Introduction

Abstract

In recent years there has been a fast growth in the demand for communication systems. Radios, phones or a TV sets have for a long time been an integral part of the everyday life but there are many others, such as wireless phones, which are climbing very rapidly to the top place held by the former three. It is sufficient to think what benefit an interactive TV combined with a personal computer would be to the user, in order to have an idea of the demands on the communication networks. The fact that within this framework, audio as well as video information will be transmitted in both directions, pushes the frequency bandwidth, and thus the operating frequency, to new limits. In most of these systems the information is carried by radiation at microwave or millimeter wave frequencies. Although for portable devices the solid state technology has a substantial advantage over the vacuum electronics due to its compact systems, ground stations will still play an important role in long distance transmission. Therefore they will require new vacuum tubes which will operate at frequencies and power levels much higher than those existing today.