In this paper, a novel tri-band reconfigurable patch antenna with simple structure is presented. By changing the on-off state of only two PIN diodes, the antenna can operate in three bands, namely X-band, Ku-band, and Ka-band. The overall size of the antenna is 0.24λL × 0.5λL × 0.019λL, where λL is the free-space wavelength of the lowest operating frequency. A prototype is fabricated and measured to verify the design. The measurement results are in good agreement with the simulation results, which indicate that the proposed antenna can be flexibly switched between three bands of 10.9–11.18 GHz, 15.65–15.9 GHz, and 32.3–33.6 GHz with stable radiation patterns.