Design study of planar output-cavities for deflection modulated electron vacuum tubes

Searching for new ways to generate high power microwaves with frequencies between 10 and 90 GHz, deflection modulated vacuum tubes have been under investigation in our institute in the last years. Some of the advantages we expect are reduced space charge forces, higher linearity, easier cooling and a simpler design of depressed collectors. One of the most important parts concerning the efficiency of such a device is the output cavity, which transforms the high kinetic energy of the beam to microwave power. In view of frequencies as high as 90 GHz and dimensions in the micrometer range, we have concentrated on planar structures which can be easily realized using technologies like deep x-ray lithography (LIGA). For reliable numerical results we used the 3D electromagnetic particle-in-cell code GdfidL, originally developed in our institute and improved over several years (www.gdfidl.de).