PURPOSE: To facilitate an easy mass production for the feeder structure of an antenna, by forming a bent rectangular waveguide by covering the groove part of a metallic plate formed with press working with its both open ends by another flat metal.

CONSTITUTION: A metallic plate 1 is formed from a sheet of metallic plate with press working. The plate 1 forms three faces excepting a face formed with a metallic plate 3 among four faces forming the contour of a feeder, i.e. the three faces of a feeder including a primary radiator 5. Then a flange part 2 is fixed to the plate 3 with spot welding, a conductive adhesive, soldering, etc. The sectional form of the radiator 5 must be enlarged toward the radiating port of radio waves since the radiator 5 has a horn shape. Therefore it is required to fold the plate 3. Furthermore it is possible to form the plate 3 with a wire net having meshes suficiently smaller than 1/4 wavelength of a using radio wave. Thus, a feeder structure which facilitate an easy mass production is obtained.