A single-feed shorted triangular patch antenna that can be operated at two different resonant modes is proposed and studied. The major current distributions of the two modes on the triangular patch are similar to those of a normal triangular patch antenna operated at its TM11 and TM 21 modes. Therefore, the proposed dual-frequency antenna can radiate a conical dipole-like pattern and a broadside pattern at the two resonant frequencies, respectively. In addition, the two operating modes respectively have the 10dB-input-impedance bandwidths of 18 and 9.4 %. Details of the antenna designs and obtained results are presented.