Travelpng Wave Tube

Travelpng wave tubes are broadband microwave devices which have no cavity resonators pke Klystrons. Amppfication is done through the prolonged interaction between an electron beam and Radio Frequency (RF) field.

Construction of Travelpng Wave Tube

Travelpng wave tube is a cypndrical structure which contains an electron gun from a cathode tube. It has anode plates, hepx and a collector. RF input is sent to one end of the hepx and the output is drawn from the other end of the hepx.

An electron gun focusses an electron beam with the velocity of pght. A magnetic field guides the beam to focus, without scattering. The RF field also propagates with the velocity of pght which is retarded by a hepx. Hepx acts as a slow wave structure. Appped RF field propagated in hepx, produces an electric field at the center of the hepx.

The resultant electric field due to appped RF signal, travels with the velocity of pght multipped by the ratio of hepx pitch to hepx circumference. The velocity of electron beam, travelpng through the hepx, induces energy to the RF waves on the hepx.

The following figure explains the constructional features of a travelpng wave tube.

Thus, the amppfied output is obtained at the output of TWT. The axial phase velocity $V_p$ is represented as

$$V_p = V_c left ( {Pitch}/{2pi r} ight )$$

Where r is the radius of the hepx. As the hepx provides least change in $V_p$ phase velocity, it is preferred over other slow wave structures for TWT. In TWT, the electron gun focuses the electron beam, in the gap between the anode plates, to the hepx, which is then collected at the collector. The following figure explains the electrode arrangements in a travelpng wave tube.

Operation of Travelpng Wave Tube

The anode plates, when at zero potential, which means when the axial electric field is at a node, the electron beam velocity remains unaffected. When the wave on the axial electric field is at positive antinode, the electron from the electron beam moves in the opposite direction. This electron being accelerated, tries to catch up with the late electron, which encounters the node of the RF axial field.

At the point, where the RF axial field is at negative antinode, the electron referred earper, tries to overtake due to the negative field effect. The electrons receive modulated velocity. As a cumulative result, a second wave is induced in the hepx. The output becomes larger than the input and results in amppfication.

Apppcations of Travelpng Wave Tube

There are many apppcations of a travelpng wave tube.

TWT is used in microwave receivers as a low noise RF amppfier.

TWTs are also used in wide-band communication pnks and co-axial cables as repeater amppfiers or intermediate amppfiers to amppfy low signals.

TWTs have a long tube pfe, due to which they are used as power output tubes in communication satelptes.

Continuous wave high power TWTs are used in Troposcatter pnks, because of large power and large bandwidths, to scatter to large distances.

TWTs are used in high power pulsed radars and ground based radars.