Study On Miniaturized Balanced Filter Based On Substrate Integrated Waveguide

With the rapid development of wireless communication systems,balanced circuits have received widespread attention due to their strong suppression of environmental noise.The balanced filter based on SIW has become a study hotspot in recent years,but the size has been an important factor hindering its further development.This thesis makes a deep study on the miniaturization of SIW balanced filter.Several single-and dual-band balanced filters with compact structure,high passband selectivity and excellent common-mode suppression are designed by using novel SIW resonators.The main contents of this thesis are as follows:Firstly,by using the dual-mode principle,two perturbed circular SIW resonators(CSIWR)are proposed and applied to the miniaturization design of single-band and dual-band balanced filters.The first filter uses dominant mode and higher-order mode to achieve a single-band differential-mode response,and adopts SIW laminated structure and surface slotlines to reduce the size effectively.At the same time,more than 50 d B common-mode suppression is achieved by using out-of-plane feedings and digging holes in the symmetrical plane.The other dual-band filter adopts a new method of realizing differential-mode dual-band response.The degenerate modes TM₁₁₀ modes in CSIWR are separated by perturbation columns.Balanced excitations are placed at the suitable positions,so that the both modes can be excited in differential-mode operation.This method can effectively reduce the number of SIW resonant cavities used,and a compact balanced filter circuit can be constructed.Secondly,a 45°sector substrate integrated waveguide resonator(SSIWR)with a pair of complementary split-ring resonators(CSRR)etched on the surface is proposed.A compact double-layer dual-band balanced bandpass filter with high frequency selectivity is designed and fabricated.The CSRR with bandpass characteristic and the TM₂₂₀ mode in the resonator realize the differential-mode dual-band response.The introduction of defective ground structure(DGS)and the coupling between modes make the filter produce four transmission zeros near the passband,which improve out-of-band rejection.In addition,good common-mode suppression has been achieved through the balanced structure and optimized feeding positions.Thirdly,a quarter mode circular SIW resonator(QMCSIWR)based on CSIWR is proposed.The cavity size is only one quarter of CSIWR.The structure of QMCSIWR is modified by cutting perturbation so that the filter can achieve better cavity coupling and common-mode suppression.The optimized QMCSIWR is used to design a miniaturized balanced filter with high selectivity.In this filter,the source-load coupling and non-resonant nodes are combined to achieve four transmission zeros on both sides of the passband,which effectively improves the frequency selectivity of the differential-mode passband.Finally,the common-mode suppression within the passband range is improved by capacitive patch loading technology.The thesis has 62 figures,7 tables,and 92 references.