Miniature Design And Bending Study Of Hairpin Microstrip Bandpass Filter

Nowadays,the wireless microwave communication technology develops quickly.As a classical frequency selection device,design and the performance of filters directly affect the entire communication system and the RF circuit,therefore the performance and sizing requirements of filters are getting higher.The miniaturization of the filter has become one of the research points to meet the circuit requirements at this stage.Over the past 10 years,flexible materials technology has been developed rapidly,flexible substrates have many advantages,such as superior dielectric properties,the cost is relatively low,so flexible substrates are gradually being widely used in microwave passive devices.The micro-strip device with flexible substrate has good flexibility,thin substrate,easily bending when used,and can be pasted on surface of curved surface to extend the application range of microwave devices.Firstly,this thesis introduces the basic knowledge and preparation theory of the filter,and designs a traditional five-order hairpin bandpass filter with Rogers 4003 substrate based on the electromagnetic theory of the parallel coupled bandpass filter.Then,three four-step hairpin microstrip bandpass filters are designed by using the embedded cross coupling structure,which reduces the size of the whole filter.In order to study the performance of the microwave filter on the flexible substrate,the thesis designs three miniature five-stage hairpin bandpass filters,and compares the three filter to the HFSS simulation under the bending state and the performance of the planar state.It is found that the characteristics of the filter in the band after bending have changed.In order to explore the reasons for the change of performance,this thesis attempts to analyze the coupling coefficients from the angle of the coupled coefficients,that is to analyze the change and regularity of the coupling coefficient after the filter bended.Based on the analysis of the above-mentioned cross coupled structure filter and the filter based on flexible substrate,six filters are processed and measured in this thesis.The S-parameter is tested by the two-port instrument Vector Network Analyzer,and then the results are compared with the software simulation results.