A type of vacuum tube used as an amplifier and/or oscillator for UHF and microwave signals. It is typically used as a high-power frequency source in such applications as particle accelerators, UHF TV transmission and satellite earth stations. The klystron was invented at Stanford University in 1937 and originally used as the oscillator in radar receivers during World War II.

A klystron tube makes use of speed-controlled streams of electrons that pass through a resonating cavity. Electrons in a klystron are accelerated to a controlled speed by the application of several hundred volts. As the electrons leave the heated cathode of the tube, they are directed through a narrow gap into a resonating chamber, where they are acted upon by an RF signal. The electrons bunch together and are directed into one or more additional chambers that are tuned at or near the tube's operating frequency. Strong RF fields are induced in the chambers as the electron bunches give up energy. These fields are ultimately collected at the output resonating chamber. See magnetron and diode.