Broadband Planar SIW Cavity-Backed Slot Antennas Aided by Unbalanced Shorting Vias

Two types of substrate integrated waveguide (SIW) cavity-backed slot (CBS) antennas are proposed for bandwidth enhancement. First, a quad-resonance SIW CBS antenna is proposed using a cross-shaped slot and loading unbalanced shorting vias. Additional half-TE₁₂₀ mode is successfully excited along with three other independent modes including half-TE₁₁₀ and odd and even TE₂₁₀ modes. Next, a penta-resonance SIW CBS antenna with a cross-shaped slot is proposed, in which two pairs of shorting vias are loaded. Two additional hybrid modes of half-TE₂₁₀ and half-TE₁₂₀ modes are introduced along with three other independent modes including half-TE₁₁₀ and odd and even TE₃₁₀ modes. Furthermore, the working mechanism of these two types of SIW CBS antennas is explained. Finally, prototypes of these two antennas are fabricated and measured at X-band. Their measured fractional bandwidths are 20.0% and 20.8%, respectively. Simulation and measurement results agree very well, which confirms the validity of the proposed designs.