Research And Design Of Reconfigurable Filter

In recent years,by the rapid development of communication technology,lots of the communication applications in several network protocol come out.Reconfigurable filter,as an important part of the reconfigurable RF front-end,need to ensure the filter's passband selectivity at the same time to satisfy all kinds of reconfigurable function.Fast tuning speed,more tuning modes,small volume,high integration,low cost and high reliability become research hot spot.Varactors and PIN diodes as the reconfigurable components applied in this paper,by studying the way of loading and reconfigurable thoery,there is reconfigurable components on the end of the transmission line and between the resonator units.Three reconfigurable filters of different functions finally worked out,based on the odd-even mode method and electromagnetic simulation software to calculate and verify:1.Based on odd-even mode analysis of the E shape dual-mode resonator,the double passband frequency reconfigurable bandpass filter is established by using the varactor at branch knot.The even mode's resonant frequency can be influenced by varactor,so the wide range change of the second passband frequency is realized by changing the way of feeding and choosing appropriate varactor.Single-double passband switched when the frequency of the two passband coincide,and ensure the two passband bandwidth keeping unchanged.2.After the in-depth study of muti-mode resonator,a wideband bandpass filter has been desighed by loading an open-stub branch knot on E shape dual-mode resonator to form a three-mode resonator,which has flattered group delay and good selectivity.Analysing this three-mode resonant's characteristics and mastered the changing rule of three poles,the open-stub at top and bottom control the change of high and low frequency poles,the microstrip line controls the change of the middle pole.So,joining the varactor at the end of the microstrip line and open-stubs,a reconfigurable filter is designed which absolute bandwidth is changed and center frequency is unchanged.3.Through designing on the two reconfigurable filter,a three-section SIR bandpass filter is achieved by the mutual coupling structure on varactor,it's center frequency and bandwidth are independently reconfigurable.Using PIN diodes as RF switch,choose one out of four pathways to finish the reconfigurable center frequency.In one pathband,adjustment on the varactor used to connect coupling resonator unit and change coupling coefficient to finish the reconfigurable bandwidth.All three filters had gone through analysis,discussion and validation,finally achieved wide tuning range and easy to control,at the same time realized the miniaturization and high stability.