Study On Ka-band Novel Folded Double-ridged Traveling-wave Tube

Millimeter wave traveling wave tube has advantages of short wave length、widefrequency bandwidth、narrow wave beam、small affections by climate etc. It is widelyused in the military and the national economy. As the core component of the travelingwave tube, slow-wave system’s performance directly determines the developing level ofthe traveling wave tube. Helix traveling wave tube has a very wide bandwidth, but itspower capacity is very small. Inversely, coupled-cavity TWT has a high power capacity,but its bandwidth is very narrow. Folded double-ridged waveguide TWT, as a new typeof slow-wave structure, has a wide bandwidth, but lower coupling impedance, whichlimits the amplification of the microwave energy.In this thesis, based on the investigation of a Ka-band folded double-ridgewaveguide traveling wave tube, we have made detailed studies on two new tortuousdouble-ridged waveguide. For example, simulation of high-frequency characteristicssuch as dispersion and coupling impedance, analysis of beam-wave interaction usingthree-dimensional particle simulation software CST. The research shows that the twonew structures’ coupling impedance is higher than the conventional structure of thesame size and their frequency bandwidth is the same as the conventional one. To furtherimprove the output power of the TWT, based on the folded double-ridged structure, weconsidered using sheet beam electron instead of the traditional round one to participatein the beam-wave interaction process. We take ka-band as an example.1. Folded double-ridge waveguide. The theory of high-frequency characteristics ofthis structure is described, and the dispersion、coupling impedance character andinfections of various dimentions on its high frequency characteristics are investigated byHFSS.2. Single groove-loaded folded double-ridged waveguide. It produces higher outputpower at33GHz in Ka band than the normal folded double-ridged structure throughsimulation, together with larger gain and electronic efficiency. Its3-dB gain bandwidthis about6GHz, and output power is up to50W from29GHz to39GHz. In addition,compared to the conventional structure, the groove-loaded folded double-ridged can be saturated within a shorter interaction distance.3. Double groove-loaded folded double-ridged waveguide. It has an extremely flatdispersion curve but higher coupling impedance at32GHz and subsequently producesconsiderably higher power and efficiency comparing to the conventional waveguide, thestructure has an extremely flat dispersion curve and higher coupling impedance. To getthe same power output, the double groove-loaded folded double-ridged waveguiderequires lower beam voltage than the single groove-loaded structure through CSTsimulation under the condition of same circuit length. So the double one can reduce thevoltage applied to the electron gun. However, the double one’s3-dB gain bandwidth isapproximately4.5GHz, which is narrower than the single ones’. We can see thatgroove-loaded waveguide obtain higher output power at the cost of reducing bandwidth.From the foregoing, those new TWT have a very good potential for development indeveloping miniaturized high-power millimeter wave traveling wave tube.