Klystron

A klystron is a high-power vacuum electron-tube amplifier used in satellite communications to generate the RF output power required to overcome the large free-space and atmospheric losses on Earth–satellite links. It operates by velocity-modulating an electron beam within resonant cavities and converting the resulting bunching of electrons into amplified RF energy, making klystrons well suited to high-power, narrowband applications such as satellite uplinks and ground station transmitters.