PURPOSE: To improve the side lobe characteristic with the use of a radio wave absorbing body in a few number of providing a shield plate nearly coincident with the tangential direction of a mirror surface curve and symmetrical to its axis to the surrounding of the mirror surface curve of a reflection mirror symmetrical around the axis.

CONSTITUTION: Lengths M1, M2 of a shield body 7 are decide by a required angle θ3. Further, a point M4 is a vertical point of a line segment M1, M3 from a focus F. On the other and, a radio wave directing a line segment M3, M4 from the focus F is reflected and made incident in the reflecting mirror 3. The radio wave reflected therein does not propagate toward the wide angle direction. Further, the radio wave incident in the line segment M2, M3 is not propagated toward the wide angle direction and no edge is formed at the point M2, then no diffractive wave is caused. It is at edges M3 and M1 that any diffractive wave is caused. Since the radiation level from a primary radiator placed at the focus F is reduced than a conventional antenna, the quantity of refractive waves is reduced. In using the shield 7 in such a way, the wide angle side lobe characteristic is improved with a few number of radio wave absorbing bodies 8.