The microwave power module (MPM) obtains the best features of solid state and vacuum electronics technology by combining a TWT, a solid state driver and their required power supplies in a single package. The leader in the manufacture of the light weight MPM is Northrop Grumman, which has produced a 220 Watt, C-Band MPM that weighs only 4.2 pounds and has a volume of 48 cubic inches. For operation at the GPS L-Band frequency, existing technology may be able to provide approximately the same power and efficiency that has been demonstrated at C-Band, but the weight of the TWT would increase significantly. The innovation proposed here is to produce an L-Band MPM with that exceeds the performance requirements of the GPS application, but containing a TWT with significantly reduced length. This would be accomplished by replacing the conventional thermionic cathode in the electron gun with a modulated field emission cathode. By launching an electron beam that is already modulated at the cathode, the length of the slow wave circuit can be significantly reduced. Furthermore, by eliminating the heater of the thermionic cathode, the TWT efficiency will be increased
Benefits: The primary cost factors in communications satellite payloads are the mass and efficiency of the power amplifiers. Typically spacecraft have a limited availability of power, and typically the power amplifiers are the largest consumer of power on board. For a commercial satellite, a seemingly small increase in efficiency may be worth millions of dollars to the system operator if it allows the spacecraft to carry even one additional revenue generating transmitter. Improvements in efficiency can translate directly into reductions in the mass of solar cells and thermal control systems. The mass and efficiency of the power amplifiers control the size of the spacecraft, and, therefore, the choice of launch vehicle.
Keywords: field emission, TWT, GPS, diamond, traveling wave tube,vacuum electronics
