Analysis of uncontrollable errors on the performance of a large segmented active surface reflector antenna for millimeter wavelengths

Active surface telescopes have become a practical design choice for large reflector systems in which the main optical surface is replaced by a segmented surface with a control system for maintaining a perfect shape. The authors focus on one of the most interesting problems associated with this type of ground-based large active surface radio telescope. This is the effect produced by uncontrollable errors due to gravitational deformation of the antenna structure, and which the active surface control system is unable to compensate for. The impact of these errors must be carefully assessed. First, the authors present a study of the effects of random lateral displacements and uncontrollable rotations of the segments with respect to the nominal position for the purpose of comparison with systematic errors. Second, based on the results of deformation analysis of the antenna structures under gravitational load, the authors assess the effects on the LMT (Large Millimeter Telescope) antenna performance. An analysis of these systematic errors is presented in terms of antenna efficiency and radiation patterns, as a function of elevation.