Field strengths of the beacon radio waves transmitted from the geostationary satellite ETS 2 are observed at a midlatitude station in Japan. Regular periodic variations in the field strength with a deep fade-out at the central portion, called quasi-periodic scintillations, are analyzed in terms of the minimum and maximum field strengths during each event. The variation in the field strengths is simulated with irregularity models for a variety of shapes, sizes, and electron densities. The numerical results are quantitatively compared with the observations and suggest that one type of quasi-periodic scintillations is generated by linear irregularities that are elongated perpendicular to the drift direction, while the other types is generated by two-dimensional, disk-shaped irregularities. ¿ American Geophysical Union 1995