Study Of Fast Finite-element Theory And CAD Technique For High-frequency Circuits In Microwave Tubes

Microwave tubes are widely applied as the core electron devices in many militaryfields such as the multifunction radar, the electronic countermeasures equipment, thespace communication and so on. The high-frequency circuit (HFC) is one of the mostimportant parts in the microwave tubes, where the electron beam and theelectromagnetic wave interacts each other. The performance of the HFC in themicrowave tube directly affect the bandwidth, gain, output power, efficiency and anyother performance parameter of the microwave tubes. As the requirement of theperformance of the microwave tubes improves, the efficiency and performance of theHFC are also required to be improved. However, the design of high-efficient andhigh-performance HFC eagerly demands more accurate, more efficient and more robustthree dimensional numerical algorithm and CAD software for HFC.The research works of this dissertation are focused on the fast finite-element theoryand CAD technique for the HFC in the microwave tubes. Several important andvaluable results are listed as below:1. We propose a fast finite-element method (FEM) for the arbitrary HFC in themicrowave tube. This advanced method mainly contains four new techniques:(1) Anovel rotated periodic boundary condition which utilize the longitudinal and azimuthalperiodicity of the HFC is proposed to significantly improve the efficiency of simulatingthe HFC using the FEM.(2) By using the implicit restarted Arnoldi method based onshift-invert preconditioner and the fast multi-front LU factorization, an improvedmodified implicit restarted Arnoldi method is proposed to efficiently solve the finallarge generalized eigenvalue problem.(3) Both the lower and higher order tetrahedralbasis functions are applied in the finite-element analysis.(4) The post-processingparameters of the HFC can precisely be computed with the tangential-vector FEM.2. We investigate many key techniques in the fast finite-element analysis of theHFC using a new second-order hierarchical basis.(1) A convenient and efficientapproach for removing the spurious dc modes in finite-element solutions for modelingmicrowave tubes is proposed.(2) By utilize the hierarchical property of the basis, an advanced p-type multigrid eigensolver is proposed and applied to quite efficiently solvethe finial large eigenvalue problem.3. We make deeply investigation on the fast finite-element analysis of the lossyHFC in the microwave tubes.(1) A novel a new frequency-specified eigenmodeanalysis for SWSs is proposed and utilized.(2) To further significantly improve theefficiency of modeling lossy HFC, an improved inexact implicit restarted Arnoldimethod is proposed.4. A novel three-dimensional finite-element modeling technique for arbitrary lossyHFCs of microwave tubes without matching meshes is presented. By employing thistechnique, the cold parameters of HFCs can be accurately and quickly obtained from theeigenmode analysis for SWSs with completely nonmatching meshes. Moreover, a newsecond order TE periodic boundary condition is proposed to improve the modelingefficiency of lossy HFCs with nonmatching meshes and this technique is very suitablefor application of the rotated periodic boundary condition.5. Based on the fast finite-element theory, we developed an advancedthree-dimensional finite-element electromagnetic-simulation tool for the HFCs in themicrowave tubes－High Frequency Circuit Simulator (HFCS). The HFCS have auser-friendly interface module, a fast model constructor for the HFC, a high qualitymesh generator, accurate and fast finite-element analysis and eiegensolver modules, andaccurate and rich post-processing functions. The HFCS is more efficient than the twocommercial software CST MWS and HFSS in the eigenmode analysis of the HFCs inthe microwave tubes. The HFCS has been released in many institutes and factory forresearching and designing the microwave tubes. The HFCS has been benefitted theresearch and manufacture of microwave tubes in China.