Surface-wave leakage from substrate integrated waveguide on grounded dielectric substrate

This paper presents the surface-wave leakage from a substrate integrated waveguide (SIW) on a grounded dielectric substrate, which propagates the TM₀ mode at the lowest order. The hybrid generalized scattering matrix (GSM) formulation, describing the electromagnetric field inside the rectangular waveguide walls, combined with the finite-element method(FEM), accurately depicting the fields surrounding the microstrip and distributing alongside the infinitely extended grounded substrate, establishes a rigorous formulation to tackle the periodic structure. The resulting lowest order dispersion characteristics show very good agreement with those of the TE₁₀ mode of an ideal rectangular waveguide, when the gap between the posted walls is approaching one thousandth posted wall´s diameter. Careful investigation of the electromagnetic field in the plane parallel to the ground plane shows that the leakage is 1) a TM₀ surface mode, and 2) significant near and below the cutoff frequency of the rectangular waveguide section of the SIW.