The applicability of moth-eye structures to THz components is investigated. With the help of RCWA and effective medium theory, optimal structural parameters for one-dimensional and two-dimensional periodical surface-relief gratings are deduced. The required structural parameters are in such order of magnitude that they can be manufactured by ultra-precision machining directly into the surface of the substrate material. Benefiting is that plastic materials, which are preferred materials in THz spectral region, can be accurately manufactured by ultra-precision machining. The application of the moth-eye structures follows directly the primary shaping of the components by conventional manufacturing methods like turning and milling so that no additional materials are necessary. A comparison between several structures fabricated on planar plastic probes is given.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.