Synthetized beam of QUBIC. Top panel: simulation of the interference pattern on the focal plane generated by a monochromatic point source. Bottom panel: azimuth cut of the theoretical synthesized beam (solid lines) at 140 GHz (blue line) and at 160 GHz (green line) for a detector at the center of the focal plane. Dashed lines represent the beam pattern of a single feed horn. The frequency-dependent position of the secondary peaks is clearly visible.