A type of vacuum tube used as the frequency source in microwave ovens, radar systems and other high-power microwave circuits. In radar, magnetrons can be used as the signal source to feed the power stage of the radar transmitter, typically a klystron tube.

A magnetron is a type of diode vacuum tube in which the filament also serves as the cathode. Rather than being used as a diode, the physical structure of the elements causes the magnetron to act as an oscillator in the UHF or microwave frequency ranges. This is accomplished through the placement of permanent magnets within a series of resonating chambers that are tuned to the center frequency of the oscillation. These resonating chambers comprise the anode of the magnetron.

In operation, as the electrons are released from the cathode, they are directed toward the anode. However, since the electrons are influenced by the magnets in the resonant cavities, they flow circularly through the resonant chambers and set up an oscillation based upon their speed through the chambers. One or more chambers contain collecting antennas that let the generated RF signal flow outside the tube. See klystron and diode.