Design And Implementation Of High Selectivity Bandpass Filter Based On SIW Technology

As an indispensable component of the front end circuit of the communication system,the performance of the filter will directly affect the reception,emission and transmission of the signal.With the continuous development and improvement of the whole communication system,the requirements for each component are constantly improving,and the filter is also developing towards the direction of miniaturization and high performance.In the process of decades of research,Substrate Integrated Waveguide(SIW)has attracted the attention of filter designers because of its unique structure and electromagnetic characteristics.The structure of SIW is not only light,small,easy to be machined and easy to be integrated with the planar circuit,but also with small radiation loss and high power capacity like the traditional waveguide.These characteristics make it a design platform to adapt to the development of miniaturized high-performance filters design.When it comes to the high performance of the filter,the high selectivity of the filter has to be mentioned.The high selectivity filter can be used to filter the unnecessary interference signal more effectively,which can greatly improve the transmission efficiency of the useful signal.However,the most common way to improve the selectivity of the filter is to introduce the Transition Zeros(TZs).The acquisition of transmission zeros can be achieved by means of cross coupling,source-load coupling.The main work of this paper is to study the design of a high selectivity bandpass filter with transmission zero by combining the SIW technology and cross coupling and the source-load coupling.Firstly,this paper briefly introduces the current status of the filter and its basic theoretical knowledge,including the classification and basic parameters.Secondly,the paper also explains the carrier of the filter desiging,namely SIW,in this paper,introduces and analyzes its basic structure and characteristics in detail,and introduces two common transition structures of SIW between microstrip lines,and then illustrates the three common kinds of coupling structure between the SIW cavities,all of which provide a theoretical basis for the design of high selectivity filters by combining SIW with cross coupling theory.Thirdly,the cross coupling theory is introduced,and the phase models of the three resonators coupling(Coupled Triplet,CT)and the four resonators coupling(Coupled Quadruplet,CQ)are introduced in detail.In addition,the position changes of TZ are discussed,and the phase model of CT structure is verified through a simulation example.Then,the effect of second mode resonator on the TZ of CT structure is discussed with a simulation example.In the end,a high selective bandpass filter with a transmission zero point on either side of the passband is designed by using the above method and SIW,which uses a metallic via-holes to disturb first order mode.Finally,in order to obtain a better frequency selectivity filter,this paper combines the SIW miniaturized resonator design idea with the source-load coupling theory and the band-stop resonator to design and process two filters with quasi ellipse filter response.The three filters designed in this paper have better frequency selectivity characteristics,and the experimental results is in good agreement with the simulation ones,and all the research is worthy.