Design of SIW-Based Multi-Aperture Couplers Using Ray Tracing Method

In this paper, a simplified ray tracing method is used to approximately predict the coupling characteristics of H-plane multi-aperture substrate integrated waveguide (SIW) couplers. The output powers of the output ports are calculated with the reflection and the transmission coefficients at the coupling windows. The ray tracing method provides a simple and efficient way to determine the initial values for the geometrical parameters of SIW-based multi-aperture couplers. From these initial values, the structures of the couplers can be quickly optimized with less iterations, so that the design efficiency can be greatly improved. In order to get high isolation, a criterion is introduced to prevent exciting higher order propagating Floquet modes in the SIWs. Three examples of multi-aperture couplers are designed with our approach. The measured results agree well with the simulated results and the ones predicted using the ray tracing method.