This paper presents a substrate integrated waveguide (SIW) cavity-backed slot antenna for dual-band operation. By etching a pair of triangular complementary ring slots in the antenna's back cavity for radiation, these slots can effectively excite narrow-gap hybrid modes inside the SIW cavity. One of the modes is shifted upward in the lowest mode (TE120 or TE210 mode) and the other is shifted downward in the highest mode (TE320 or TE230 mode). The two modes appear paired together, which significantly improves antenna performance. The prototype of this antenna is fabricated on a low-cost substrate via printed-circuit-board technology. Simulation results show that the antenna operates in two frequency bands of 11.80?12.50 GHz (0.70 GHz) and 14.50?15.00 GHz (0.50 GHz). It resonates at frequencies of 12.00 GHz and 14.80 GHz, with peak gains of 6.40 dBi and 4.90 dBi, respectively. Additionally, this antenna features a high gain and a stable unidirectional radiation pattern.