A low-profile microstrip patch antenna (MPA) with isolation-bandwidth enhancement is proposed via characteristic mode analysis. First, the MPA under different modes is deeply studied. It demonstrates that the unused modes could be suppressed via the loaded pins. Then, by combining the magnetic wall and electrical wall together of two modes via the pins3, the nulls of the electric fields could be shifted to the unexcited port, thus gaining two minimum mutual coupling poles. After that, the length of the radiator is enlarged to move these two poles together for isolation bandwidth improvement in order to reshape the nonbroadside pattern. Finally, our proposed MPA is fabricated and tested. The results illustrate that its 20 dB isolation bandwidth has been widened to about 2.1% ranging from 4.2 to 4.29 GHz. In addition, it still holds the single-layer, single radiator, and low-profile properties.