By employing the U-slot and feeding network, a low-profile aperture-coupled microstrip patch antenna (MPA) is proposed in this paper. Initial, by etching the U-slot on the patch, the second resonant mode is excited around the fundamental mode of the MPA. Then, a square open-loop resonator is introduced below the aperture-coupled MPA for bandwidth-enhancement, thus exciting the third resonant mode. Finally, this proposed MPA is simulated and discussed. The result shows this antenna has generated the bandwidth for of about 10.57% under radiation of triple-modes. Meanwhile, the antenna also obtains a stable radiation patterns and relative gain of about 5.258 dBi within the whole working band range.