The analysis of the half-circular helical groove slow wave system

As a new type of all-metal slow-wave structures for millimeter wave TWTs, the helical groove circuits has some peculiarities: good thermal conductivity, large size and moderate bandwidth. Moreover, the half-circular helical groove structure has a wider bandwidth than the rectangular one. In this paper, using an approximate and much simpler field-matching method, the general expressions of the dispersion characteristic and the coupling impedance are obtained, in which the fast-wave and the slow-wave are simultaneously taken into account. The results of numerical calculation of the dispersion equation show that the dispersion curve is agreement with the one given by Bunch et al. (1987).