A stable high-gain and wideband circular patch antenna loaded with shorting pins and fed by dual-mode substrate integrated waveguide (SIW) resonator is proposed in this paper. Firstly, the loading effect of shorting pins on quality factor of circular patch radiator is analyzed by using characteristic mode analysis (CMA). In this way, an appropriate location of shorting pins can be determined to maintain high gain and wide impedance bandwidth. Besides, a SIW resonator operating in TE110 and TE120modes is introduced to feed the circular patch through aperture coupling, which significantly widens the impedance bandwidth the results of simulation show the proposed antenna obtains a stable gain as high as 11.2 dBi and an impedance bandwidth of 17% (3.66-4.34 GHz).