Investigation And Design Of Microwave Reconfigurable Filters

Due to the rapid development of wireless communication technology,the communication systems are increasingly demanded of high performance components.It requires not only possessing the advantages of small size,low cost and high integration level,but also the capability of operating in multi-band or bandwidth control.Hence,reconfigurable technology,as a novel technology,which can satisfy the demand of modern wireless communication technology,receives much attention by national and international scholars.Filter,which is an essential part of the system,also attracts increasing attention,especially for reconfigurable filter.In the reconfigurable mechanism,varactors are widely used because of the advantages of small size,low cost and wide tuning range.The current reconfigurable filter can be generally classified into two catagories: frequency tunable filter and bandwidth tunable filter.For the frequency tunable filter,the bandwidth control(constant bandwidth)during the frequency-tuning process has been widely studied in recent years.However,the frequency-tuning range of filter receives less attention due to the restriction of tunable mechanism and no other factor is introduced about the resonator itself.For the bandwidth tunable filter designs,there are still only two methods,which are changing the coupling between resonators and controlling different frequency modes of multi-mode resonator.The former one will enlarge total insertion loss of the filter and the latter one is too complicated to the development of higher-order filter.Accordingly,a new bandwidth tunable mechanism should be presented for lower insertion loss and easier developing methods.In this paper,a tunable stepped-impedance resonator(SIR),which can be optimized for the frequency-tuning range,is presented.The proposed SIR can optimize the characteristic of itself(e.g.characteristic impedance and electrical length)so that the tunability of frequency can be widened.Two tunable bandpass filters with constant fractional bandwidth and absolute bandwidth are designed and fabricated based on the optimized SIR,respectively.Then,a differential tunable bandstop filter based on the double-sided parallel-strip line(DSPSL)is present.The stopband frequency-range is widened based on the optimized SIR and the common mode response is rejected by the DSPSL.For the bandwidth tunable filter,a novel tunable coupling mechanism based on via-coupling is presented for bandwidth-tuning.This novel tunable coupling mechanism possesses low insertion loss and easy developing method for higher-order design.The designed and fabricated filter based this provides high selectivity,high design flexibility and high fabrication tolerance.The detailed design procedure of the filters is included in this paper.The simulated and measured results all show good agreement,which prove the design methods and the value of practical application.