Efficient Excitation of an EBG Guide Designed Using a Defect Triangular Lattice of Holes

A triangular lattice of holes is used to design an electromagnetic band-gap (EBG) waveguide for TM modes (magnetic field parallel to the substrate surface and perpendicular to the holes) for operation in the millimeter-wave range. This EBG waveguide can be used in planar circuits, and it is not as bulky as traditional waveguides. A microstrip line was used for the excitation of the waveguide. The dispersion diagram of the triangular lattice is calculated and used in the design of an EBG substrate that operates around 30 GHz. Simulation of the EBG waveguide of 64.05 mm length (equivalent to 21 EBG cells) demonstrated an insertion loss better than 2.5 dB from 28 to 31.5 GHz and return loss below -10 dB across the same band. Despite the lack of complete TM band-gap for such a waveguide, it is demonstrated that signal confinement within the defect region can be obtained by appropriate excitation of the structure. The structure was fabricated and measured, and good agreement between the measured and simulated data was noticed. The observed constant group delay of this waveguide across its operating band implies low frequency dispersion of the structure. Also, the dispersion diagram of the fundamental guided mode is linear, which is an indication of its quasi-TEM nature.