A
traveling-wave tube (
TWT) is a specialized
vacuum tube that is used in
electronics to amplify
radio frequency (RF) signals in the
microwave range. The TWT belongs to a category of "linear beam" tubes, such as the
klystron, in which the radio wave is amplified by absorbing power from a beam of
electrons as it passes down the tube. Although there are various types of TWT, two major categories are:
- Helix TWT
- In which the radio waves interact with the electron beam while traveling down a wire helix which surrounds the beam. These have wide bandwidth, but output power is limited to a few hundred watts.
- Coupled cavity TWT
- In which the radio wave interacts with the beam in a series of cavity resonators through which the beam passes. These function as narrowband power amplifiers.
A major advantage of the TWT over some other microwave tubes is its ability to amplify a wide range of
frequencies, a wide
bandwidth. The bandwidth of the helix TWT can be as high as two
octaves, while the cavity versions have bandwidths of 10–20%. Operating frequencies range from 300 MHz to 50 GHz. The power gain of the tube is on the order of 40 to 70
decibels, and output power ranges from a few watts to
megawatts.