A pin-loaded patch antenna fed with a dual-mode substrate-integrated waveguide (SIW) resonator is proposed in this letter for enhanced bandwidth and stable high gain. The loading effect of shorting pins on quality factor of the radiator is investigated with characteristic mode analysis at first. As such, the pin location can be properly selected to enhance gain with the least negative effect on bandwidth. A SIW resonator operating in TE110 and TE120 modes is introduced to feed the patch through aperture coupling. The dual modes of SIW resonator increase the resonant order of the antenna with compact size, which significantly widens the bandwidth. Moreover, the undesired high-order mode is well suppressed with the proposed feeding scheme, which further contributes to steady radiation performance. Simulated and measured results demonstrate that the proposed patch antenna has obtained an enhanced bandwidth of 22% and stable high gain up to 11.9 dBi simultaneously.