High Power L-Band Travelling Wave Tubes for Navigation Systems
Dürr, W; Ehret, P; Bosch, E
Thales Electron Devices

Abstract: Today trade and industry between all continents on the world get more and more into closer interaction. Therefore all industrial nations recognized an increase of the importance to join a cooperation dealing with satellite navigation systems. A lot of different and sensitive applications will use satellite signals to calculate the exact position on the world or to have always the exact time available as high reliable standard. There are existing systems using satellites in orbit, but there is a strong technical evolution to explore new applications and higher resolution of the positioning.

To provide the signals is a technical challenge. Mainly for the space segment of a navigation system the development in the future is not easily to predict. Therefore the technology has to be well prepared for all trends in the near future. So the most important demands on the system at any time are increased resolution, high accuracy, complete coverage and extreme reliability.

Satellites are used to transmit signals for different kinds of application. Since more than 35 years the satellite operators relay on Travelling Wave Tubes (TWT). The tube technology demonstrates the highest level of reliability, flexibility and quality in hundreds of millions of accumulated operating hours in space. Travelling Wave Tubes can be used for practically unlimited range of RF power at all frequencies at a very low level of signal distortion. The power supply is also available as the experience to handle the thermal and mechanical interface.

For the space segment of positioning systems, the TWT is an ideal solution. For the navigation systems signals in the L-band between 1.15 GHz and 1.65 GHz are used. For the new generation of Navigation Systems with some new applications an increase of the output power will be needed mainly for receivers in so far non-standard or difficult environments (i.e. indoor, towns with high buildings, ...). Exact in the L-band there are tubes with an output power of 150 W operating in orbit successfully since years. The application here is direct radio broadcasting. This tube with an outstanding heritage is the basis for the L-band TWT portfolio produced by THALES Electron Devices. THALES tubes are available up to 150 W output power from 1.15 GHz 1.65 GHz. The navigation signals at 1.5 GHz requires typically higher output power, which can be offered by THALES from 1.45 GHz to 1.65 GHz up to 250 W. Sometimes there is a need of the satellite platform to reduce the thermal load coming from the amplifier. Therefore the tubes up to 150 W are also available as self radiating design which transfers the major part of the dissipated thermal energy directly into space. With the identical technology additional services in the S- or C-band can be operated.

For the in orbit validation of the European Navigation System Galileo amplifier for the signals in the frequency range between 1.15 GHz and 1.6 GHz were needed. Thales Electron Devices (TED) showed the high flexibility of the tube technology. In a very short period of time a tube was developed especially designed for the need of the first Galileo test satellite (Giove-A) with an output power at the operating point of 50 W. To reduce the total amount of amplifiers on the satellite, the tube was designed for an operation in the full band which is used for Galileo (1.15 GHz to 1.6 GHz). Since almost two years during the test phase of Giove-A the THALES tubes are providing very stable and reliable signals which demonstrate that the tube technology is an excellent solution for the signal amplification on navigation system spacecrafts.

Summary: The paper will show the actual performance data of TED’s improved L-band tubes, and will demonstrate through the obtained results that L-band TWTAs provide attractive solutions, suited for all navigation systems. But also L-band Travelling Wave Tube can provide outstanding advantages for a number of different applications. The background of this will be demonstrated in addition in the paper.