PURPOSE: To attain parallel grid lines when grids are projected on an antenna aperture via a reflection mirror by forming the grids constituting a polarized wave grid plate as lines not in parallel with each other.

CONSTITUTION: A curved face polarized wave discriminating grid plate 15 is arranged in opposition to a reflection mirror 1 and a primary radiator 3. The curved polarized discrimination grid plate 15 is formed with a part of parabolic ace or elliptic face of rotation, the focus of the curved face polarized wave discrimination grid plate 15 is made coincident with the focus 2 of the reflection mirror 1 and a primary radiator 8 is arranged to the other focus 16 in opposition to the grid plate 15. Since the reflected radio wave in the polarized wave discrimination grid plate 15 is collected to the focus 16, the focus 16 is called a focus of the reflecting mirror 1 which is formed newly by the reflecting operation of the grid plate 15. The shape of each grid is selected so that the projected lines on the antenna aperture 13 are in parallel with each other in projecting the grids of the polarized wave discrimination grid plate 15 onto the antenna aperture 13 via the reflecting mirror 1.