PURPOSE: To improve the deterioration in a broad angle directivity due to the reflection or diffraction from a support by arranging continuously N sets of composite polygon elements each having a length longer than the wavelength of the operating radio wave, made of a radio wave absorbing material whose projected area to a main reflection mirror aperture is proper to the surface to the support for a primary radiator or the like.

CONSTITUTION: The support I supporting a primary radiator or a sub reflection mirror is equipped with plural composite polygon elements 3 arranged continuously to the face of the main reflection mirror and the length L of the elements 3 in the axial direction of the support 1 is sufficiently longer than the wavelength of the operating radio wave. The length L of each element 3 is selected equal, the surface of each element 3 consists of three planes bent corresponding to the progressing direction 101 of a plane wave 102, and the radio wave absorbing element 2 is provided on the surface. The axial length of said three planes in the axial direction of the support 1 is divided into three with respect to the length L and the length of three divisions is selected to about several times of the wavelength of the operating radio wave. Thus, together with the absorbing action by the radio wave absorbing members 2, the irradiated angle is scattered to the scattered wave at the ridge not absorbed by the elements 2 and the level of the scattered wave liable to be concentrated onto a specific direction is reduced.