Invention relates to a radome casing and method for its manufacturing. The radome casing comprises walls (6, 11) of composite material which includes reinforcement fibers (8) and matrix resin (19) binding the fibers together. The walls include a radiation transmission window (11) through which the radiation of a radome antenna passes when the radome antenna (2) is mounted inside the radome casing (1). The amount of fibers in the radiation transmission window (11) is reduced to be less than 40-5% of the amount of fibers elsewhere in the casing walls (6). The reduction of reinforcement fibers in the radiation transmission window (11) reduces attenuation of the high frequency radiation.