Development Of High Selectivity Crystal Filter

Because of the excellent characteristics, the crystal filter plays a key role in themid-frequency field. However, beacause of the straggling technology and underpinningin our country, the development of high perfomance crystal filter in our country stilldrop behind the developed country. In order to meet the high-demand of modernweapon equipment, the research of high performance crystal filter is very necessary atpresent.This thesis was based on the project of “The discrete quartz crystal filter” whichsubmitted by a national department. This project was aim to resolve the key technologyproblem of crystal filter and improve the producing ability of crystal filter. Thisdissertation mainly studies on the high-selective crystal filter. The key technology ofcrystal filter which nice shape factor, high stopband attenuation and high temperaturestability were studied theoretically and experimentally. The main research work andresults were as following:1. Briefly discussed the most common theories and methods of crystal filter. Thebrigde narrowband eight-crystal filter circuit was designed in detail based on thenetwork synthesis. Besides, the circuit was improved based on our years of designexperience. And the computer stimulation results showed that the novel circuit wasfeasible.2. Detailedly introduced the development process of the high-selective crystalfilter. Moreover, critical process points in the crystal and filter production process werediscussed respectively. Factors which affected the key parameters of crystal filter weresummarized, and related solutions were proposed to resolve the technical problems ofhigh stopband attenuation and wide temperature stability of crystal filter.3. Comparison between the measured results of samples and technical agreementwas given in this thesis. Besides, the research results and application of this projectwere introduced briefly. The results showed that the high-selective crystal filterachieved requirements of the technical agreement and the research results weresuccessfully promoted in application. Through the great work of this thesis, high performance crystal filter wasachieved. It’s shape factor (K60/3) is less than2, stopband attenuation is greater than90dB, and application range is-55℃~+85℃.