Development Of High Frequency Narrow-band And Small Group Delay Crystal Filter

Crystal filter is widely used in modern communication systems. With the rapiddevelopment of communication technology, the requirements for crystal filter are alsoincreasing in the communication system. High selectivity in the amplitude versusfrequency and small group delay in the phase versus frequency are required for crystalfilter. As a key device in the communication system, the crystal filter’s amplitude offrequency characteristic and phase versus frequency characteristics will directlydetermine the performance of the communication system. Besides, when the filter isworking in a wide temperature range environments, it is also necessary to meet thetechnical requirements of the communication system.In this context, in order to meet the requirements of the communication system forthe amplitude versus frequency characteristic and phase versus frequencycharacteristics, a detailed study on crystal filter design method and developmentprocess was carried out in this thesis. Based on the crystal filter theory, the researchspecial how to reconcile the contradictions of amplitude versus frequency and phaseversus frequency characteristics in crystal filter was discussed. Measures to improvethe temperature stability of the crystal filter are proposed by the research on the factorsaffecting the temperature stability of the crystal filter. The main content of the papersare below:(1) The study on the crystal filter circuit and working principle, especially theintegrated design method process.(2) Based on the study on the response function of the filter, a design methodwhich combined advantage of chebyshev functions and bessel functions are proposed.This method effectively reconciled the contradictions of amplitude versus frequencyand phase versus frequency characteristics.(3) Crystal filter design method is proposed to take the combination of theoreticaldesign and simulation optimization. This purposeful method effectively reduced therepeated nature of the development process and improved the development efficiency. (4) Solutions to improve the performance of crystal filter are proposed by theresearch on how to reconcile the contradictions of amplitude versus frequency andphase versus frequency characteristics.(5) Solutions to improve the temperature stability are proposed by the research onthe factors affecting the temperature stability of the crystal filter.