Repetitive radio reflector surface deformations

Holography measurements of radio reflector surfaces have revealed temperature induced panel buckling. This buckling is a typical example of repetitive deformations which are not covered by the theory of systematic wavefront deformations, for instance of Zernike polynomial type. We present examples of repetitive surface deformations, and explain the corresponding beam patterns. The loss in main beam (on-axis) efficiency from repetitive deformations can be derived from the associated effective rms-value used in the Ruze relation; the full beam pattern can be derived from an exact diffraction calculation. We provide an example which shows that panel buckling affects the beam pattern of the IRAM 30-m telescope, at the shortest wavelength of observation.