Theoretical Modeling And Efficient Algorithm For Electromagnetic Transmission And Radiation Of Beam Waveguide

The accurate modeling and efficient solving of the beam waveguide(BWG)transmission system is always a challenge in the computational electromagnetics. Thebeam waveguide always has large size compared with the wavelength, complexstructure, and composite metallic-material structure. It cause the huge computation loadand the slow iteration process. In this thesis, the integral equation(IE) method and themode matching(MM) method are combined together to simplify the model, and thepreconditioning technique is used to accelerate the convergence speed. To deal with thestructure of electrically large size, the multilevel fast multipole algorithm(MLFMA) isused. Decomposing the free space Green’s function by the style of aggregation,transformation and disaggregation, MLFMA successfully reduces the computationcomplexity to O (N log N). The transmission problems of beam waveguide withelectronically large size and complex structure can be solved efficiently by using thisintegrated modelling and simulation environment. The characteristics of reflectors withany number, arbitrary shape, and arbitrary position while illuminated by the horn feedcan be solved efficiently. In practical application, the method mentioned above can beused to obtain the radiation and scattering characteristics of the radomes, the frequencyselective surfaces, and the large side-fed reflector antennas efficiently.First, the traditional numerical methods of solving the excitation, transmission andradiation problems of the complex structure are introduced. Including the analyticalmethod, the high-frequency method, the differential equation method, the integralequation method and the hybrid method. The basis functions and the method of momentare deeply studyed. Finally, the integral equation method is combined with the modematching method and the equivalent model of the waveguide-fed cavities.By studying the equivalent model of the waveguide, we got the efficient numericalmethod of solving the excitation, transmission and radiation problems of theelectrically-large and complex beam waveguide structures. We have discussed theaccurate modeling and effective numerical solving of the transmission and radiation ofthe waveguide-fed electrically-large structure problems(including the conductor or thecomposite metallic-material beam waveguide and the arbitrary multi-port radiation structures). Then the MLFMA is used to improve the efficiency of the solving process.Using the integral equation method, we only need to discrete the surface of the ideaconductor and the volume of the dielectric area. The characteristic of the beamwaveguide always contains large space without any PEC or volumn structure. Then thenumber of unknowns is much less and the solving efficiency is much higher comparedby using the differential equation methods. Using the mode matching method, andconsidering the reflecting guide wave modes, we can get the matching situation on theexciting erea and the accurate results.The method of dealing with the single waveguide-fed problem is expanded tosimulate the multi-port waveguide-fed antenna array problems. The increasing numberof antenna elements brings the large electrical size. And there are always the elementswith different structure and feeding mode and the complex electromagnetic coupling.The requirement of computing resource is great, which even cannot be supplied. Themodel and efficient algorithm raised in this thesis can deal with the multi-portwaveguide-fed transmission and radiation problems with feeds of arbitrary amount,structure, excitation mode and relative position.In order to further improve the efficient of solving the transmission problems of thebeam waveguide with electrically large size structure, we used the phase-extracted(PE)basis functions to describe the surface electric current. The reason is that the phase ofthe electric induced current on the PEC surface of the beam waveguide changeperiodically along the direction of the incident wave. Comparing with the traditionalbasis functions, the PE basis function can be defined on the larger patches. Using thisbasis function, the unknowns is directly reduced and the ability of solving the beamwaveguide with electronically large size is greatly improved.In the solving process, the preconditioning technique is used, and the better effectis got. Moreover, the OpenMP parallel technique is adopted and the solving efficiency isgreatly improved. The author has been developed the program codes based on themethods mentioned in this dissertation, which is validated by the numerical experiment.