Study On Novel Substrate Integrated Waveguide Bandpass Filter

Substrate Integrated Waveguide(SIW)is a new type of waveguide structure,which combines the respective advantages of waveguide and microstrip structure,such as low manufacturing cost,low transmission loss,power capacity and easy integration with other plane structures and so on.In this paper,the relevant theoretical knowledge and the design method of microwave filter are analyzed and the synthesis method of cross coupling filter is introduced.Then the SIW cavity is introduced from the traditional rectangular waveguide,including the transmission properties of SIW,the method of coupling between cavities and the feeding method of the filter.The main contents are as follows:1)The miniaturized bandpass filter using quarter substrate integrated waveguide resonator with elliptic defected structure is presented.Due to the application of quarter-mode technology and the introduction of elliptical defect structure,the sie of the filter is reduced by 88%.The filter possesses a transmission zero(TZ)in the upper stopband,which highly improves the selectivity.2)Inductive window structure with ?-shaped slots is proposed and applied in the circular SIW(CSIW)cavities,which not only enhances the coupling parameters between two cavities but also ensures the integrity of the CSIW resonator.Meanwhile,S-shape slots as the electric coupling structure are firstly used on CSIW filters.With both coupling structures,a third-order CSIW cross-coupled bandpass filter is designed,and a TZ occurs in the lower stopband.Then a fourth-order CSIW cross-coupled bandpass filter is proposed and two TZs are implemented in both sides of the stopband with attenuation of below-40 d B,respectively,which greatly improves the frequency selection performance of the filter.3)The theoretical knowledge of microstrip patch and SIW dual mode structure is analyzed,and then a dual-layer dual mode cavity is proposed innovatively,which is combined by the microstrip patch and SIW.The size of the new dual mode structure is further reduced by more than 50% compared to the traditional SIW cavity.