Study On Synthesis,Simulation And Computer-Aided Tuning Of Microwave Filters

In recent years, the electromagnetic environment has become very complicated andthe frequency spectrum becomes much more crowded. In order to selecting usefulsignals and restrain unwanted signals or noise, microwave filters have become veryimportant and sometimes restrict the development of wireless communication. With thefast development of military wireless communication and commercial mobilecommunication, the filters usually have complicated structures and rigorousperformance. In this case, the traditional filter synthesis theory with Chebyshev functionand structure optimization algorithm can not satisfy the design specifications. So it isneeded to investigate synthesis theory and optimization algorithm of generalizedChebyshev filter with finite transmission zeros. In addition , the CAD simulation andmanual tuning of complicated filters takes a lot of time and energy, which needs asignificant improvement of simulation and tuning efficiency. To solve the previousproblems, this paper has a deeply theoretical and applied research on the aspects such asMicrowave filter synthesis theory, Electromagnetic simulation and optimizationalgorithms and Computer-aided tuning. The primary work is concluded as follows:1. On the filter synthesis theoryThe generalized Chebyshev filters are based on the all-coupled model, The couplingmatrix, which can be physically realized ,should be extracted.Firstly, aim at the situation that the objective functions existed are sensitive to theinitial values, a new objective function is presented. In order to speed up theconvergence of the objective function , we derived formulas for computing its gradientin detail. Numerical simulation results show that the function is not sensitive to theinitial values and takes a short time to converge. To facilitate engineering application,we develop a powerful filter synthesis software, which includes not only the filtersynthesis theory, but also commonly similarity transformation and a variety of topologyoptimization methods.Secondly, the paper proposes a new sort of frequency transformation formulas forasymmetric dual bandpass filter, the transformation formulas can freely introduce thefinite transmission zeros between the first and the second passband to solve theproblems existed in the current asymmetrical frequency transformation that can notflexibly control the bandstop isolation.Finally, diplexer synthesis method with public cavity structure theory is extended to triplexer and multiplexer. Detailed synthesis procedures are presented. The diplexerwith public cavity structure is superior to the diplexer with star-shaped tap traditionalstructure, both in the structural stability and in the ease of tuning. The extention of thetheory makes a better choice in design of the triplexer and multiplexer.2. On electromagnetic simulation and optimization algorithmA new improved aggressive space mapping method is proposed to solve theshortcomings that traditional ASM takes a long time in parameter extraction process andhas inconsistent results. The proposed method uses unified rational function model inparameter extraction process, and the final parameters are obtained from synthesismethod avoiding the drawbacks that parameter fitting process takes a long time andparameters are not inconsistent. Coaxial cavity filter design example has also verifiedthe validity of the algorithm.A systematic study on the commercial simulation software especially onautomated modeling techniques and co-simulation technology. The automatic modelingprogrammes have been developed for the modeling of structures such as H-iris filters,waveguide phased array antenna structures and so on. The general procedures and someimportant parameters settings of the auto-modeling have been summarized.Co-simulation technology between field simulation and schematic simulation has beensuccessfully applied in the design of H-iris filter and a directional coupler. Thesuccessful cases provide a valuable reference to the simulation of more complexstructures and even the system for the future.3. On the computer-aided tuningThe tuning of the filter now is mostly tuned by hand which limits the productivityand raise the cost. It seems like that the development of computer-aided tuning is ashortcut to handle these problems.In this paper, the computer-aided tuning software is developed based on thecombination between automatic measurement technique of a vector network analyzerand zero-pole technique of input reflection coefficient. Tuners successfully tune themechanical tunable filter under the guidance of the software. Currently, there is norelated report to the public for domestic computer-aided tuning software. The successfuldevelopment of the software is also a domestic first try in this field.