Comparison between Milling and Wire Erosion for Manufacturing All-Metal High-Pass Dichroic Mirrors

Ground stations for space communications are often required to operate at different frequency bands, normally spanning from L band to Ka band. In some cases, especially when they are realized according to a beam-waveguide architecture, dichroic mirrors can be used to insert/extract different bandwidths along the propagation of the beam. As these antennas generally operate high-power transmitting channels, all-metal high-pass dichroic mirrors are usually preferred. This paper presents a quantitative comparison between two possible manufacturing techniques for such mirrors, milling and wire erosion, in terms of manufacturing possibilities, accuracy and surface roughness. To this aim, a test case for dichroic mirrors, aimed at installation in the deep space antennas of the European Space Agency to support future missions to the Moon and designed to be as transparent as possible for the K band, is discussed.