Low-Profile Wideband SIW Annular Ring Slot Filtering Antenna Under Multimode Resonance

A low-profile, high-gain, wideband substrate integrated waveguide (SIW) annular ring slot antenna with integrated filtering characteristic is presented in this letter. The proposed design features a single-layer substrate with a low profile of 0.046λ₀, where λ₀ is the free-space wavelength at the center frequency. The antenna structure comprises of a circular patch resonator, a circular SIW cavity, and radial solar-ray-shaped slots. By embedding the slotted circular patch inside the SIW cavity, the antenna excites five resonant modes, closely resembling the TM12 mode of the cavity, thereby enabling wideband broadside radiation. The lower radiation null is generated by the TM02 mode of the SIW cavity, while the higher radiation null results from the mixed coupling effect between the patch and the cavity. Notably, the design allows independent control of both radiation nulls for enhanced filtering performance. To validate the design, a wideband filtering antenna was fabricated and measured, demonstrating an impedance bandwidth of 33.2% and a 3-dB gain bandwidth of 14.2% with a peak gain of 8.7 dBi within the operating band.