In this paper, a compact structure-shared dual-mode open waveguide antenna (OWA) is designed with a binary dipole array (DA) fed by substrate integrated waveguide (SIW). The dual-mode resonance of OWA comes from its open-ended cavity and coaxial feeding probe which works as a monopole antenna. The OWA occupies 3.80-4.88 GHz, about 28.3% at the center frequency. And the binary DA fed by SIW with constant-amplitude and invert-phase excitation operates at 5.78-6.48 GHz. Furthermore, the binary DA is integrated in one broadside wall of the waveguide. With this topology, the isolation between OWA and DA is greater than 20 dB due to orthogonal polarization.