Propagation and band broadening effect of planar integrated ridged waveguide in multilayer dielectric substrates

To improve the bandwidth of the SIW, a planar ridged substrate-integrated waveguide (RSIW) with a center line of cylindrical posts is proposed. Theoretical design formulas are derived. The bandwidth is defined as between the cutoffs of TE₁₀ and TE₂₀ modes of the RSIW. The modes are made equivalent to those of a transmission line cavity, across the transverse plane, and the cavity is loaded by a ridge of capacitive posts. Good agreements are observed between the theoretical formulas and numerical simulations. A 37% bandwidth enhancement is achieved; in fact, with structures added to increase the post capacitance, still higher bandwidth enhancement is possible.