A support structure for x-ray windows including carbon composite ribs, comprising carbon fibers in a matrix. The support structure can comprise a support frame defining a perimeter and an aperture, a plurality of ribs comprising a carbon composite material extending across the aperture of the support frame and carried by the support frame, and openings between the plurality of ribs. A film can be disposed over, carried by, and span the plurality of ribs and disposed over and span the openings.