In order to reveal the end-effects of a finite grating in pure form, the scattering problem of electromagnetic waves by a semi-infinite strip grating is analyzed, and scattered fields are investigated in the space–wavenumber domain by using the Gaussian-windowed Fourier transform (GWT). The GWT used here is a powerful tool for the space–wavenumber analysis of scattering data, because it can provide better insights into scattering mechanisms that are not immediately apparent in the space domain. In the resultant space–wavenumber displays, the Floquet modes excited by the periodic structure and cylindrical wave diffracted at the edge of the grating are resolved and identified, and their behavior is clearly observed. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 1–8, 2000