Research And Design Of Miniaturized Microwave Differential Bandpass Filter

With the rapid development of wireless communication system,microwave filters play a more important role.The differential circuit can effectively solve the environmental noise and electromagnetic interference in the system,so the microwave differential filter research has received wider attention.Substrate integrated waveguide（SIW）has been widely studied in filter design because of its advantages on high quality factor,easy processing and high power capacity.Based on the analysis of the theoretical knowledge of microwave filters and transmission characteristics of SIW,the thesis makes a wide study on the differential filterminiaturization.The main contents are as follows:Firstly,based on improved microstrip-slotline structure and dual-mode circular resonant ring,a miniaturized differential filter with etched the defect ground structures（DGS）is designed.The microstrip-slotline structure size is reduced by using the folded slotline,while its good common mode（CM）rejection performance is maintained.By introducing perturbation,a transmission zero（TZ）is generated on each side of the passband.In order to further improve the out-of-band rejection,the DGSs are etched to produce the third TZ.Secondly,based on the quarter SIW resonator（QSIWR）with perturbation and one eighth mode SIW resonator（OEMSIWR）,a double-layer miniaturized cross-coupling differential filter using source-load coupling is designed and processed.Compared with the traditional filter,the filter size is reduced by 79.5%.The perturbation cutting angle is used to achieve a wider suppression on the right side of passband.A CM TZ is generated by using source-load coupling in the DM passband,which greatly improves the CM suppression.Thirdly,based on the novel one-third mode triangular SIW resonator（OTMTSIWR）and one-sixth mode triangular SIW resonator（OSMTSIWR）,a cross-coupling miniaturized differential filter is designed.Compared with traditional OTMTSIWR,it is more suitable to design differential circuit because of its symmetry.The filter size can be futher reduced by combining OSMTSIWR and the novel OTMTSIWR.A TZ is generated on both sides of the passband,and good CM suppression is achieved.Meanwhile,the filter size is reduced by 87%.Fourthly,based on the QSIWR with etched Sierpinski fractal defected structure,a miniaturized cross-coupling filter is designed and fabricated.The filter resonant frequency（f₀）is reduced by applying this novel QSIWR,so the filter size is reduced by 88%.By using cross-coupling,a TZ is generated in the upper stopband,which greatly improves the frequency selectivity.Finally,based on the QSIWR with etched symmetrical isosceles right angled triangle defect structure and OEMSIWR with etched defected fractal-shaped structures,a cross-coupling differential filter is designed.By using this novel QSIWR and OEMSIWR,thefilter f₀ is effectively reduced,so the filter size is reduced by72.5%.A TZ is generated in the upper and lower stopbands by using cross-coupling,and the CM signal is suppressed better in the band.Thus miniaturization and high performance of the filter are realized.