Electron Ballistics in High-Frequency Fields

of high-frequency devices. Much that might otherwise be said about ultrahigh frequencies cannot be said because of secrecy requirements. However, there is considerable material which can be presented, within the limits of the necessary security regulations, which may be of interest to those who are not already well acquainted with the subject. I will, perforce, not be able to say anything specific about actual devices utilizing the principles to be discussed. Many of the ultra-high-frequency devices which have come into use during the last few years have employed electron beams of one sort or another. These devices can be analysed in any one of a number of ways. For example, we can write the equation of space-charge flow. This approach considers the electric charge as a continuous fluid subject to Poisson's equation. The small-signal theory of Peterson and Llewellyn is an example of this type of analysis. Or if we wish we can consider the various types of wave motion which can exist in a space-charge region. The space-chargewave analysis of Hahn and Ramo as applied to velocity-variation tubes is an example of this. In addition there is an electron-ballistic approach to the problem and it is with this method that we will be concerned in the present lecture. Before we become involved in the details of the analysis, we should perhaps spend a few moments considering the relationship between these various methods. If we have an interaction taking place between electric fields and moving charges, we know at once from Newton's second law that the forces acting on the electrons must of necessity be equal and opposite to those acting on the fields.