The twystron, which was used in several Marconi transmitters, is a multicavity amplifier klystron in which the output section is replaced with a system of coupled resonators. In a Twystron, the electrons emitted by the cathode first pass through the klystron resonators, where they are grouped into bunches, as in a conventional klystron; they then pass through the system of coupled resonators, where they excite a travelling wave. Upon interaction with this wave, part of the kinetic energy of the electrons is converted into microwave energy, as in a conventional travelling-wave tube. The use of coupled resonators increases the operational frequency bandwidth to 715% of the mean frequency.
Twystrons provide the broadest bandwidths of all high-pulse-power microwave devices. They are manufactured for operation in the super high-frequency (microwave) band (wavelengths from 5 to 10 cm) and have pulse power ratings of 38 Megawatts, gains of 3550 decibels, and efficiencies of 3540%. Twystrons were developed in the USA in the 1960s by Varian Associates. They are used chiefly as transmitters in high-power radar installations on land and on board ships.