Electromagnetic wave propagation through an azimuthally asymmetric helix slow wave structure

In the fabrication of the practical helix slow wave structure (SWS), the misalignment or the dielectric constant variation in its support is not avoidable and, thus, causing azimuthal asymmetry in the structure. Therefore, the analysis of the asymmetric structure becomes an important issue. In this study, rigorous field analysis of a general asymmetric helical SWS was done by considering the structure as a helix supported by n wedge shaped dielectric supports, enclosed in a metal envelope. To consider the angular harmonic effect, the dielectric was not smoothed out. Using the present theory, the dispersion characteristics of the asymmetric helical structure were obtained. The study of the dispersion characteristics of the asymmetric structure revealed the stopband characteristics near the pi-phase-shift point. This result was compared with that obtained from 3D FEM code, high frequency structure simulator (HFSS) and found to be in good agreement. It was also found that the asymmetry in the structure lowered the phase velocity and the cut-off frequency but increased the stopband width.