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.