Research On SIW Multimode Resonator Based Filtering Circuits

At present,microwave wireless communication systems are advancing rapidly in the direction of miniaturization,high integration,multi-system,multi-function and low-cost.Substrate Integrated Waveguide（SIW）technology has attracted much attention for its merits of high performance,low cost and easy-to-integrate.However,the circuit based on SIW technology is too large to meet the demanding requirements of miniaturization of modern wireless systems,because the width of SIW is limited by SIW cut-off frequency.Under such circumstances,this dissertation makes a profound study of SIW.Based on the theoretical analysis of multi-capacitively loaded SIW multi-mode resonators,a series of methods for their applications in miniaturization and high-performance microwave passive devices are proposed.And a series of microwave passive devices with compact structure,high-performance and self-packaging characteristics are designed,including bandpass filters,multiband filters,filtering crossovers and duplexers.The main work can be summarized as follows:First of all,the transmission line transverse resonance analysis method is used to qualitatively analyze the proposed multi-capacitively loaded SIW multi-mode resonator for the first time in this dissertation.The conclusions of the analysis are verified by EM-simulations,and the characteristics of capacitively loaded resonator and the resonant mode control method are summarized.Then according to the conclusion,a miniaturization and wideband filter based on dual-capacitively loaded（DCL）SIW multi-mode resonator is designed.Its 3d B fractional bandwidth（3d B-FBW）is 20%and the circuit area is 0.64λ_g².Then,a miniaturization and wide-band SIW four-mode bandpass filter is designed with a four-capacitive loading structure.Its 3d B-FBW is 25%and the circuit area is only 0.37λ_g².The realization of these two circuits indicates that the multi-capacitively loaded SIW multi-mode resonator has a broad prospect in the application of filter miniaturization.Secondly,to solve the problem of the narrowness of upper rejection-band encountered in the multi-capacitively loaded SIW multi-mode filters,a DCL-SIW triple-mode resonator with T-shaped grounded striplines is proposed.Two identical T-shaped grounded striplines are employed as DCL structure.A transmission zero is inserted into the high-frequency stopband by using the resonance characteristics of the stripline,and its position can be controlled by changing the length of the open-end arms of the T-shaped stripline.When the transmission zero coincides with the resonant frequency of TE₂₀₁,the parasitic passband of TE₂₀₁ mode is suppressed,thus widening the high-frequency stopband.So,a wideband bandpass filter with miniaturization,self-packaging and wide high-frequency stopband is designed.Its 3d B-FBW is 24%,the highest rejection frequency of upper rejection-band reaches2 f₀,and the area is only 0.55λ_g².This method has guiding significance for developing miniaturized SIW filters with wide stopband characteristics.Thirdly,to overcome the poor selectivity of band-pass filter based on SIW basic mode,a new method of designing the filter by using a stripline hybrid SIW resonator is proposed.On the basis of this method,a three-mode band-pass filter using stripline hybrid traditional SIW resonator is successfully implemented.This filter uses stripline resonant mode and traditional SIW high-order resonant mode to expand the bandwidth while two transmission zeros are inserted on both sides of the filter passband to improve the selectivity.To further improve the filter performance,two band-pass filters are designed based on the stripline hybrid DCL-SIW resonator.Because the basic mode TE₁₀₁ is used,the circuit sizes of two bandpass filters are effectively reduced,they are only 0.48λ_g² and3d B-FBWs are both over 25%,characterized by miniaturization,high selectivity and wide-band,especially suitable for high-density integrated wireless communication systems.Then,to realize the passband flexible control,high-selectivity and miniaturization of the SIW multi-band-pass filter at the same time,a design based on single-capacitively loaded SIW resonator is proposed for the first time.On the one hand,the flexibility of filter passband control is improved by using the flexible characteristics of capacitively loaded SIW resonator resonant mode control.On the other hand,the two resonators are stacked back-to-back,which can generate several transmission zeros in its stopband.This not only improves the stopband suppression,but also suppresses parasitic passband and widens the high-frequency stopband width.The SIW dual-pass-band filter and three-pass-band filter designed by this method have four transmission zeros and seven transmission zeros respectively.In addition,they have the advantages of flexible passband control,wide upper rejection-band and compact size,so that they are very suitable for multi-standard wireless communication systems that have an urgent need for the different of passbands.Finally,the orthogonality of TE mode and TEM mode is used to design filtering crossover to reduce the size of SIW filters and duplexers.DCL-SIW triple-mode resonator is applied to design filtering crossover with miniaturization and wideband for the first time.As a result,a compact wideband SIW filtering crossover is realized with its channel No.1 designed with bandpass response and channel No.2 designed with all-pass response.And another filtering crossover is realized with its both channels designed with bandpass response.The areas of these two SIW filtering crossovers are only0.55λ_g²,3d B-FBWs are more than 20%and channel isolations are higher than 25d B.Furthermore,according to the high-isolation,low-insertion-loss and spatial multiplexing of SIW filtering crossover,a novel design method is proposed,which is using the SIW filtering crossover to build a miniaturization SIW duplexer.This SIW duplexer is realized with an area of only 1.26λ_g² and channel isolation higher than 25d B.The proposed method holds a leading role in the development of miniaturization SIW filtering crossovers and diplexers.