In this paper, a pattern reconfigurable antenna with four switchable directional beams operating at 2.1 GHz is proposed. Specifically, the proposed antenna consists of a square annular patch and a circular patch placed at the center of the square slot. Based on the characteristic mode analysis (CMA), the desired modes can be excited selectively by placing the feeding ports in suitable positions to form a directional beam at a certain angle. Through switching the on/off states of the feeding ports, four directional beams towards different angles can be realized. Simulation results verify that the proposed antenna can generate four switchable beams with the front-to-back ratio larger than 20 dB.