Design Of Balanced Bandpass Filters Based On Ring And Slotline Resonators

With the progress of communication technologies,especially the gradually maturation and commercially available of 5G,broadband and multi-band technology has become a research hotspot.Under this research background,split ring resonator(SRR),stepped impedance resonator(SIR)and slotline resonator are studied to achieve high stability,low power consumption,high noise suppression and good filtering characteristics of designed filter.Two balanced wideband bandpass filters(BPFs)and a balanced tri-band BPF are designed.The main contents of this thesis mainly include the following aspects:1.A balanced wideband BPF with high selectivity is introduced based on the basic theory of ring resonator.Two transmission zeros(TZs)are introduced on both side of different mode(DM)passband by parallel coupled microstrip line and microstrip-slotline conversion.High selectivity,controllable bandwidth are realized.Subsequently,a balanced wideband BPF is designed based on the basic theory of slotline resonator.It is fed by modified balanced feeding structure.Multi-Transmission Poles(TPs)are introduced for multi-mode characteristic of coupling parallel microstrip line and slotline resonator.In-band flatness is improved by introducing interdigital coupling structure.Two TZs are introduced to improved out-band selectivity.Low insert loss,high common mode(CM)rejection and good wideband characteristic have been achieved.2.A balanced wideband BPF is designed based on the second kind of modified balanced feeding structure.Four TPs are introduced by step impedance slotline resonator and open stub.Lumped capacitances are loaded to improve the DM frequency response.TZ can be adjusted by changing the capacity value to improve the out-band selectivity.Wideband,high CM rejection and adjustable frequency response have been achieved.3.A balanced tri-band BPF is designed based on the basic theory of stepped impedance ring resonator.Two TPs are introduced between passbands by SIR.The third passband is introduced by adding uniform impedance resonator outside the SRR.Independently controllable passband is achieved for the independence between the resonators.Three TZs are introduced by multi-path structure to improve the out-band selectivity.