a joint project. ”We had two major challenges: keeping insertion loss and reflection of the high frequency waves at a minimum and achieving high thermal conductivity by creating an optimal heat sink in the housing,” recalls Dr. Thomas Zetterer, Development Engineer at SCHOTT Electronic Packaging.

Thanks to the innovative design of the hermetically sealed HTCC multilayer ceramics as high-frequency feedthroughs, the high-frequency waves are able to pass through the wall of the housing with very low attenuation. In addition, the reflection losses of the high-frequency waves along the housing wall are also minimized. “Simulations of electromagnetic waves have enabled us to determine the best possible geometries and designs for this special type of feedthrough in close coordination with manufacturing technology,” adds Zetterer. The second important property of the package is the high thermal conductivity of its base that allows for the dissipation of the heat generated inside the MMIC amplifier. To achieve this, the development teams at SCHOTT and Tesat-Spacecom came up with just the right material composition and geometry for a heat sink for this particular application, keeping in mind the requirements for the highest reliability of the system in space.

Materials and material compounds that allow for even higher thermal connectivity still need to be developed in the near future and tested for use in applications with even higher microwave power. ”Working together with SCHOTT enables us to obtain the innovative high thermal conductivity packages that are urgently needed for future gallium nitride amplifiers,” explains Eberhard Möss, Group Leader at Tesat-Spacecom. <

What Is Gallium Nitride?