Review of Flexible TWTs for Satellite Systems
Andre, F.; Boone, Ph.; Bosch, E.; Siefke, A.; Wohland, R.; Wunsche, T.
Thales Electron Devices

Thales Electron Devices introduced several years ago the new feature of power flexibility to its products in order to best fit the need of its customers. Power flexibity means that the saturated power of the TWT can be changed at any time by changing the anode voltage that controls the electron beam current in the TWT. The advantage of power flexibility over backing-off the amplifier is that the DC consumption and the dissipation are greatly reduced. For example when the power of the TWT is reduced by 3 dB, the saving on the power consumption and the dissipation is 35%. The range of power flexibility is at least 4 dB with very little efficiency degradation on the first 3 dB.

Power flexibility has now become a reality with the first fligthset of flexible TWTAs delivered for the HYLAS satellite and other satellite systems, even for navigation, are showing interest in this concept. TED is proposing flexibility on most of its TWTs, in S, L, Ku and Ka band. EPC manufacturers have also introduced a telecommand circuitry into their EPC to control the TWT power. Another interesting architecture for power flexibility is the multiport power amplifier (MPA or Butler matrix). The TWT phase and gain stability are very important in the case of the MPA, especially in Ka band, and we have measured and analyzed them over temperature and aging in Ka band. Small matrices of 2 and 4 LTWTAs were also tested.

This presentation will review the present status of flexible TWTs in Ku and Ka band which were developped under ESA funding.