Backward wave oscillator (BWO) is a microwave continuous wave (CW) oscillator with excellent tuning capability and frequency coverage range. BWO is similar in construction and operates on the same principle of electron beam-RF field interconnection,generally employing a helical slow wave structure.It can be thought of as a short,thick TWT.
Operation:
The electron beam from the electron-gun cathode is focused by an axial magnetic field.If transients have resulted in starting RF oscillation,these travel through the helix and interact with electron beam.Bunching takes place increasing in completeness from the cathode to the collector and interchange of energy between the electron beam and the RF wave occurs exactly in the same way as in TWT. since BWO does not have an attenuator,there will be oscillation due to reflection from an imperfectly terminated collector end of the helix.The reflected wave results in a backward wave.
Operation:
The electron beam from the electron-gun cathode is focused by an axial magnetic field.If transients have resulted in starting RF oscillation,these travel through the helix and interact with electron beam.Bunching takes place increasing in completeness from the cathode to the collector and interchange of energy between the electron beam and the RF wave occurs exactly in the same way as in TWT. since BWO does not have an attenuator,there will be oscillation due to reflection from an imperfectly terminated collector end of the helix.The reflected wave results in a backward wave.
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