Fast electromagnetic analysis and design of multiple coupled cavity structures.

摘要

With continuous development of global, mobile, and cellular communications, tremendous efforts on the miniaturization of microwave filters have been made in recent years. Rapid development of the technology poses extraordinary demands on high performance and low cost microwave filters and multiplexers. Accurate design of high performance filters and multiplexers relies on rigorous electromagnetic simulations of the resonant, coupling, and interconnecting structures involved. This dissertation is devoted to fast electromagnetic analysis and modeling of variety of conductor-loaded cavity resonators and related coupling and tuning structures widely used in multiple coupled cavity filters and multiplexers.; In this dissertation a modular numerical method based on surface integral equation with moment method solution (SIE-MoM) is proposed for the analysis of electromagnetic fields and determination of circuit parameters of a coupled cavity structure. Computational speed of the method is greatly enhanced by introduction of a novel approach for rapid calculation of the potential Green's functions in a rectangular box which employs a three-dimensional Chebyshev polynomial approximation for rapid evaluation of the eight components of potential Green's functions simultaneously.; The proposed methodology is used for fast full-wave analysis of a variety of rectangular cavities loaded with perfectly conducting objects of arbitrary shape and orientation. Resonant frequencies and modal field distributions of different single and dual-mode resonators are calculated and the results are compared to those obtained from a commercial EM simulator and published experimental data with excellent agreement. A general formulation for rigorous modeling of coaxial probes in conductor-loaded cavities based on SIE-MoM technique is also introduced and the frequency responses of single and dual-mode filters made of conducting disks inside a rectangular enclosure are calculated. The effects of coupling and tuning screws in dual-mode resonators are also investigated.; In a multiple coupled cavity structure, each resonator is modeled by a generalized admittance matrix (GAM) obtained from the SIE-MoM technique. A cascading procedure is then applied to successively combine the GAM of adjacent resonators and to obtain the admittance matrix of the entire structure. Coupling irises of any shape or orientation can be simulated accurately. To further enhance the computational speed of this model, a specialized interpolation scheme is introduced for fast evaluation of the GAM over a wide frequency band. The proposed methodology is used to compute the coupling coefficient between two slot-coupled conductor-loaded cavities which are not necessarily identical by finding the natural frequencies of the structure. Both conducting disks and slot-coupled combline resonators are simulated and the results are shown to be in excellent agreement with those obtained from a commercial EM simulator and measurements.; It is demonstrated that versatility and accuracy of the SIE-MoM technique combined with a fast Green's function can provide an efficient electromagnetic design and optimization environment for highly demanded multiple coupled cavity structures. Variety of mechanical features or electrical components in these structures whose fast full-wave modeling is not possible by mode matching method or is very time consuming by FEM or FDTD method can now be treated with a rather short CPU time.