What is "traveling-wave tube"

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.{{cite book

| last1 = Whitaker
| first1 = Jerry C.
| title = The RF Transmission Systems Handbook
| publisher = CRC Press
| date = 2002
| location =
| pages = 8.14–8.16
| language =
| url = http://books.google.com/books?id=G5UHVIqEWdQC&pg=SA8-PA14&dq=%22traveling+wave+tube
| doi =
| id =
| isbn = 1420041134
}}

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.

TWTs account for over 50% of the sales volume of all microwave vacuum tubes. They are widely used as the power amplifiers and oscillators in radar systems, communication satellite and spacecraft transmitters, and electronic warfare systems.

A TWT has sometimes been referred to as a traveling-wave amplifier tube (TWAT), although this term was never widely adopted. "TWT" has been pronounced by engineers as "twit", and "TWTA" as "tweeta".