Research Of The Millimeter-wave Sheet Beam Variant Half Rectangular-ring Helix Traveling-wave Tubes

Millimeter-wave technology occupies an advantageous position in the fields of communications,imaging systems,RF astronomy,and clinical medicine.The development of millimeter-wave technology puts forward requirements for large power,high gain,and miniaturization of traveling wave tubes(TWT).Slow-wave structure(SWS)is an important place for beam-wave interaction which performance indicators play a decisive role in TWT.Coupling cavity and helix structure are two types of SWS that are widely used.The coupling cavity,as an all-metal structure with strong thermal dissipation performance,is commonly used in high-power TWT,but its working bandwidth is relatively limited.The dispersion of the helix structure is relatively flat and the bandwidth can reach more than two octaves.However,with the power increases,the current density of the cathode needs to be increased to meet the power demand.The cylindrical electron beam has a strong space charge force which limits the output power of the helix TWT and the miniaturization of the device.Meanwhile,as the operating frequency increases to V-band or above,traditional processing technology cannot meet the accuracy requirements of SWS.Therefore,the design of a new type of SWS based on MEMS that can easy to interact with sheet electron beams has become an important way to develop high-power and miniaturized TWT.Because of this,the research on millimeter-wave helix TWT is carried out.The major work and novelty of this paper are summarized as follows:1.A wide-bar half rectangular-ring helix SWS is proposed to reduce the difficulty of fabrication.Moreover,the wide-bar half rectangular-ring helix SWS,as a new kind of quasi two-dimensional planar structure,features low phase velocity,high coupling impedance,and is more compatible with MEMS.It is suitable for millimeter-wave TWT and easy to miniaturize the device development.2.The effects of the structural parameters on the high-frequency characteristics of the wide-bar half rectangular-ring helix is analyzed.Through optimization analysis,the best structural unit is obtained and the high-frequency characteristics of the equivalent rectangular helix and PH-SEC structure are compared.The results show that the wide-bar half rectangularring helix has a lower normalized phase velocity value and the coupling impedance is significantly improved in the entire operating band.At the same time,a coaxial line coupling device is designed.The electromagnetic simulation software CST is used for simulation verification and the results show that the energy transmission device can provide good transmission performance.3.A W-band sheet beam wide-bar half rectangular-ring helix TWT is designed and the oscillation in the TWT is eliminated by introducing a centralized attenuator.Based on the PIC simulation software,the nonlinear interaction process of the TWT is simulated and analyzed.The PIC simulation results indicate that the maximum output power of the wide-bar half rectangular-ring helix TWT in the 3-d B instantaneous bandwidth is 40.77 W,corresponding to a small signal gain of 26.1 d B.In the range of 65?104GHz,compared with the rectangular helix TWT under the same parameters,the output power of the wide-bar half rectangular-ring helix TWT occupies the advantage,the maximum output power is increased by 43.4%.4.To overcome the disadvantage of the lower coupling impedance of the normal half rectangular-ring helix SWS,a ridge-loaded half rectangular-ring helix SWS is proposed.The simulation results of high-frequency characteristics show that the ridge-loaded half rectangularring helix SWS has a significantly higher coupling impedance compared to the half rectangularring helix SWS while maintaining similar dispersion.The coupling impedance value at the center frequency is increased by 43%.Meanwhile,the research of V-band ridge-loaded half rectangular-ring helix TWT is carried out.The particle simulation results imply that in the range of 52?64 GHz,the ridge-loaded half rectangular-ring helix TWT obtains a peak power of more than 100 W.The peak output power at a typical frequency of 60 GHz is 155 W,corresponding to a gain and electronic efficiency of 31.9 d B and 24%,respectively.Compared with the rectangular helix TWT,the maximum output power has been nearly doubled.