Characteristics and application of traveling wave tube
The traveling wave tube is a microwave tube that realizes the amplification function by continuously modulating the speed of the electron beam. In the traveling wave tube, the electron beam interacts with the microwave field traveling in the slow wave circuit. In the slow wave circuit of 6 to 40 wavelengths, the electron beam continuously transfers the kinetic energy to the microwave signal field, so that the signal Get zoomed in.
The characteristics of the traveling wave tube are bandwidth, high gain, large dynamic range and low noise. The bandwidth of the traveling wave tube (the frequency difference between the high and low ends of the frequency band/center frequency) can reach more than 100%, and the gain is in the range of 25 to 70 decibels. The noise figure of the low noise traveling wave tube is as low as 1 to 2 decibels.
In the traveling wave tube, the electron beam interacts with the microwave field in the slow wave circuit. The microwave field travels along the slow wave circuit. In order for the electron beam to effectively interact with the microwave field, the direct current movement speed of the electron should be slightly higher than the phase propagation speed (phase speed) of the microwave field traveling along the slow wave circuit, which is called the synchronization condition. The input microwave signal establishes a weak electromagnetic field in the slow wave circuit. After the electron beam enters the interaction area of the slow-wave circuit, it is first modulated by the velocity of the microwave field. The electrons gradually form density modulation as they continue to move forward. Most of the electrons cluster in the deceleration field, and the electrons stay in the deceleration field for a long time. Therefore, part of the kinetic energy of the electron beam is converted into the energy of the microwave field, so that the microwave signal is amplified. Under synchronized conditions, this interaction between the electron beam and the traveling microwave field continues along the entire slow-wave circuit. This is the fundamental difference between traveling wave tube and klystron in principle.