To provide an inexpensive structure capable of uniformly applying a tension to the insulation sheet of the sheet radome of an antenna.

The antenna is provided with a reflecting mirror, a cylindrical shield panel attached to the opening part of this reflecting mirror, a rear face ring rubber sheet which are successively overlapped on a ring-shaped flange part at the outer terminal of the shield panel, a circular insulated sheet, a ring-shaped rubber sheet, a front face ring, plural bolts for fixing the part of the front face ring from the rear face ring overlapped on the flange part and nuts to be screwed therewith. The inner peripheral part of the rear face ring has a structure having a projecting wire protruded toward the front face ring for a prescribed length and extended over all the periphery of the rear face ring. The front face ring is positioned outside the projecting wire, and the tension of the insulated sheet is changed the compression of a pair of rubber sheets holding the insulating sheet corresponding to the bolts fastening force.