Device for calibrating radar measurements, comprising: - a flying drone with multiple rotors, the rotors having axes which are vertical during a hovering flight of the drone, and being distributed angularly about a core block of the drone, in a projection on a reference plane (P ref) of the drone which is perpendicular to the axes of the rotors; - a radar wave reflector, having an overall annular shape about an axis of symmetry (A-A) of the reflector, and such that radar wave reflection properties of said reflector are substantially invariant by rotation about said axis of symmetry; and - means for fastening the reflector to the drone, adapted so that the axis of symmetry (A-A) of the reflector remains perpendicular to the reference plane (P ref) of the drone, and so that the reflector laterally surrounds all of the rotors of the drone, when said reflector is held on the drone by said fastening means, so that the drone and the means for fastening the reflector are at least partially concealed by the reflector, for a radar wave which reaches the calibration device in a direction of incidence that is oblique or perpendicular to the axis of symmetry (A-A) of the reflector, characterised in that an outer surface of the reflector, which faces away from the axis of symmetry (A-A) of said reflector, is one of: - a joining of two crowns (2a, 2b), each being shaped as a respective truncated cone, and an axis of rotational symmetry of each thereof being the axis of symmetry (A-A) of the reflector, both crowns jointly forming a re-entrant angle (α) along a circle of intersection between the two cones, said re-entrant angle appearing in a meridian plane which contains the axis of symmetry of the reflector, and being open opposite said axis of symmetry; - a portion of a sphere, bounded by two planes perpendicular to the axis of symmetry (A-A) of the reflector; - a portion of an ellipsoid of revolution, an axis of rotational symmetry thereof being the axis of symmetry (A-A) of the reflector, and bounded by two planes perpendicular to said axis of symmetry of the reflector; and - a portion of a cylinder of revolution, an axis of rotational symmetry thereof being the axis of symmetry (A-A) of the reflector, and bounded by two planes perpendicular to said axis of symmetry of the reflector. - a flying drone with multiple rotors, the rotors having axes which are vertical during a hovering flight of the drone, and being distributed angularly about a core block of the drone, in a projection on a reference plane (P ref) of the drone which is perpendicular to the axes of the rotors; - a radar wave reflector, having an overall annular shape about an axis of symmetry (A-A) of the reflector, and such that radar wave reflection properties of said reflector are substantially invariant by rotation about said axis of symmetry; and - means for fastening the reflector to the drone, adapted so that the axis of symmetry (A-A) of the reflector remains perpendicular to the reference plane (P ref) of the drone, and so that the reflector laterally surrounds all of the rotors of the drone, when said reflector is held on the drone by said fastening means, so that the drone and the means for fastening the reflector are at least partially concealed by the reflector, for a radar wave which reaches the calibration device in a direction of incidence that is oblique or perpendicular to the axis of symmetry (A-A) of the reflector, - a joining of two crowns (2a, 2b), each being shaped as a respective truncated cone, and an axis of rotational symmetry of each thereof being the axis of symmetry (A-A) of the reflector, both crowns jointly forming a re-entrant angle (α) along a circle of intersection between the two cones, said re-entrant angle appearing in a meridian plane which contains the axis of symmetry of the reflector, and being open opposite said axis of symmetry; - a portion of a sphere, bounded by two planes perpendicular to the axis of symmetry (A-A) of the reflector; - a portion of an ellipsoid of revolution, an axis of rotational symmetry thereof being the axis of symmetry (A-A) of the reflector, and bounded by two planes perpendicular to said axis of symmetry of the reflector; and - a portion of a cylinder of revolution, an axis of rotational symmetry thereof being the axis of symmetry (A-A) of the reflector, and bounded by two planes perpendicular to said axis of symmetry of the reflector.