Design Of HMSIW Bandpass Filter Based On New Coupling Structure

As a key component in wireless microwave and millimeter wave systems,the problem of the contradiction between integration and performance has always been the focus and difficulty of filter design and development,and Substrate Integrated Waveguide(SIW)The proposed structure provides a good way to resolve the above contradictions.The SIW structure not only inherits the advantages of miniaturization,easy integration,and low cost of the planar transmission line,but also has the characteristics of high Q value,low loss,and high power capacity similar to the rectangular metal waveguide.Therefore,the SIW filter technology has been industrial in recent years.The research of related technologies in the field and academic circles is of great significance to the development of microwave systems.In the design process of the SIW filter based on the resonator coupling architecture,usually due to the limitation of its coupling structure(inductive window or weak electric coupling structure),the coupling structure between the resonators mostly adopts the method of loading the inductive window,but due to the limitation of its physical structure,it is difficult to obtain strong coupling coefficients to support the implementation of ultra-wideband filters,which limits the application of SIW technology in resonator-coupled form filter design.Aiming at the above situation,this paper proposes a coupling mode of Half Mode Substrate Integrated Waveguide(HMSIW)based on microstrip direct loading,and studies its characteristics and related filter design techniques.The structure of the new narrow-band bandpass filter,the new ultra-wideband filter and the new dual-passband filter based on the above new coupling structure are given,and the integrated design method is verified.The new coupling structure is applied in the SIW filter with different functional requirements.The main contents and innovations of this paper are as follows:(1)Based on the study of the coupling characteristics of HMSIW resonator field distribution and related field distribution,a novel HMSIW resonator coupling structure based on microstrip direct loading is proposed.The coupling structure is directly loaded with microstrip at the magnetic wall of the HMSIW resonator.The realization of the method is simple in structure design,and can realize flexible adjustment of the coupling coefficient in a wide range(from weak to strong),which provides a new idea for the realization of the filter.(2)Based on the proposed coupling structure,a novel narrowband HMSIW bandpass filter operating in the X-band and a new ultra-wideband HMSIW bandpass filter are designed.The narrowband HMSIW bandpass filter has a center frequency of 12 GHz and a relative bandwidth of 7%.The relative bandwidths of the two ultra-wideband HMSIW bandpass filters are 40% and 51%,the in-band insertion loss is less than 0.4 dB,and the return loss is greater than-15 dB.It is worth noting that the above filters all use the microstrip direct loading coupling structure to realize the coupling of source and load,and generate out-of-band transmission zeros in a limited frequency band,which improves the selection characteristics of the filter.(3)Based on the proposed coupling structure,an HMSIW bandpass filter with dual passband is designed.The dual-pass SIW filter operates at 8 GHz and 14.45 GHz with relative bandwidths of 12.5% and 4.1%,respectively.The coupling of source and load is introduced to generate three outof-band transmission zeros at 10.6 GHz,16 GHz and 17 GHz,which improves the out-of-band rejection level of the filter.