An Optimized Transition Structure for Solving Reference Ground Discontinuities in SIW Filter Integration

Substrate integrated waveguides (SIW) have been widely used in the design of highperformance narrowband filters and the integration of microwave circuits in recent years, owing to their high quality factor and easy planarization. In the design of single-board integration, in order to achieve high quality factor and narrow-band SIW filter, a low-cost and effective method is to increase the thickness of the substrate layer within a certain range to achieve lower insertion losses. However, with the switching of the reference ground planes, a discontinuous return path will be induced. Improper handling of the structure will give rise to additional losses and radiation which will lead to EMC issues. In this paper, a method is proposed to extend the inner ground at the discontinuous section to form a stepped transition structure to achieve good signal transmission performance. The simulation results show that at 10GHz, the center frequency of SIW in our design, the proposed transition structure has 1.8dB lower insertion loss as well as 40.14dB higher return loss than the structure of direct interconnection at the discontinuous section.