Dual-Band Filtering Antenna Based on Single Square Substrate Integrated Waveguide Cavity

A dual-band filtering antenna (filtenna) with small frequency ratio is constructed in a single square substrate integrated waveguide (SIW) cavity. Two diagonal slots and two perpendicular slots are corroded on the top metal layer, thus three quarter-mode cavities and two eighth-mode cavities are achieved. Three quarter-mode cavities are coupled to form the lower working band of the filtering antenna. Two eighth-mode cavities are designed for the higher working band of the filtennas. As a demonstration, a dual-band filtennas with central frequencies of 6.4 GHz and 6.9 GHz is designed. Three radiation nulls are obtained at $6.1 \mathrm{GHz}, 6.75 \mathrm{GHz}$ and 7.0 GHz.