Traveling-wave tube

A second directional coupler, positioned near the collector, receives an amplified version of the input signal from the far end of the RF circuit.

The coupled-cavity TWT overcomes this limit by replacing the helix with a series of coupled cavities arranged axially along the beam.

A TWT integrated with a regulated power supply and protection circuits is referred to as a traveling-wave-tube amplifier[8] (abbreviated TWTA and often pronounced "TWEET-uh").

The bandwidth of a broadband TWTA can be as high as one octave,[citation needed] although tuned (narrowband) versions exist; operating frequencies range from 300 MHz to 50 GHz.

TWTAs using a coupled cavity TWT can achieve 15 kW output power, but at the expense of narrower bandwidth.

The original design and prototype of the TWT was done by Andrei "Andy" Haeff c. 1931 while he was working as a doctoral student at the Kellogg Radiation Laboratory at Caltech.

In addition, Nils Lindenblad, working at RCA (Radio Corporation of America) in the USA also filed a patent for a device in May 1940[11] that was remarkably similar to Kompfner's TWT.

These configuration changes resulted in much greater wave amplification than Haeff's design as they relied on the physical principles of velocity modulation and electron bunching.

[16][17][18] On July 10, 1962, the first communications satellite, Telstar 1, was launched with a 2 W, 4 GHz RCA-designed TWT transponder used for transmitting RF signals to Earth stations.

Syncom 2 was successfully launched into geosynchronous orbit on July 26, 1963, with two 2 W, 1850 MHz Hughes-designed TWT transponders — one active and one spare.

[19][20] TWTAs are commonly used as amplifiers in satellite transponders, where the input signal is very weak and the output needs to be high power.

[21] TWTAs used in satellite communications are considered as reliable choices and tend to live beyond their expected lifetime of 15-20 years.

[23] In such applications, a control grid is typically introduced between the TWT's electron gun and slow-wave structure to allow pulsed operation.

TWTAs have found applications in a number of spacecraft, including all five of the space probes that have achieved the escape velocity to leave the Solar System.

[24][25] For example, dual redundant 12-watt X-band TWTAs are mounted on the body under the dish of the New Horizons spacecraft,[26] which visited Pluto in 2015, then Kuiper belt object 486958 Arrokoth in 2019 to return data at a distance of 43.4 AU from the Sun.