Miniaturized High Performance Planar Bandpass Filter Based On Hybrid Structure

Modern communication system needs miniaturized,easy-integration and high-performance filters,to ensure its normal and stable operation.Substrate Integrated Waveguide（SIW）inherits the advantages of high Q-value and low loss of closed structure well,and can be easily integrated.However,because the SIW cavity is a closed structure,its volume is larger than that of traditional unclosed structures such as microstrip lines and coplanar waveguides.Therefore,thesis aims to reduce the volume of the SIW filter through the hybrid structure of SIW cavity and microstrip line.At the same time,it has high selectivity,high rectangular coefficient,and wide stopband.The main studies conducted in thesis are as follows:1.Aiming at the problem of large volume of pure SIW cavity bandpass filters（BPFs）,a SIW filter based on the hybrid structure of SIW cavity resonator and microstrip resonator is proposed.Based on the traditional box-like coupling topology,additional transmission zeros（TZs）are added by increasing the cross-coupling of non-adjacent resonators.Finally,high selectivity is achieved.In addition,the filter can realize independent control of the TZs on the left and right sides of the passband by controlling cross-coupling and external coupling.2.To avoid the extra loss caused by the introduction of electrical coupling in the design of traditional SIW filters,a coupling topology with high selectivity is proposed by combining the traditional cross-coupling topology with the newly designed suspended-stub structure.To verify this topology,a hybrid microstrip-half-mode substrate integrated waveguide（HMSIW）cavity multilayer filter is proposed.First,a 3^rd-order cross-coupled topology is achieved by stacking HMSIW cavities with different shapes.Subsequently,an annular microstrip resonator is added to achieve the suspended-stub structure.3.To address the difficulty of realizing high-order filters in a compact size for multi-layer SIW filters,a novel multi-layer quarter-mode substrate integrated waveguide（QMSIW）BPF with advantages of miniaturization,high selectivity and wide stopband is proposed.A novel dual-mode microstrip resonator is introduced to connect the QMSIW resonators located on the upper and lower layers with low insertion loss.Moreover,the dual-mode resonator and two QMSIW cavities resonators together achieve a 4^th-order response.At the same time,the filter can achieve flexibly respond by changing the position of the coupling slot.4.To improve the Q-value of the microstrip resonator and realize the low loss microstrip filter,a high selective microstrip filter with SIW cavity shield which can be applied to 5G N78 band is proposed.The added shield can introduce additional capacitance and inductance to the ground,achieving miniaturization,and the shield can also reduce the radiation loss of the filter.This provides new insights for the application of SIW cavities.The above designs are all aimed at the study of the hybrid structure of SIW cavity and microstrip,so that the full-mode SIW cavity,HMSIW cavity and QMSIW cavity can be cleverly combined with the microstrip resonator,which can achieve a small volume and ensure good performance.This provides some reference for the design of miniaturized SIW filters.