A low-profile substrate integrated waveguide (SIW) cavity antenna with enhanced bandwidth is proposed. Three slots are etched to divide a single cavity into multiple sub-cavities. Four fraction modes including a half mode, a quarter mode and two-eighth modes are excited by a capacitively coupled feeding. Bandwidth enhancement can be achieved when these fraction modes have close frequencies and couple with each other. A fabricated prototype centred at 3.55 GHz has been measured. With the size of 0.43λ₀ × 0.43λ₀ × 0.04λ₀, the proposed design achieves the bandwidth of 13.5% and an efficiency of 85%. The proposed antenna has advantages of low profile, enhanced bandwidth and high efficiency, which is a good candidate for the fifth generation wireless systems.