Two Cavity Klystron

In a two-cavity klystron amplifier, the input signal is coupled into the input cavity and the rf voltage developed across the cavity gap velocity modulates the electron beam. The output cavity is separated by a drift tube whose length is designed to provide optimum bunching of electrons at the output cavity. These bunches of electrons induce an rf current in the output cavity which is then coupled out.

A two-cavity klystron can also be constructed as an oscillator. Essentially the only difference between this and a two-cavity klystron amplifier is that the oscillator's cavities are constructed in such a way as to allow feedback from the output cavity to the input cavity. These can generate higher power levels than reflex klystrons.

Multi-cavity klystron

Multi-cavity klystrons (e.g. VA806V) have additional 'idler' cavities between the input and output cavities and these enhance the velocity modulation of the beam as they cause further acceleration or retardation of the beam.

Reflex klystron

In a reflex klystron (e.g. VA222F) there is just one cavity followed by a reflector that returns the beam back through the cavity. By optimising the phase of these returned electrons the device will oscillate at the cavity frequency.

Extended interaction klystron

In an extended interaction klystron, one or more of the single cavities of the conventional klystron are replaced by structures containing two or more interaction gaps. These are coupled both to the beam and also to each other electromagnetically.