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A total full Qualification sequence is in progress with In satellite systems, on-board repeaters are required to several prototypes under test. It will be completed in Q1 provide higher and higher levels of RF power. 2011. This Qualification phase includes also several Specifically in Ka band, a substantial increase of RF power margin severe tests to demonstrate the tube reliability and is requested in some applications like HDTV and internet the design margins versus typical standard requirements. to improve the available data rate.Production of this high power tube could start mid 2011. In order to respond to this demand, Thales Electron Devices (TED), with the support of CNES (French Space Design and Typical Figures Agency), is developing a TWT (TH4816) which delivers 170W in Ka frequency band. This paper gives the mainThe main characteristics of the 3 sub-assemblies (gun, line technical characteristics of the TH4816 design and the and collector) and housing of this TWT are the followings. main performances over the total Ka frequency band from 17.3 to 21.2 GHz.Gun With the increase of operating voltages (7500V typically for cathode voltage), the gun size has been increased to Introduction withstand 10 kV high voltage class.In order to address the global trend of RF power increase This design allows to reach more than 15 years of life time in Ka frequency band, TED is extending the current (M type cathode with limited cathode current density) with TH3990 capabilities at 135W maximum up to 170W with high reliability. the TH 4816.Optics dimensions were designed to optimize beam quality Benefiting of the TH3990 Space unrivalled experience for focusing, key parameter for high power tubes operating with high reliability proven in orbit, the TH4816 at high frequency. development phase covers the following steps:x Space qualification at sub-assembly level (including Line some margin tests), External dimensions of the delay line are the same as the x TH3990. A periodic permanent magnet stack has been was Design simulation at TWT level with breadboards to optimized in order to minimize helix current taken into achieve 170W, account the beam characteristics at the exit output of the x Engineering Models manufacturing and tests, gun. x EQM qualification, margin tests and mission profile demonstration. Electrical efficiency has been optimized (more than 63%) with high linearity performances. Instantaneous frequency bandwidth is more than 1 GHz with saturated RF gain higher than 50 dB.The RF output design is the same as the TH3990. Indeed, RF power capability of this design is well adapted to the RF power increase. It allows to keep the technological heritage.Collector A four-stage depressed collector allows to reach a global efficiency higher than 63%. Collector size is larger than the TH3990 to take into account the increase of dissipation Fig1. TH4816 (170W) with larger radiator and TH3990 and also higher voltages.978-1-4244-8660-1/11/$26.00 ©2011 IEEE 75

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