Broadband design method of SIW directional couplers

This paper treats two-fold symmetrical SIW directional couplers with simple structure and broadband characteristics. The proposed directional coupler consists of a rectangular cavity connected four input/output ports at its corner, and several metallic posts inserted within the cavity in order to obtain a desired property. By optimizing the circuit structure, broadband characteristics can be obtained for several directional couplers with a coupling coefficient of 0dB or 3dB. In analysis and design, SIW circuits are treated as waveguide circuits filled with dielectric material, and applied to the H-plane planar circuit approach, the segmentation method, and short-circuiting of fictitious ports. Finally, we demonstrate the validity of this design procedure by em-simulations and measurement of fabricated couplers including microstrip line to SIW transitions.