Research On Novel Helical Slow-wave Structure

Helix traveling-wave tubes (TWT) with wide-bandwidth, high power, highefficiency and high gain, which especially can be chained with solid state poweramplifier (SSPA) and electronic power conditioner (EPC) to form superior MicrowavePower Module (MPM), are attractive for many applications, such as radar, electroniccountermeasures and communication. Helix slow-wave structure (SWS) which canreduce the phase velocity of electromagnetic wave to be equal to the velocity of theelectron beam is the key component of the TWT. Because its heat dissipation capabilityis limited, the average-power of the TWT is low. As the development of the militaryelectronic technology, the helix TWTs with wider bandwidth, higher power, higherfrequency, longer life and smaller size are urgent. In this paper, analog simulation andexperimental measurement are used to study the novel helix SWS. The important worksand innovation points are listed below:1. To improve the heat dissipation capability of the helix SWS, and then enhance theaverage power of millimeter-wave TWT, the slotted helix SWS has been proposed by us.The thermal analysis model is constructed and the thermal deformation analysis is alsostudied. Our preliminary thermal analysis of this structure shows that it has better heatdissipation capability and smaller thermal deformation than those of the conventionalhelix SWS in the same conditions. The slotted helix SWS operating in the Ka band isdesigned. The model with concentrated attenuators and sever is constructed by usingCST software and the beam-wave interaction simulations of the novel slotted helixslow-wave circuit are conducted by utilizing CST Particle Studio. The results show thatthis novel circuit can produce over700W average output power in a frequency rangefrom27.5GHz to32.5GHz, the corresponding conversion efficiency and gain over19%and41.1dB. At the end of this chapter, the double-slotted helix slow-wave structure isproposed to improve the coupled impedance of the SWS whose beam-wave interactioncharacteristic is studied also.2. To overcome the difficulties of ceramic dielectric rods easily brittle and decreasethe fluctuation of gain, a kind of dielectric rods with metal inner core is proposed. Theprocess method of this kind of rods is studied, and the rods are applied in the helix SWS.The beam-wave interaction circuit of the helix SWS operating in V-band is designed. The results show that the flexibility of these rods with metal core is better than that ofthe conventional rods; therefore, they are not easily fractured. Meanwhile, the metalcore in the rod can also improve the dispersion characteristics of the helix SWS. Fromour calculations, when the designed beam voltage and beam current are set to be13.1kVand0.06A, respectively, this novel TWT can produce over80-W average output powerin a frequency range from53GHz to68GHz, and the corresponding gain and conversionefficiency can reach over39dB and10.3%.3. To solve the problem of processing and assembling difficulties, a novel windingmicrostrip meander-line SWS is proposed. The processing method of this structure isstudied and the interaction circuit of the SWS operating in the V-band is investigated.The results show that this novel winding microstrip meander-line TWT can produceover130W peak power output in a frequency range from58GHz to63GHz, thecorresponding conversion efficiency values and gain over8.2%and31.6dB.4. The slow wave circuit of octave helix TWT with T-shaped dielectric rods isdesigned. The calculated results show that the output power of fundamental wave in oneoctave band values over250W, the gain of second harmonics is lower than-7dB. Thethermal analysis and thermal stress analysis of the nonintercepting gridded electron gunmodel are studied and the assembling distance of the electron gun is also calculated.The method (magnetic field taper technology) of restraining second harmonics isproposed. The gain of second harmonics is restrained to-11.32dB, the correspondingfundamental power is over300W.5. The experimental research of the low harmonics octave TWT is carried out. Theelectronic optical sample tube and whole tube according to the designed scheme areassembled respectively. First, the flow rate experimental test in the optical sample tubehas been done. The test results show that the flow rate of the sample tube can reach to98.2%, the emission characteristics of the nonintercepting gridded electron gun is good,and the current of the control gate is only2μA. Second, the transmission property of thewhole tube is tested. At last, the hot test of the whole tube is also tested. The resultsshow that the output power of fundamental wave in one octave band values over250W,the gain of second harmonics is lower than-7dB and the electronic efficiency is over13%.