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A 30W (peak) S-band helix travelling wave tube (TWT) has been designed and developed. Specialised techniques for the fabrication of gridded gun, rf attenuators and stainless steel to alumina sealing were developed. A number of tubes were successfully fabricated, processed and tested to check the reproducibility of rf output characteristics. The hot test results were found comparable with the predicted results. Computer aided design packages were used to validate the design of the vital components and predict the performance of the TWT.

The basic design of a TWT is obtained in stages for the given design parameters in respect of bandwidth (BW), gain, output power, efficiency, signal to noise ratio, and AM-to-PM conversion coefficient using analytical methods or available database. The final design is achieved by optimization, using computer-aided design (CAD) packages for individual sections.Generally, one may choose to first proceed with the design of slow-wave structure (SWS). The type and geometry of SWS is decided by the dispersion, which decides the BW, and interaction impedance, which decides the gain. Initial estimates of helix radius and pitch are first made on the basis of helix voltage and dielectric loading factor. At the initial stage, small signal model is used to check the parameters of the SWS, which are then optimized using the large signal model of beam-wave interaction.In the second stage, the basic design of electron gun is carried out using simple Pierce synthesis techniques. This is then optimised using electron gun ...

Vane-loaded slow-wave structures (SWS) for travelling-wave tubes (TWT) have been designed using rigorous model of Kravchenko et al [1] and a recently proposed MINV (modified infinite number of vanes) model [2], Two different SWS with six, and nine vanes respectively have been optimised to give a flat dispersion characteristic over about two octaves in S-C band by varying the radial penetration and angular thickness of the vanes. The dispersion characteristics of the cold test models of the two structures have been experimentally measured using the perturbation technique over 2–7 GHz frequency range. The comparison of the results of theoretical MINV and Kravchenko's models with the experimental results indicate that a reasonable prediction of dispersion characteristics can be made with the simpler MINV model in place of using Kravchenko's model, which is based on rigorous field analysis.