Study on Effects of Different Metallic Vane-Loaded Helix Slow-Wave Structures in Traveling-Wave Tubes

Abstract

The effects of different metallic vane-loaded helix slow-wave structures of a traveling-wave tube are proposed based on the analysis of the Fourier expansions of the exterior region with metallic vanes. The influences of the metallic vanes dimensions on the phase velocity and interaction impedance are considered in detail. The computed data is compared with the reference data in the 0−16 GHz frequency range with a good consistency. The analytical results reveal that the method of using Fourier expansions can contribute effectively to the reducing of the error between the theoretical and experimented data (around 1.2%). By analyzing the computed results, the performances of the helix slowwave structure, with T-shaped metallic vanes are superior to the sector-shaped with the same designed parameters. Adjustments can be made to the outer radius of T-shaped metallic vanes which then control the dispersion relation showing either negative or positive, and it is similar to sector-shaped vanes by adjusting its inner radius. And with increasing the distance between the helix and metallic vanes, the dispersion characteristics and interaction impedance of the helix slow-wave structure with T-shaped/sector-shaped metallic vane are all improved.

Vane-Loaded Planar Helix Slow-Wave Structure for Application in Broadband Traveling-Wave Tubes

“…4(a). As observed in [7], the addition of vanes to the circular helix can produce a flatter phase velocity versus frequency curve with only a moderate reduction of the interaction impedance and the T-shaped vanes provide flatter dispersion characteristics.…”

“…The circular helix has been a very popular SWS for TWTs since it offers very broadband beam-wave interaction and many studies have been carried out for its dispersion shaping, including that of [3]- [6], as well as more recent ones [7]- [9]. The dispersion-shaping techniques that have been studied for the circular helix include bringing the metal shield close to the helix, reducing the dielectric constant of the rods that support the helix inside the shield, incorporating metal vanes of different shapes in the shield, and metal coating the dielectric support rods.…”

Planar helix slow-wave structure with straight-edge connections in the presence of coplanar ground planes

“…The dispersion characteristic of the SWS is the main factor which determines the operating characteristics such as bandwidth of a TWT [5]. Many dispersion shaping methods such as different shapes of metal vanes and dielectric support rods have been introduced for the TWTs based on circular helix SWS [6]- [10] to obtain multi-octave bandwidth while keeping high value of interaction impedance. For PH-SEC in the presence of multilayer dielectric substrates, the effects of variation in aspect ratio, metal shield distance and dielectric constant of the substrate have been studied to obtain flat phase velocity versus frequency curve [11].…”

A Simple Analysis of Helical Slow-Wave Structure Loaded by Dielectric Embedded Metal Segments for Wideband Traveling-Wave Tubes

“…The metal segments/vanes projecting radially inwards from the metal envelope causes anisotropic loading of the SWS [8][9][10]. Both inhomogeneous and anisotropic loadings can be used to control the dispersion of the helical SWS [8][9][10][11][12][13][14][15][16]. Wideband high gain helix TWTs utilize both types of loading separately as well as simultaneously [9][10][11][12][13].…”