Compact Dual-/Tri-Band SIW Filtering Antennas Using Cavity-Backed Slots

Compact dual-/tri-band SIW filtering antennas using cavity-backed slots are proposed. By etching a pair of open-loop slots (OLSs) and a slot on the SIW cavity, the slot can be treated as a radiator as well as a resonator. As a result, a dual-band filtering performance with four radiation nulls (RNs) is obtained, achieving high selectivity and good out-of-band suppression. The formation mechanism of RNs is analyzed. To further prove this design method, two pairs of OLSs and a horizontal straight slot are simultaneously etched on the SIW cavity, achieving the tri-band filtering response with 6 RNs in the stopband. Two prototypes are fabricated and tested for demonstration, showing the excellent dual-band filtering response with center frequencies of 4.56 and 5.7 GHz, and the superior tri-band filtering response with center frequencies of 4.1, 4.82 and 5.62 GHz. Moreover, both designs exhibit the compact size of 0.4 ×0.5λ
²
0
due to compact structures.