PURPOSE: To reduce the deterioration of performance by providing a radome to an aperture of a conical horn, arranging a dielectric rod to the front face of the radome, and constituting the dielectric rod so as to be turned thereby eliminating rain and snow adhered to the radome of a primary radiator.

CONSTITUTION: The dielectric rod 9 is arranged to the front face of the radome so as to eliminate rain and snow thereby attaining reception at all times. The type of material for the dielectric rod 9, the same for the radome 7, should have excellent transmittivity to a radio wave and the width should be as narrow as possible. Moreover, the dielectric rod 9 is so constructed that it is turned via a slot of the conical horn 8 having the slot. A wind force turns the rod 9 and a wind pressure of a parallel flat plate 10 in parallel with the direction of the dielectric rod 9 progresses the turning. The dielectric rod 9 is installed with a slight gap from the surface of the radome 7 and the turning of the rod eliminates adhered rain and snow, allowing to receive a radio wave stably.