Write short Note on backward Wave Oscillator.

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written 7.9 years ago by

teamques10 ★ 68k

Backward wave oscillator is a microwave continuous wave oscillator with excellent tunning capability & frequency coverage range.
It is BWA in which the input which is a collector end of the tube, is terminated in a resistive coating. The output power is extracted at the gun end.
Due to D.C. voltage applied to helix a transient noise signal is generated at Kf frequency which start the Rf oscillation.
This R.F. backward wave signal travel through helix and interact with the electron beam in a accumulative region and steady state oscillation is established at a particular frequency in BWO growing Kf wave travels in a direction opposite at electron beam.

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The fig. shows the several regenerative loops that functions as an amplifier with β as feedback.
Each regenerative loop functions as an amplifier as oscillator & is designed such that the phase shift around the loop is 2π radians.
When the +ve feedback takes place, The β circuit loop oscillates at the frequency at which the total delay is 2π radians.
The Rf field velocity modulates the electron beam which moves towards collector end of the tube forming a bunch.
This bunch now provided energy to the helix Rf wave in the backward wave direction.
This looping continues until there is a sufficient energy in the Rf wave.

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