Design And Implementation Of Microstrip Bandstop Filters

Microstrip bandstop filter can effectively eliminate the interference in the signal,so it is widely used in testing,wireless communication and other communication systems.With the development of the communication system,different applications have different requirements of the microstrip bandstop filter,such as low passband loss,high stopband rejection,narrow transition band,and compact structures.Therefore,the required performance of the bandstop filter are different in different application scenarios and different communication systems.Many different types of bandstop filters such as absorptive bandstop filter,wide stopband bandstop filter and multiband bandstop filter have been introduced.The basic principle,circuit structure and design steps of various microstrip bandstop filters are analyzed in this thesis.Due to different requirements of bandstop filter,this thesis design a coupled-line microstrip bandstop filter with absorptive stopband,a wideband microstrip bandstop filter using stepped-impedance coupled line,a quad-band microstrip bandstop filter using dual-mode open loop resonators and a dual-band microstrip bandstop filter with multiple transmission poles.Firstly,the basic design principle of bandstop filter is introduced.From the low pass prototype circuit as the starting point,and then the band stop filter is designed by frequency conversion.Secondly,this thesis design a coupled-line microstrip bandstop filter with absorptive stopband.A wideband microstrip bandstop filter using stepped-impedance coupled line,a based on dual-mode open loop resonators quad-band microstrip BSF and a dual-band microstrip bandstop filter with multiple transmission poles and introduce their design methods and design steps in detail.Lastly,a coupled-line microstrip bandstop filter with absorptive stopband and a dual-band microstrip bandstop filter with multiple transmission poles are fabricated and the measured results are in good agreement with simulation results.The filter achieves good performance.