Design and Analysis of SIW Cavity Backed Dual-Band Antennas With a Dual-Mode Triangular-Ring Slot

Substrate integrated waveguide (SIW) cavity backed dual-band triangular-ring slot (TRS) antennas are proposed for planar integration. First, a low profile dual band 45 $^{\circ}$ linearly polarized (LP) antenna is designed and analyzed. The dual-mode TRS is proposed and developed by simultaneously exciting the mode of the slot and the mode of the patch inside the slot. To minimize the antenna size, the lowest mode (TE110 mode) of the SIW cavity is adopted to excite the TRS. The $-$ 10 dB impedance bandwidth at the higher band is 5.9%, 58.3% wider than that of the conventional SIW cavity backed slot antenna. The interactions of the SIW cavity, the slot mode and the patch mode are analyzed with circuit models and verified by full wave simulations, which provides a new insight into the SIW cavity backed antennas. Then, by exciting a pair of the 45 $^{\circ}$ LP antennas with an SIW coupler, a circularly polarized (CP) dual band antenna with a small frequency ratio of 1.26 is developed. The two antennas are fabricated and tested, and the measured and simulated results agree well.