Examples (one per frequency channel) of the LFI measured beams compared with simulations. The simulated main beams have been computed in the co- and cross-polar basis according to Ludwig’s third definition (Ludwig 1973), in spherical grids with 301 × 301 points defined with respect to the LOS frame. They are referred to the design telescope configuration. In each plot the contours are the levels at  − 3,  − 10,  − 15, and  − 20dB from the corresponding power peak. The simulations have been carried out in the transmitting mode using GRASP9 software. Physical optics and physical theory of diffraction have been used on both reflectors.