An antenna device including a reflectarray with array antenna elements, and an outer feed provided with a waveguide and a widening funnel which in a widened end carries a waveguide aperture for illumination of the reflectarray. The antenna device eliminates or at least reduces a position dependence of an antenna lobe with respect to frequency. Furthermore, the antenna device presents a low monostatic radar cross section and compactness. To this end the antenna device is fed offset and is provided with a device for movement of a phase center of the antenna with a frequency relative to the waveguide aperture of the feed in the vicinity of the waveguide aperture.