Study on Effects of Different Metallic Vane-Loaded Helix Slow-Wave Structures in Traveling-Wave Tubes
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Study on Effects of Different Metallic Vane-Loaded Helix Slow-Wave Structures in Traveling-Wave Tubes Jianhong Yang & Yong Zhang & Xueyuan Cai & Lin Li
Received: 11 August 2008 / Accepted: 17 February 2009 / Published online: 17 March 2009 # Springer Science + Business Media, LLC 2009
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. Keywords Traveling-wave tubes . Helix slow-wave structures . Metallic vanes . Phase velocity . Interaction impedance . Fourier expansions J. Yang : Y. Zhang (*) : X. Cai Institute of Microelectronics, School of Physical Science and Technology, Lanzhou University, NO. 222, South Tianshui Road, Lanzhou, Gansu Province 730000, P. R. China e-mail: [email protected] J. Yang e-mail: [email protected] X. Cai e-mail: [email protected] L. Li National Key Lab of Surface Engineering, Lanzhou Institute of Physics, P.O. BOX 94, Lanzhou, Gansu Province 730000, P. R. China e-mail: [email protected]
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J Infrared Milli Terahz Waves (2009) 30:611–621
1 Introduction Helix slow-wave structures (SWSs) find applications as RF interaction structures in traveling-wave tubes (TWTs), which are widely employed in the fields of radars, telecommunications and electronic warfare. To obtain excellent helix dispersion characteristics, the practices have been to load the anisotropic dielectric support rods and metallic vanes. Many studies on the evaluation of rod effects on helix SWS performances were presented in the past [1–10]. They used the various approximated methods to account for the highly non-homogeneous exterior medium, ranging from the simple averaging or “smearing” of dielectric evenly over the entire exterior, to more sophisticated approaches in which the averaging is done in the azimuthal but not in the radial direction [1–5]. Furthermore, the introduction of three-dimensional electromagnetic simulators, based on
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