Quasi-optical cruciform substrate integrated waveguide (SIW) coupler for millimeter-wave systems

A new substrate integrated waveguide (SIW) coupler in the form of a cruciform structure is proposed and developed in this work. This coupler is composed of four arms waveguide section connected by a central junction. The central portion is partially etched to act as an impedance transformer and mirror. This coupler could be used for millimetre-wave and sub-millimetre wave applications without insuperable tolerance problem. A 3dB coupler design procedure is validated by electromagnetic -simulations (HFSS) and prototype experiments. Measured results on the basis of the realized prototypes agree well with theoretical predictions and simulated results. This coupler is demonstrated to have a 20% relative bandwidth with 20dB of isolation and return loss.