Research On The Miniaturized Multiband Bandpass Filters

As the great advance of communication technology,wireless system needs to be diversiform,compatible with multi-standard,integrated multi-services which gets the focus of attention gradually.While multi-passband filter is the crucial component,this thesis proposed several multiband works based on advanced design method as following:With multi-path interaction principle,this thesis combines different signal path,coupling mechanism and coupling scheme to present multiband filter using microstrip and waveguide structure.On the one hand,by nested loading spiral coupled line on the split meander loop,inductive effect is enhanced and a miniaturized strip dual band filter can be presented.Its 3-dB fractional bandwidth are 42.8%and 20.8%,with a overall dimension equal 0.023_g~2?,where_g?is the wavelength at central frequency of the first passband.Then,to avoid dimension increase,inherent propagation instant difference between parallel-plate waveguide and fin line is utilized.In this way,E plane septa is split and multi-path inference and tri-or quad-passband waveguide filters are achieved.Therefore,multi-path interaction mechanism has been a good candidate for compact microstrip or waveguide multi-passband filter circuits.Since existing loop model is sameness,the proposed abnormal shape loop resonator with split modes and descendant resonant frequency is proposed.Therefore,compact microstrip multiband frequency response can be designed more flexible.Firstly,by attaching stepped impedance resonator(SIR)to specially cascading SIRs loop,multimode and sext-passband work is realized,with its physical size equal 0.029?_g~2.In addition,for universal case of cascading SIRs,inner circle outer polygon loop model is shown.Using m?bius transformation,eigen function expansion,equivalent circuits or taper line fitting techniques,respectively,its characteristics like resonant modes and frequencies are investigated.With several capacitive or inductive stubs loaded on the inner circle outer polygon abnormal loop,some multiband filters with compactness are designed.At the same time,triangle,square,pentagon and hexagon are implemented in abnormal loop to present quad-/quint/sext-band filters,where their maximum and minimum sizes reach 0.067 and 0.019?_g~2.Accordingly,on a basis of this two kinds of abnormal resonant loop,various miniaturized multiband filters can be proposed.