High-frequency characteristics of free rectangular helical slow-wave structure

Based on sheath model, high-frequency characteristics including dispersion properties and coupling impedance of rectangular helix structure are derived by using field-matching method combining with integral boundary conditions. The numerical results, which are generally based on approximation approach, agree well with the results obtained by three-dimensional electromagnetic simulation software. Only when the aspect ratio of rectangular cross-section is larger than 4, the influence of the section width on the high-frequency characteristics can be neglected. Moreover, changing the pitch and dimensions of rectangular cross-section can improve the dispersion characteristics and the coupling impedance.