Investigations On The Discontinuities Of Substrate Integrated Waveguide

Transmission line is a fundamental part of microwave techonology. From a historical view, all kinds of new-emerged guide-wave structure depend on the demand of industry of the ages. Rectangular waveguide and microstrip-line are the good evidences. Modern information technologies demand more densely integrity as well as less dissipation for a system. Planar circuits fit for hybrid integrity, cause active components could be easily mounted on them. But disadvantages exist. The dissipation loss caused by conductor, radiation, and dielectric prohibit them to be used in millimeter wave applications. On the other hand, non-planar structures could compose high quality passive components, but hard to be integrated. The substrate integrated waveguide (SIW) borrow advantages of both kinds of guide-wave structure above. The basic concept of SIW is that it use the top and bottom layers of metal together with two rows of via through the substrate to construct a whole waveguide. As the distance of each row of vias is very small compared with wavelength, the dissipation loss of radiation is very small. It acts like a rectangular waveguide filled with some dielectrics. The advantage of such a SIW is that it could avoid the poderosity of metal one. It is also very easy to be integrated in hybrid circuits.The transmission property and many kinds of discontinuity of SIW were discussed in this paper. The methods used to analyze such structure were Finite Difference Method (time domain method and frequecy domain method), Method of Moment and Mode-Matching Method. Some analysis results of commercial software were also referenced. We have made experiments on nearly all kinds of them as well.We studied the transmission property of SIW at first, by both approximate closed-form function and finite difference method. The influence of via dimension on both transmission constant and dissipation factor were presented as a direct result. Many measurements were taken then to verify the dissipation loss of SIW with unit length. The comparing data with microstrip line was also provided. As the latter was used extensively in integrated circuits, we analyzed the transformer between it and SIW in detail. Theoretical study for the impedance matching between them was given. Based on such analysis we designed two types of directional coupler, i.e. narrow wall and broad wall apperture coupler. Experiments have been made to test them. Other types of discontinuity we have studied include: coax and SIW transformer; SIWs' coupling on different layers; branch coupler based on SIW; post inside SIW; the H-plane discontinuity ; bend structures; cross structures; 'Y' branch of SIW etc. Based on such theoretical and experimental studies, we presented the properties of those discontinuable structures and provided a basis for the designing integrated circuits of SIW.