Abstract: A fiber reinforced composite structure for slotted type waveguide antenna, comprising at least one layer of conductive material applied over a mandrel by a known method. Radiating element slots are provided during this process and a laminate of low RF loss material is applied in layers of cloth made from aromatic polyamide fibers having a major fiber direction. A binder material, for example, an epoxy resin is applied and cured thereon as the layers are applied. Alternate cloth layers are applied with the major fiber direction rotated 90.degree.. When the laminate is partially completed, two flanged stiffening ribs are typically placed longitudinally on the top and bottom of the waveguide structure along the surfaces other than that containing the slots. Additional layers of the laminate cover the stiffeners and thereby produce integral mounting structures.