| The next generation radar, communications and electronic warfare presents a new challenge to the performance of microwave power devices, such as high peak power, high average power, ultra broad band, low noise, the match of gain and phase, etc. Meanwhile, the advanced airborne and space weapon systems put forward higher demand for the size, weight, efficiency, life-span and reliability of the devices. On the background of the urgent need, the microwave power module (MPM) began to appear in the nineties of the twentieth century. Through the past of more than ten years, MPM has maturated overseas and been largely used in radar, electronic countermeasure, decoy, phased array, space communications and so on.MPM is called a super-component and consists of integral power conditioner, solid-state amplifier and mini traveling-wave tube (TWT). Mini TWT is the core part at the end of MPM, and its performance can directly determine the whole module's performance. So, the design and fabrication of mini TWT is the first step of MPM development. Except for being integrated into MPM, mini TWT also can be separately used in radar, electronic countermeasure and space communications to minimize the equipments. Besides small size, mini TWT also is characteristic of low working voltage, high efficiency and ultra broad band. The traditional experience and theory analysis is almost invalid, and more modern CAD technology must be used to design and investigate mini TWT.In this dissertation, each of mini helical TWT building components is theory analyzed and CAD investigated. On the basis of theory analysis and CAD investigation, several mini helical TWTs used in MPM have been fabricated and measured. In this doctor dissertation, the main achievements include several aspects as the followings:(1) The 2～6GHz mini TWT used in MPM is designed and fabricated. The measurement output power is over 50W at the end of the band and 100W in the middle of the band. The whole size of the mini TWT is smaller than 260mm×30mm×25mm .(2) The high frequency characteristics of mini TWT are investigated in detail.On the basis of helix sheath model and vane finite thickness model, the high frequency characteristics of ridge-loaded helical slow-wave structure (SWS) are analyzed with field match method. The paper presents the sector equivalent method for loaded ridge and support rod, so the process of solution is simplified. With this method, the dispersion characteristics, interaction impedance and attenuation are derived for ridge-loaded helical SWS.To simulate the high frequency characteristics of helical SWS, the macro program is completed based on 3-Dimensional (3-D) simulation codes, including Ansoft HFSS, CST Microwave Studio and CST Mafia. Compared with the past graphic-user-interface (GUI) method, the macro-program method is more efficient and brief for the designer.With the accurate 3-D simulation model, several prominent approximations are analyzed quantitatively for the traditional perturbation measurement of SWS interaction impedance. The definition method with 3-D simulation is presented to obtain interaction impedance of SWS with lower cost and higher accuracy.With the simulation model, the influence of slow-wave circuit manufacture tolerance on high frequency characteristics and output power is analytically evaluated for 2～6GHz mini TWT. Some useful conclusions are obtained and supply manufactures with practical references in controlling process parameters with less cost.(3) The beam-wave interaction of mini TWT is investigated in detail.The nonlinear theory analysis of beam-wave interaction is studied. Considering the higher harmonics, the TWT nonlinear working equations of P. K. Tien are newly derived. Considering the current and field variations on the cross-section of electron beam, the space charge field equations of L. A. Vainstein are newly derived.With the 1-D and 2-D nonlinear code, the beam-wave interaction is calculated, and two sets of manufacture schemes are designed out for 2～6GHz mini TWT. The influence of direct-current working point, sever and attenuator on beam-wave interaction is analyzed.Based on electromagnetic (EM) particle-in-cell (PIC) simulation software MAGIC, the 2.5-D PIC simulation code is completed to investigate the nonlinear beam-wave interaction process of a helical TWT. The tube length, electron beam current, voltage and focus magnetic field is optimized, and the optimum working conditions are obtained.2.5-D PIC code MAGIC and 3-D EM code HFSS is used to investigate the helix TWT for electronic efficiency enhancement. A positively-negatively tapered helix TWT has been designed and fabricated. The result shows the measurement efficiency of the tapered TWT improves 10% on the non-tapered one in the 8～11 GHz band.The dispersion shaping and harmonic suppression is theory analyzed and simulation investigated. The negative dispersion is formed to suppress the harmonic content by over loaded SWS. For the 2～6 GHz mini TWT, the second harmonic level is lower 6 dB than before at the low frequency end of the band.(4) The couple connector of mini TWT is studied.For match with the couple connector, the characteristic impedance of helical SWS must be known firstly. The concept of effective network method is presented in this paper. On the basis of that, the characteristic impedance expression of ridge-loaded helical SWS is derived.From network connective matrix, the scatter (S) parameter of a single couple connector is derived from the whole S parameter of the helical SWS joined with two couple connectors.At last, the transform from one coaxial line to another is calculated and optimized. The coaxial transform connector is designed and fabricated with less size.(5) The electron optics system is designed. With the 2-D nonlinear code, the electron gun, periodic permanent magnet (PPM) stack and multistage depressed collector is designed.(6) Cold-test and hot-test experiment of TWT is studied. We choose the traveling-wave method for dispersion test and nonresonant perturbation method for interaction impedance test. Based on this, the cold-test system of TWTs is constructed up. With the system, the cold-test of two SWS samples is done. Several 2～6GHz mini TWTs used in MPM is assembled, and the hot-test experiment is done. The 8～11 GHz TWT for electronic efficiency enhancement is assembled, and the hot-test experiment is done too.
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