- A microwave tube that can be used for amplification or oscillation, and which features low noise, high gain, and a wide bandwidth. In such a tube, an electron beam produced by an electron gun interacts with a microwave signal which travels along a slow-wave structure, so that they move in approximate synchronism. This facilitates the transfer of energy from the electron stream to the microwave signal, thus providing gain. The output is taken from, or near, the collector. A backward wave oscillator is a type of traveling wave tube in which the power transfer results in oscillation. Used, for instance, in satellite and wireless communications, and in radars. Its abbreviation is TWT.