Analysis Of The Circular-Arc-Shaped Helical Groove Slow-Wave Structure

This paper concerns a new circular-are-shaped helical groove all-metal structure, and emphasizes the propagation characteristics of the slow wave. By using approximate field-matching conditions, the dispersion equation and the coupling impedance of this circuit are obtained. The dispersion curves and coupling impedances of the fundamental wave and some harmonics are calculated and the influences of various circuit dimensions are discussed. The calculation results show that the bandwidth can be improved by increasing the are angle or decreasing the pitch of the structure; a 50% bandwidth is achieved by deviating the phase velocity within +/-5%. As a new slow-wave structure for a travelling wave tube, this circuit has an attractive feature, namely the bandwidth is broad while power capacity is high.