Radiation Pattern Measurements and Predictions of the PLANCK RF Qualification Model

PLANCK is one of the scientific missions of the European Space Agency, devoted to observe the cosmic microwave background radiation with unprecedented accuracy. One of the key factors for the performance is the radiation pattern of the telescope, especially the sidelobe performance in the direction of hot celestial bodies like Sun, Earth and Moon. The satellite will operate around the L2 Lagrangian point in deep space under cryogenic conditions. These conditions can not be realized in an antenna test range for a payload of this size. Therefore, the predictions for the performance under flight conditions depend highly on numerical simulations. The model to be used had never before been verified to this level of confidentiality. The challenge was to conduct a test campaign at frequencies up to 320 GHz (far beyond the normal range of the used CATR) with a very large object (the PLANCK RF qualification model with an aperture size of 1.5 m, i.e. more than 1500 wavelength at 320 GHz) to demonstrate sidelobe levels down to -90 dB. A selection of the measurement results and comparison with predictions will be presented.