Recent theory of traveling-wave tubes: a tutorial-review

The traveling-wave tube (TWT), also known as the traveling-wave amplifier (TWA) or traveling-wave tube amplifier (TWTA), is a widely used amplifier in satellite communications and radar. An electromagnetic signal is inputted on one end of the device and is amplified over a distance until it is extracted downstream at the output. The physics behind this spatial amplification of an electromagnetic wave is predicated on the interaction of a linear DC electron beam with the surrounding circuit structure. Pierce, known as the ‘father of communications satellites,’ was the first to formulate the theory for this beam-circuit interaction, the basis of which has since been used to model other vacuum electronic devices such as free-electron lasers, gyrotrons, and Smith-Purcell radiators, just to name a few. In this paper, the traditional Pierce theory will first be briefly reviewed; the classic Pierce theory will then be extended in several directions: harmonic generation and the effect of high beam current on both the beam mode and circuit mode as well as ‘discrete effects’, giving a brief tutorial of recent theories of TWTs.