V. Vechtomov – Ph.D. (Eng.), Associate Professor at «Radio-electronic systems and devices» chair, Bauman Moscow State Technical University
The testing stand with a mirror collimator is designed for high-precision measuring electrical characteristics of large-aperture antennas and aircrafts models’ effective radar cross section in the conditions of enclosed shielded rooms as close as possible to the operating conditions in compliance with all requirements of information protection.
The article gives the description of the mirror collimator’s embodiment designed for operation in the millimeter wave range up to 60 GHz inclusive. Large-sized collimator mirror size 54303200 mm2 in the form of asymmetrical clipping of a paraboloid of revolution is made composite of the 143 aluminum trapezoidal shape segments. Mirror focal length is 3250 mm. The working surface of the collimator mirror segments have been milled on a machining center CBPKF 110/1. The accuracy of the reproduction a given parabolic surface is 15 μm. Area of the segment was determined by the machine amount of RAM. The thickness of the segments was 30 mm.
The developed technology for manufacturing segments almost completely eliminated the aging process leading to distortion of the surface profile. The first process step - rough treating of the segment blank flat surface on the machining center CBPKF 110/1. The second process step - heat treating to remove residual stresses that arise after the milling of the segment working surface. The third process step - precision milling of the segment working surface. The fourth process step - thermal aging of the segment sample. Finished segment sample with the base cooled down in the heat-treatment furnace at a set temperature mode.
In order to evaluate the effect of aging on the accuracy of matching the segment working surface shape of the paraboloid of revolution were carried out test measurements using laser radar MV224 Nikon Metrology in 2012. A collimator segment measurement was carried out twice with the number of data points: 215 pcs. at a pitch of 20 mm and 87,500 pcs. at a pitch of 1 mm. In both cases the root-mean-square error from the theoretical surface profile of the paraboloid was 30 μm.
The results of measurements allowed to confirm experimentally the correctness of the chosen technology for the removal of stresses generated during machining and material aging segments. Evaluation of the segment surface profile enables to state about full functionality of the collimator mirror segments that did not lose their accuracy over more than 25 years. On the basis of the large-sized composite mirror collimator SRI REE BMSTU creates a compact millimeter-wave testing area for trial the characteristics of the antennas at frequencies up to 60 GHz inclusive.