Research And Design Of Stripline Filter

Microwave filter is one of the important passive components in modern WirelessCommunication System. As Microwave Communication System performancerequirements get higher and higher, filters are also designed towards high performance，light-weight and miniaturization. Compared with waveguide and coaxial, strip-linefilters have many advantages such as superior performance，small volume, light weight,low cost and so on，and the strip-line components are easy to integrated with otheractive circuits. Because of this, using strip-line as wave-guided structure, based onChebyshev low-pass prototype filter, combined with modern filter design methods,low-pass filter and high-pass filter with high performance and miniaturization aredeveloped in this thesis. The researches of this thesis are listed as follow:First, this thesis presents the classification and main technical parameters of filters,and emphatically introduces the basic type of low-pass prototype filter and the responsecharacteristics. According to the response characteristics, this thesis choose Chebyshevlow-pass prototype filter. Frequency conversion and impedance transition that arenecessary for calculating formulas for insertion loss method are introduced. This thesisalso presents geometry of strip-line, transmission characteristics, power capacity and thesize to choose. All of these lay the theoretical foundation for strip-line filter design.Secondly, the equivalent relation of transmission line and lumped components isanalyzed. The formulas of calculating stepped impedance line are also present in thisthesis. Based on the traditional design method of stepped impedance line low-pass filter,this thesis presents a new type of low-pass filter with coupling capacitance, and thecircuit analysis, electromagnetic simulation and machining test are finished. Resultsshow that this new type of low-pass filter has a cutoff frequency transition steep,compact structure, small size, wide range of stop-band characteristics compared withthe traditional stepped impedance line low-pass filter.Finally, this thesis introduces an optimum distribution parameters high-pass filterprototype, and based on the optimum distributed high-pass filter prototype, a high-passfilter employing shorted stubs is designed. The relation between the bandwidth and impedance of shorted stub is analyzed, and the formula that is used to calculate lengthof shorted stubs based on cutoff frequency is determined. Electromagnetic simulationand machining test of high-pass filter are finished. Actual test results and simulationresults are basically identical.In the end of this thesis the difficulties encountered in design of strip-line filter andthe next research is prospected. All of these works lay the foundation of furtherresearch in the future.