Design And Research Of Microstrip Electronically Tunable Bandpass Filter

With the rapid development of information society technology in recent years,mobile wireless communication has been closely linked with people's life and work.In order to resolve the shortage of the spectrum,as the same to improve the spectrum utilization,using cognitive radio approach to dynamic spectrum allocation has become a hot topic in the industry.As one of the realization of essential way,the multi-band and multi-mode device,which can meet the communication of different spectrum and the different communication standard,can fit the requirement of the communication by the coverage of the multi-band.The multi-band tunable filter,as an important part of function module in the multi-mode device,plays an important role in cognitive radio.Tunable filter not only reduces the volume of the system,but also reduces the power consumption,comparing with the traditional filter.In addition,tunable filter has been an important application in spread spectrum and FM radio communication.Thus tunable filter has important research value.Tunable filter designed,which based on discrete PIN diode switches and which based on continuous varactor diode,have been a research in this paper.Firstly,review the design method of the filter,frequency conversion,conversion and other parameters necessary technical means.Then regarding implementations of the discrete and continuous adjustable filter were analyzed and compared,at the same time,designed the discrete tunable filter based on PIN diodes and applied varactor to achieve continuous tunable filter are presented.Next,based on the characteristic of the SIR basic structural and the resonance condition,a dual-mode resonator SIR E-type structure is proposed.From the odd-even mode resonant circuit equivalent of view,analysis of the dual resonance characteristics SIR E-type structure with a weak coupling,and then designing a dual-band band-pass filter.Through loading tuning element PIN diode switch on the basis of the previous,using PIN diode connected and disconnected different characteristics,the number of resonant mode is changed and finally a single dual-band discrete tunable filter is designed successfully.Finally,through analyzing the character of the open stubs loaded symmetrically coupled resonator and equivalent circuit,in the symmetrical position of the coupled half-wave resonator shunt connected varactors and a tunable filter is designed by changing the electricallength of the resonator effectively,it's center frequency can continuously adjust from1.06 GHz to 1.33 GHz.Based on the single frequency tunable filter,using the odd-even mode theory to analysis it,Using a secondary harmonic forming a second pass-band by loading adjustable element at the center of two coupled resonators,then a tunable dual-band band-pass filter is designed finally and it can maintain good pass-band performance in whole adjustment process.Furthermore,keeping the DC bias voltage V1 constant and varying only V2,the first pass-band center frequency is fixed,and the second pass-band frequency is adjustable.Finally,the tunable filter is fabricated and measured,then the effectiveness of the design method is verified.