Study On The Characteristics Of Vane - Loaded Helical Slow Wave Structure

The broad-band and high power traveling-wave tube(TWT) is very important in the modern military equipments such as Radar > jammer etc. The Helical slow-wave structures find wide application as RF interaction structures in the traveling-wave tubes. It has many advantages such as the simple structure, excellent dispersion characteristic and the high interaction impedance.First of all, the field theory based on the sheath model is used to study the characteristic of the helix in this dissertation. An actual helix is regarded as the helical conductive cylinder. By means of this model, the utility dispersion equation, the interaction impedance and the attenuation constant are obtained.Besides, the tape helix model is suggested too. In this model, the fields of the inside and outside helix have been expanded by the space harmonics, and then the expanded coefficient can be sovled from the given tape current utlizing the condition on boundary. Moreover, the dispersion equations, as well as the interaction impedance and the attenuation are worked out."Helix", a CAD software on the helical slow-wave structure is developed by the derived equations and the visual technology under Visual C++, and it is used successfully in TWT CAD software packet. Some typical helical slow-wave structures of TWT are calculated by the derived equations. The calculating results on the sheath and tape model are compared with those of the measurements. It is shown that the tape helix model is better than the sheath model under same conditions. The influence on dispersion characteristic is analyzed for two types of hypothesis current, the different permittivity of the dielectric support and the different radius of the metal envelope.The dispersion characteristic of a vane-loaded helical slow-wave structure isinvestigated experimentally by the travelling wave method. The "cold" test results are in good agreement with the theoretical results.