Design And Investigations Of Microstrip Filters

Microwave filter is the most important frequency selection components of communication system.With the development of microwave technology,microwave theory and microwave technology are becoming more and more abundant,the structure of microwave system is more and more complex,and the requirements for microwave filter are also more and more strict.Miniaturized and high performance filters have attracted much attention from researchers.Based on the background mentioned,the filters with miniaturized and high performance have caught greater attention from the resonator,dielectric material,transmission zeros and double bandpass.The development of microwave materials has promoted the miniaturization of microstrip filter.In this paper,MgTiO₃ based microwave dielectric ceramic were doped for a better microwave properties,phase constitution?microstructure and microwave properties were investigated systematically.In order to select proper microwave ceramic material for filter substrate,experiments of modifying MgTiO₃ microwave dielectric performance are put forward.The main work can be summarized as:Firstly,a novel gap-capacitance loading dual-mode filter based on capacitance loading and dual-mode T-shaped resonator is designed.Measurement results prove that such a filter based on gap-capacitance loading is small in size.The even-mode and odd-mode resonance frequency of dual-mode T-shaped resonator was studied and its application in filter bandwidth design.In comparison with FR4??r = 4.5?and 0.93Mg0.97Zn0.035TiO3.005-0.07CaTiO3??r=21.01?ceramics,the filter using the proposed ceramics not only shows a tremendous reduction in the insertion loss but also demonstrates a cut?about 80%?in its efficacious dimensions.Secondly,transmission zeros play an important part in requirements of better rejection and they can improve the frequency selectivity and provide better characteristics of the stopband.At present,researches on introducing transmission zeros are mainly developed from cross-coupling,mixed electric and magnetic coupling and source-load coupling.A compact filter with six transmission zeros based on cross-coupling and mixed electric and magnetic coupling is proposed to implement quasi-ellitiptic filtering responses.A three cavity square split ring filter and two cavity hexagon split ring filter with source-load coupling are designed.A three cavity open-loop filter is designed to produce a transmission zero by combining the cross coupling and the source load coupling.The dual band-pass filter applied to WLAN is realized by embedding the smaller size SIR which control the high frequency of filter into the bigger size SIR which control the low frequency of filter.The tri-band filter is studies based on parallel SIR structure.Finally,the thesis introduces the fabrication,phase constitution and microwave properties of MgTiO₃ based microwave dielectric ceramic.From the perspective of ?r,Q×f,?f,a dielectric constant??r?of 21.01,a Q×f value of 80,912?at 7.94GHz?and at f value of 0.76×10^-6/°C which satisfied filter substrates were obtained for 0.93Mg_0.97Zn_0.035TiO_3.005-0.07CaTiO₃ ceramics sintered at 1250°C for 4h.