Backward-Wave Oscillation Criterion in a Step-Tapered Helix Travelling-Wave Tube

Analysis of backward-wave oscillation criterion is one of the essential steps for designing a broadband travelling-wave tube (TWT) amplifier. In this paper, a methodology for the analysis of the backward-wave oscillation criterion in a helix travelling-wave tube has been proposed with emphasis on its usage as a design tool. The analysis is also extended for a slow-wave structure having distributed RF loss and a closed-form equation has been proposed for calculating the critical interaction length. The analysis is further extended for a step-tapered TWT with distributed circuit loss included in the analysis. The method is finally applied to design a typical slow-wave structure used in an X-Ku band TWT having a step-tapered output circuit.Defence Science Journal, 2009, 59(1), pp.49-54, DOI:http://dx.doi.org/10.14429/dsj.59.148