| In recent years,the speed of updating the communication system is very rapid.At the 7th World Military Games,5G communication has begun to emerge.As a key frequency selection device in the communication system,the filter plays a decisive role in the performance of the communication system.The dual-passband filter has two passbands that can work simultaneously,which can meet the requirements of large-capacity and multi-band communication of 5G communication systems,and thus has been favored by scholars at home and abroad.As a perfect combination of waveguide and microstrip line,the substrate integrated waveguide has high power capacity and low loss,and is widely used in various filter designs.The main work of this thesis is to propose two kinds of four-mode substrate integrated waveguide resonators,and design two 5G mid-band dual-passband filters according to these two resonators.The main research contents are as follows:1.An air-filled substrate-integrated waveguide dual-band filter is designed.Air-filled type refers to the type of mode coupling structure in the substrate integrated waveguide resonator,in other words,by replacing the substrate medium of the intermediate portion of the substrate integrated waveguide resonator with air,a quadruple-mode substrate integrated waveguide resonator having two pairs of degenerate modes is obtained.Under the action of the air region in the middle part of the whole cavity,two pairs of degenerate resonance modes are obtained in the cavity,namely the even mode and the odd mode of TE102,the even mode and the odd mode of TE104,so the resonance can be adopted for dual-band filter.In addition,even and odd modes that are similar to the resonant frequency of TE 104 and that also excite TE 202 are also found,this mode acts as a clutter to interfere with the second pass band.By the short-circuiting effect of the metallized via added at the strongest electric field of TE202 on the electric field,the interference of the clutter TE202 is suppressed to some extent,and adjustment of passband ratio is realized by adjusting the position of the added metallized via.Finally,the transmission zero point of the filter is analyzed,and the method of controlling the transmission zero position is obtained,which is applied to improve the out-of-band rejection.The designed dual-band filter has compact structure and small insertion loss.2.A substrate integrated waveguide dual-band filter based on metallized via mode coupling is designed.By adding a row of metallized vias on the long-side midline of the substrate integrated waveguide cavity,a quadruple-mode cavity with two pairs of degenerate modes is obtained.Two pairs of degenerate modes in the cavity,the even and odd modes of TE102,the even and odd modes of TE104,can be used to form the two passbands of the dual-band filter.After solving the electric field distribution of the clutter TE202 in the resonant cavity,it is found that the clutter can be suppressed by the metallized via on the midline,and the clutter problem is solved.In the frequency response of a dual-passband filter with a center frequency of 3.5GHz and 4.9 GHz directly designed using such a quadruple-mode resonator,the problem of poor out-of-band suppression of the upper sideband of the second passband was found.By improving structure of the filter,the transmission zero near the second passband is obtained,and the out-of-band suppression of the upper sideband of the second passband is greatly improved.In addition,a perturbation metallization via is introduced at the weakest point of the electric field of the second passband operating mode TE104,and a method of independently adjusting the operating frequency of the first passband is obtained.Based on the above improved method of improving the insertion loss and independently adjusting the operating frequency of the first passband,a substrate-integrated waveguide dual-band filter with low insertion loss and independently controlled first passband is designed. |
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