A probe-fed air-substrate patch antenna with an inclined radiating patch for generating a downtilt main beam for WLAN operation in an on-wall access point is presented. The proposed antenna has a simple structure and consists of two major parts: An L-shaped ground plane and an inclined radiating patch, which is easy to implement. Constructed prototypes suitable for operating in the 2.4GHz WLAN band are demonstrated. Results indicate that, simply by varying the inclination angle of the radiating patch, a downtilt main beam with a wide range of downtilt angles can be achieved. In addition, by selecting the proper inclination angle of the radiating patch, the proposed antenna shows a narrower 3-dB beamwidth in the elevation plane, resulting in an enhanced antenna gain, which is very suitable for on-wall 2.4GHz WLAN access point applications. Details of the proposed antenna design are described, and experimental and simulation results are presented.