Research On The Beam-Wave Interaction Theory Of Folded Waveguide TWTs

Traveling wave tubes(TWTs) are the most widely-used microwave vacuum electrionic devices(VEDs), for their advantages of high gain, broad bandwidth and low noise and so on. As the frequency of VEDs extends to millimeter wave regime, higher power and wider band-width are required in the applications of radar, communications, electronic counter measures and imaging, which brings new challenge to the development of VEDs. For VEDs, higher frequency means smaller dimensions of the interaction circuits. Common helix TWTs are lack of power capacity and heat dissipation potential. As to conventional coupled-cavity(CC) TWTs, the band width is rather narrow in spite of high output power. Because of both the characteristics of large power capacity as CC-TWTs and wide band as helix-TWTs they have, folded waveguide(FWG) TWTs can be used as millimeter-wave amplifiers with high frequency, high power and wide band-width. So, they have gradually drawn much attention from researchers.Depending on traditional experimental method to improve the performance of TWTs cause not only low efficiency but also large expense of money and time. Accordingly, accurate simulation softwares for the beam and wave interaction(BWI) of TWTs are of great significance for the improvement of their performances. So theories for simulating BWI of these TWTs and the corresponding simulation softwares are essentially important for the developments of TWTs, including FWG-TWTs. In this doctoral dissertation, the work is mainly focused on the generalized theory model suitable for the BWI of TWTs and FWG-TWTs-specific frequency-dependent theory model. The main work and innovations of this dissertation are as below.1. A generalized simulation technique has been developed for simulating BWI in various types of TWTs. Firstly, the digitized radio frequency(RF) fields are assumed to be constant during the process of BWI. The generalized RF field equations are derived from Maxwell equations. The digitized RF fields are obtained from high frequency electromagnetic simulation software, which make it possible to simulate BWI for some slow-wave circuits that have difficulty in obtaining analytical RF fields. The space charge(SC) fields are solved by quasi particle-in-cell(PIC) method, on combining the RF field equations and the dynamic electron equations, the generalized frequency-dependent simulation technique for various types of TWTs is developed. A three-dimensional code is implemented based on the generalized theory model and applied in the nonlinear simulations for three common slow-wave structure TWTs. Simulation results prove the validation of this generalized simulation technique.2. A three-port network model for FWG slow-wave structure(SWS) is developed. The unit cell in the periodic circuits is represented by a three-port network, and the relationship between voltages and currents is established by circuit features. Values of the impedance elements that characterize the model are determined by characteristic parameters of RF structures. Once the impedance elements are determined, the relationship between voltages and currents for the unit cell is established. According to the transmission characteristic of TWT SWS, the coupled relations between voltages and currents of adjacent unit cells are determined, as a result, the cascaded matrix is established. In addition, RF characteristics of FWG SWSs are studied with analytical methods and verified by results from finite-element electromagnetic code.3. To solve the problem that no suitable equivalent attenuation model for the three-port network model, a new attenuation model based on the the three-port network is presented. The equivalent circuit model is with simple structure and the features of ports are consistent with those of three-port network. Several additional resistors are in series with the impedances. And the values of the resistors can be properly chosen using an iteration procedure.4. Based on the three-port network model, the one-dimensional(1-D) and three-dimensional(3-D) BWI frequency-domain theories for FWG TWTs are developed. The 1-D and 3-D simulation codes for simulating the BWI are implemented and used to simulate a practical FWG TWT. The validation of the nonlinear theory model for FWG TWTs are presented with the consistency between the simulation and experimental results.5. A CAD software of BWI for FWG TWTs named BWIS-FW is implemented base on the BWI nonlinear theory model of FWG TWTs. The software can be applied in the optimization of BWI parameters of TWTs, with convenient and visualized operation. Both 1-D and 3-D modules are included in the code, and tight relations with High Frequency Circuit Simulator(HFCS), which is benefit for the design and optimization of FWG TWTs.