E-plane directional couplers in substrate-integrated waveguide technology

In order to analyze and design components in substrate-integrated waveguide technology, it is important that the transitions to interface ports do not significantly influence the component's performance. In this paper, it is demonstrated that the commonly used microstrip-to-SIW transitions are not sufficient to evaluate a SIW structure within a SIW environment. Therefore, we present all-dielectric rectangular waveguide interface ports that considerably reduce the reflections at the transition to the SIW component. These new ports are then applied to the design of SIW E-plane couplers, both with standard dual-circular apertures and as Riblet-Saad couplers. It is demonstrated that SIW couplers with return loss and isolation of much better than 20 dB can be designed. Several 10 db and 3 dB couplers covering the entire Ka-band frequency range are presented. The basic design procedure is validated by comparison with measurements and computations available in the common literature.