INVESTIGATION OF THE HALF-CIRCULAR HELICAL GROOVE SLOW-WAVE STRUCTURE

As a new type all-metal slow-wave structure of the millimeter wave TWT , The helical groove has a lot of advantages: large power handling cap ability, large sizes, high precision and moderate bandwidth. Of the he lical groove structure, the half-circular helical groove can achieve w ider passband than the rectangular helical groove can do. The approxim ate and much simple matching method of the fields of the half-circular structure is presented in this paper. The more general expressions of the dispersion characteristic and coupling impedence, in which the fa st-wave modes and slow-wave modes are considered simultaneously, are o btained. It is indicated from the results of the numerical calculation that choosing suitable dimensions of the structure and suppessing the backward wave osillation, this kind of slow-wave structure can operat e over 50% 'hot' relative bandwidth.