The Wave Picture of Microwave Tubes

There are many different ways in which one can make a valid analysis of the low-level or small-signal behavior of the many types of microwave tubes which use long electron beams. Which way one should choose depends partly on one's purpose in making the analysis, and partly on the particular problem to be solved. All of these analyses lead at some point to waves or modes of propagation: waves which travel along an electron stream, along a circuit, or along the two together; waves which are unattenuated or which increase or decrease with distance. Sometimes, the analysis starts out with electron current, electron velocity and circuit dimensions as the fundamental physical quantities, just as network analysis can start out with inductance, capacitance and resistance. However, an analysis can start out instead with waves, their propagation constants and their characteristic impedances as the fundamental physical bases of the analysis. We might argue that as we are to end with waves, we may well start with waves. As it turns out, the picture of the operation of various tubes in terms of waves is simple and pleasing. It is the purpose of this paper to present a picture of the operation of microwave tubes in terms of waves. This may be of some interest to those outside of the tube field, in that it gives an account of many recent devices. For experts in the field it can serve as an introduction to a method of analysis which is fairly recent and which may be unfamiliar. 1343