This letter presents a patch and substrate integrated waveguide (SIW) cavity hybrid antenna with wide bandwidth and high-selectivity filtering response. The proposed antenna is a compact single-layer structure with a height of 0.037 free-space wavelength and composed of one circular patch resonator, one square SIW cavity, and nine metallic pins. The circular patch is internally embedded in the square SIW cavity with a surrounded ring slot and the feeding probe is located in the SIW cavity. Here, the dominant resonant mode of the circular patch resonator (TM) and first two modes of the SIW cavity (TE and TE) are employed to achieve effective radiation from the ring slot under these three resonances. Among them, TM and TE both have broadside radiation performances and thus can be used to achieve wide bandwidth, while TE is utilized to generate a radiation null in the lower stopband. Meanwhile, as the input signal is delivered into the SIW cavity and then coupled to the patch resonator, the mixed coupling occurs between these two distinct resonators and it can introduce another radiation null in the upper stopband. Besides, nine metallic pins can further enhance the frequency selectivity in the lower stopband. For demonstration, a prototype antenna is designed, fabricated, and measured. The measured results agree well with the simulated ones and show a wide bandwidth of about 9.14% at the center frequency of 3.5 GHz with a stable boresight realized gain in the range of 6.40 to 7.30 dBi within the operating band. In addition, two radiation nulls appear at 3.26 and 3.74 GHz on both edges of the operating band.