Microwave tubes operate at frequencies from 300 MHz to 300 GHz with output power ranging from 10 mW to a few hundred watts. The operating principle of microwave tubes is based on velocity modulation of electrons. The velocity-modulation concept is used to prevent the problems caused due to transit-time effects that are encountered in conventional tubes. A long transit time is used very effectively in microwave tubes in the conversion of dc power to RF power. By using the resonant cavities in the microwave tubes, and the velocity modulation of electrons, the power can be interchanged.
In conventional vacuum tubes, the modulation of electron beam can be done by altering the number of electrons. The microwave ...