PURPOSE: To minimize the deterioration in the radiation pattern by providing a radome protecting an antenna main body from an external environment and a radio wave absorbing body absorbing a radio wave reflected from the radome and mounted at least to the primary radiator.

CONSTITUTION: A Cassegrain type antenna system consists of a main reflection mirror 1, a sub reflection mirror 2, a primary radiator 3, a feeding part 4, a radome and the radio wave absorbing bodies 13, 14 mounted respectively to the rear face of the sub reflection mirror 2 and the outer face of the primary radiator 3. Denoting the shape of the radome 5 as a sphere, the normal vector at an optional point of the radome 5 passes through the center 12 of the sphere without fail. Since the radio wave 9 radiated from an optional point of the main reflection mirror 1 is radiated in parallel with the mirror axis 16 without fail, the reflected wave 11 of the radio wave 9 crosses the mirror axis 16 without fail. Moreover, the range of the reflected wave 11 to be scattered comes to the outside of a half of the radius of the radome, then the reflected radio wave 11 is absorbed by mounting the radio wave absorption to the part in crossing with the mirror axis 16 within the range.