Research On Miniaturized Multi-mode Substrate Integrated Waveguide Filter

As a device to select specific frequency,filter is an indispensable part of wireless communication,so it has been the focus of scholars in the field of microwave and millimeter wave.According to the structures,filters can be divided into many kinds.The waveguide structure is first developed,and it has the characteristics of low loss and high power.Subsequently,the microstrip structure with simple constructure and easy to process is proposed by some scholars.Substrate Integrated Waveguide（SIW）has the common advantages of waveguide and microstrip structure.It has the characteristics of high Q value,low loss and easy integration of other planar structures.It has attracted the attention of researchers in recent twenty years and is widely used in engineering.With the development of wireless communication technology and the pursuit of miniaturization devices in modern society,the miniaturization technology of filter has received the common attention of engineering and academic scholars.Multimode technology of the cavities as a research direction of the miniaturization of filters has been continuously promoted year by year.Based on the multi-mode theory,this paper designs several SIW filters.The effective use of the structure of metal through-hole,metal blind hole and slot makes the bandwidth of the filter controllable.The idea of cross coupling makes the filter passband meet the design index selectively,and the structure of the multiple filters can meet the needs of miniaturization.Firstly,this paper designed a square triple-mode bandpass filter,which is different from the traditional SIW structure with four holes all around,the structure only has two sides loaded through holes,and so the special boundary conditions enable the TE₁₀₀ mode can transmitted in the filter.Compared with the traditional three mode filter which consider TE₁₀₁01 mode as master mode,TE₁₀₀00 mode cut the volume of the filter.Furthermore,the metal vias and the metal blind hole inside the cavity can disturb the specific electric field of the modes to control the resonance frequencies,and the bandwidth of the filter can be adjusted.The simulation and experimental results verify the reliability and accuracy of the model.Then,a triangular triple-mode half mode filter is researched.The topology is designed to complicated compared to the former filter,and the idea of cross coupling and asymmetric feeders are integrated into each other,resulting in a transmission zeros on both sides of the filter passband,which improves the passband selectivity of the filter.Furthermore,the additional loading microstrip structure at the feed end and the square groove line structure on the ground inhibit the stray mode of the filter,and the filter exhibits good stopband rejection performance.The simulation and experimental results show that the model is feasible.Finally,this paper proposed a SIW dual band pass filter based on the multimode theory.According to the difference of the distribution of the field patterns in the cavity,the metal through-hole is placed at a specific location to adjust some frequency points to form a passband.At the same time,the symmetrical dumbbell shaped slot structure on the surface of the cavity substrate can effectively control the transmission zeros on both sides of the two channels.The insertion loss and return loss of two passbands are good.