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General Info

The Concept

With the increased usage of satellite communication systems, high efficiency and high output power amplifiers have been required for satellite transponders and they will be also demanded in the future. Traditionally, travelling wave tube amplifiers have been widely used for such applications due to their high output power levels and good power added efficiency. Nevertheless, a TWTA needs an extremely high voltage, and its reliability is considered not ideal as a result of the hot electrons in the vacuum tube. Due to these reasons, the solid-state power amplifier (SSPA) is often considered to be a solution.

In the case of Galileo system, the Full Operational Capability (FOC) Galileo satellites currently under development make use of TWTAs to provide an output power of nearly 200W at E1 band. However, the next generation of Galileo satellites will require higher output powers, around 300 W, what implies a challenge in the design and implementation of the high power amplifier.  With the enhancement of output power clearly there will be an increase in the thermal dissipation of the amplification stage, therefore the efficiency of power amplification systems for space-borne applications has to be optimized. All these challenging requirements can be satisfied by using GaN technology. At L-band, efficiency of GaN SSPA in spacecraft is similar to efficiency of TWTAs but GaN SSPA requires twice smaller area than TWTAs which leads to a 2.5 timer lower weight.

The aim of SLOGAN project is to design, develop and implement a GaN SSPA engineering qualification model (EQM) for the next generation of Galileo satellites. The development of this project will also open the door to a great variety of applications in which GaN technology will offer clear advantages over current solutions.

 

 

 GaN Technology

Gallium Nitride is a very hard mechanically stable wide bandgap semiconductor material, with high heat capacity and thermal conductivity. GaN devices offer high output power with small physical volume and high efficiency. Due to these reasons, this technology is the best candidate for microwave applications like RF power amplifiers. Up to now, in practice, when high output power is required only TWTAs are adopted since SSPA, based on other technologies such as GaAs or InP, do not achieve the same power levels. However, GaN technology provides better efficiency, higher gain, higher operating voltage, higher bandgap and higher maximum temperature, compared to these technologies.

GaN devices will have inherent high breakdown voltage capability, and they can also operate at higher bias voltages, which are closer to current standard satellite platforms bus voltages, leading to a simplified and cheaper power supply, with better overall efficiency. Moreover, GaN is able to withstand higher maximum junction temperatures than GaAs, which should imply good reliability and high power handling capability.

Due to all these advantages GaN technology developments are on-going in Europe. In this line, over the last years the focus in Europe has strongly shifted from GaAs technology to GaN-based devices and a large community including Academia, Industry and National research institutes have put all their effort in the development of this competitive technology.

 

SLOGAN Challenges

The aim of SLOGAN is to develop and test a space qualified SSPA EQM based on GaN EU technology for Galileo applications. Space applications entail conflicting constraints and very demanding performance due to the variations, as well as strict size, weight and reliability specifications. GaN technology features outstanding physical properties such as high bandgap and high breakdown field which makes GaN almost ideal for several applications on board satellite payloads.

SLOGAN project gathers several technical challenges related with the development of very high RF power amplifier and its space environment qualification. The very high output power, group delay, undesired oscillation, linearity and thermal dissipation are some of the considerations which should be taken into account during the design stage of the amplifier.