A Ka-band microstip patch antenna with the functions of switchable pattern is presented. The antenna structure is composed of three rectangular patches and four radio frequency microelectro-mechanical system (RF MEMS) switches. The switches are placed to connect the center patch with other two ones, with two switches on the top edge of the center patch and others on the bottom edge. By controlling the states of the RF MEMS switches, the proposed antenna can radiate two patterns. Moreover, the switchable functions are operated at the same frequency band with a bandwidth of 30.9%. Simulated results by Ansoft HFSS are given.