To reduce the sidelobes of a sonar operating in air, a new array signal processing technique using a nonlinear sidelobe canceler is proposed. In this system, complementary beamforming and nonlinear subtraction processing are used to reduce the sidelobes effectively even in the presence of array imperfections. First, the principle of the proposed technique is described. Second, the directivity pattern measured by the experimental system is discussed. Finally, an acoustic image of a life‐size human model target is shown. It is demonstrated that a 3D image of good quality can be obtained. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(12): 13–25, 1999