A circular patch antenna based on open elliptical-ring slots and shorting vias with conical radiation patterns is proposed. Fed by the coaxial probe at the center of the circular patch, the proposed antenna is excited at three resonant modes, simultaneously. The first resonant mode (monopolar patch mode) is achieved by six shorting vias, each of which is placed at the center of the open elliptical-ring slot. By embedding six open elliptical-ring slots on the patch, the other two resonant modes of the open elliptical-ring slot resonator, TE110 and TE210 can also be excited.