KlystronA klystron is a specialized vacuum tube (evacuated electron tube) used as an oscillator or amplifier at microwave frequencies to produce high-power radio signals.
In the klystron, an electron beam is velocity modulated (periodically bunched) to produce large amounts of power. They can produce high frequency high amplitude signals that most solid-state devices are incapable of. They are used in radar, satellite and wideband high power communication, and high- power physics (particle accelerators).
See also: Magnetron