Investigation of the Transition Between Two Different EBG Waveguides

The transition between two different electromagnetic band-gap (EBG) structures is investigated in this letter. A triangular lattice of holes with a partial band-gap was used to design an EBG waveguide for TM modes (magnetic field parallel to the substrate surface and perpendicular to the holes) for operation in the millimeter-wave range. The fundamental guided mode of the designed waveguide has a quasi-TEM nature. This waveguide was designed to serve as a building block of a spatial power combiner and to be excited with an incident plane wave. A square lattice of metal vias was added at the input and output faces of the EBG waveguide to prevent the incident plane wave from penetrating into the triangular lattice of holes and also to enhance the coupling between the guided mode inside the waveguide and the plane wave excitation. The proposed structure was optimized to enhance its transmission characteristics and to increase its bandwidth. The structure was fabricated and measured, and good agreement with the simulation is obtained. It is confirmed that modal fields of the two connecting EBG waveguides match with each other, and this explains the good performance of the structure.