Multi-pass Band Filter Based On Annular Substrate Integrated Waveguide

Substrate Integrated Waveguide(SIW)is a new type of microwave transmission line that uses an array of metallized through-holes to be equivalent to an ideal electric wall,thereby realizing the field transmission mode of a rectangular waveguide.Since the 21 st century,the SIW structure has been widely used in the fields of filters,couplers,antennas and so on.With the flexibility of SIW structure,many different types of filter topologies can be realized.In this thesis,three kinds of multi-pass bandpass filters based on the circular annular SIW or circular annular half-mode substrate integrated waveguide(HMSIW)structure are developed.The main work includes the following aspects:Firstly,the conversion structures of several common microstrip lines and SIW,as well as the width conversion of SIW and rectangular waveguide are introduced.An open-loop SIW structure filter was developed,and the substrate was designed into a circle for its ring structure.The electromagnetic simulation software HFSS was used to analyze and compare the S-parameters of the metallization through-hole at different positions and the ideal electric wall structure,and the appropriate position of the metallization through-hole was selected to replace the ideal electric wall.A triple-band bandpass SIW open-loop filter is designed by using the microstrip line-coplanar waveguide conversion structure.The measured results show that the 3dB passbands are22.12-24.68 GHz,26.48-30.14 GHz,and 32.09-35.89 GHz,respectively.The relative bandwidth was 10.94%,12.93%,and 11.18%,respectively.The minimum insertion loss in the band is 1.6dB,2.26 dB and 3.83 dB,respectively.The return loss in the passband is better than 13.5dB,the three passbands all have out-of-band zero,and the out-of-band suppression is good.Secondly,the odd-even mode analysis was used to analyze the open-circuit stub loaded resonator.Based on the HMSIW structure,an open-circuit stub loaded triple-band bandpass filter was developed,and the ladder-shaped asymptotic conversion structure was adopted.The measured 3dB passbands are 9.12-10.42 GHz,12.46-15.84 GHz,17.32-20.18 GHz,respectively;The relative bandwidth was 13.31%,23.89%,15.25%,respectively.The minimum insertion loss of three 3dB passbands is1.61 dB,1.08 dB and 1.99 dB.The return loss is better than 11 dB.Both sides of the three passbands have out-of-band zeros,and the out-of-band suppression is good.The measured results are in good agreement with the simulation results.Finally,the characteristics of step impedance of microstrip line structure are analyzed,and the common step impedance resonator(SIR)is analyzed.For the circular annular structure,the traditional stepped impedance structure is changed into a fan-shaped stepped impedance loading form,and a stepped impedance dual-band bandpass filter is developed based on SIW structure.In addition,this structure uses microstrip line-coplanar waveguide to achieve impedance matching.The measured results showed that the two 3dB passbands were 20.87-23.62 GHz and 25.47-27.61 GHz,respectively.The relative bandwidth was 12.36% and 8.06%,respectively.The minimum insertion loss is 2.4dB and 3.3dB.The first passband return loss is better than9 dB,and the second passband return loss is better than 11 dB.Both sides of the passband of the filter have out-of-band zeros,and out-of-band suppression is good.