A twowave theory of travelingwave tubes and backwardwave oscillations
Abstract
Starting from Pierce's smallsignal travelingwave tube (TWT) equations, a twowave theory for complicated TWTs and backwardwave oscillations (BWOs) is developed. Explicit gain expressions for TWTs with severs and velocity tapers are given. A detailed treatment is given of a backwardwave amplification structure with a singlestep velocity taper in the center. The BWO start oscillation current is calculated as a function of the taper strength. The efficiency of a step velocity taper as a remedy for backwardwave oscillations in the higher passbands of a TWT is then analyzed. It is shown that a suitable taper can increase the start oscillation current by more than a factor of 10 without adverse effects on the TWT performance if the backward wave coupling impedance is low. A tube with a weak linear taper is analyzed by a perturbation technique and it is found that there is no significant difference between the start oscillation currents for tubes with weak linear or abrupt tapers of comparable strengths.
 Publication:

IEEE Transactions on Electron Devices
 Pub Date:
 October 1975
 DOI:
 10.1109/TED.1975.18236
 Bibcode:
 1975ITED...22..869N
 Keywords:

 Backward Waves;
 Microwave Oscillators;
 Performance Prediction;
 Traveling Wave Tubes;
 Wave Interaction;
 Coupling Circuits;
 Electrical Impedance;
 Electromagnetic Interactions;
 Energy Conversion Efficiency;
 Perturbation Theory;
 Space Charge;
 Tapering;
 Communications and Radar