Research On Wide Stopband Bandpass Filter Based On Substrate Integrated Waveguid

In recent years,the availability of radio frequency spectrum resources for mobile communication systems has been very limited,which has motivated the development of microwave filters with functions such as frequency selection and suppression of harmonic signals Microwave filters,represented by substrate-integrated waveguide（SIW）bandpass filters,have attracted widespread attention due to their low cost,low loss,light weight,high quality factor,and ease of integration.However,due to the increasingly complex electromagnetic environment,the normal operation of mobile communication systems is severely affected.In order to reduce these interference effects and improve communication signal quality,this dissertation focuses on the in-depth study of wide-stopband SIW bandpass filters,with the following specific work:First,the center position of the internal coupling window offset and the loading of metal via disturbance were designed to repair the intrinsic suppression of the mode.The design method for extending the stopband width and optimizing out-of-band suppression of second-order SIW bandpass filters was studied.Third-order and fourth-order SIW bandpass filters were designed and fabricated for physical verification,with measured stopband widths exceeding2.05f₀（f₀ is the center frequency of the filter）and suppression depths greater than 30dB,verifying the feasibility and accuracy of the design method.Compared with other single-layer SIW wide-stopband filters,this design method is simple,low-cost,and easy to implement.Secondly,in order to further widen the stopband width,two types of electromagnetic hybrid coupling modes,namely,symmetric and non-completely symmetric coupling,are proposed.Based on the theory of electromagnetic hybrid coupling and the intrinsic suppression of modes,two sets of symmetrically distributed coupling holes are etched on the intermediate metal layer to introduce the electric and magnetic coupling amounts of the TE₁₀₃/TE₃₀₁ mode and cancel each other out,thereby suppressing the coupling of this specific mode.The experimental results show that the stopband width is extended to 2.95f₀ and the suppression depth is better than 28dB,which is consistent with the simulation results.In addition,two sets of asymmetric coupling holes are designed to respectively suppress the coupling of TE₁₀₃/TE₃₀₁and TE₃₀₃ modes.The simulation and experimental results show good agreement,and the stopband width is extended to 3.85f₀ with a suppression depth better than 20dB.Compared with the classic fourth-order SIW wideband bandpass filter,the double-layer stacking method is more compact when having the same bandwidth,which is beneficial for integration into microwave circuit systems.Finally,an improved electromagnetic hybrid coupling scheme is proposed,and the ultra-wide stopband performance of a fourth-order SIW bandpass filter is explored.Based on the non-completely symmetric electromagnetic hybrid coupling fourth-order SIW filter,the double-layer stacking is optimized into a four-layer stacking structure,and the coupling slots are etched on the middle metal layer to suppress the coupling of the TE₁₀₅/TE₅₀₁ and TE₃₀₅/TE₅₀₃modes when the offset from the side wall center is approximately 1/10 of the cavity width.The simulation results show that the stopband width is extended to 4.85f₀ with a suppression depth better than 20dB.Compared with other existing SIW bandpass filters,it has ultra-wide stopband performance.In summary,this dissertation explores the wide stopband suppression of substrate integrated waveguide bandpass filters and effectively extends the stopband width,laying a technical foundation for further improving the anti-interference performance of mobile communication systems.