Finite Thickness Helix Slow Wave Structure

As an extremely important kind of the microwave electronic vacuum device, the high efficiency, wideband and the low noise characteristic of TWT have received people's universal attention. TWT is playing the vital role in the modern military domain, particularly in the electronic countermeasure and the satellite communication domain. As the key component of the Traveling Wave Tube (TWT), the slow-wave structure (SWS) basically determines the performance of the TWT. So, improving the performance of SWS is an important developing direction of the TWT research in order to improve the broadband characteristic and increase the operating frequency and power capacity.Helix traveling wave tube is one of the most commonly used TWTS at present. It has weak dispersion, wide bandwidth but weak heat dissipation capability. So the increasing of output power is confined. Therefore, it is an vital subject in the development of TWT that how to gain a bigger consecutive wave output power without putting any influence on the wide bandwidth characteristics in a single Helix TWT.Based on this idea,a special helix——thick tape helix SWS is analyzed in this paper. As it has bigger heat conducting capacity and thermal capacity than ordinary thin tape helix SWS, it has a potential for bigger output power.With the analytic method of the Field Theory, this paper directly gives the radial field expression of helix tape region, concludes the dispersion equation and the coupling impendence expression of thick tape helix with the helical coordinate system. The analytic theory of this structure is also obtained by using Hook's equivalent model. With a large amount of calculations, the transformation rule of the dispersion characteristic and coupling impedance of the slow-wave structure under both modals following the structural geometric size and dielectric parameters is obtained. Then, the linear beam-wave interaction theories are deduced respectively. By the numerical calculations, the relationship between the electronic beam, the structural parameters and the small signal gain is got. The method of increasing the bandwidth or gain is obtained. Several important and valuable results which bring forth new ideas are achieved and listed as the followings:1. The helix tape considering its radial thickness is analyzed in this paper. The radial field expression and dispersion equation are derived with the helical coordinate system. We discuss the effects of the helix-wire thickness on the dispersion characteristic of the helical slow-wave structure with numerical method and compare HOOK 's method with our approach. It shows that the result of our approach is closer to CST simulation.2. We obtain the beam-wave interaction linear theory of the finite thickness helical slow-wave structure and the HOOK 's method by utilizing field boundary conditions and the continuous conditions on the surface field of electron beam. The research on the linear theory indicates that the existence of the electron beam has improved the systematic dispersion characteristic. The increase of the gain can be achieved by increasing the beam current, beam radius and choosing the optimal structure parameters.Finally, a brief summary of the conclusion and deficiency about this paper has been given, the future worked emphasis and necessity has also been pointed in the last chapter.