Fast physical optics simulations of the multi-beam dual-reflector submillimeter-wave telescope on the ESA PLANCK surveyor

We present physical optics simulations of the multi-beam dual-reflector sub millimeter-wave telescope on the ESA PLANCK surveyor designed for measuring the temperature anisotropies and polarization characteristics of the cosmi c microwave background. The telescope is of a non-conventional Gregorian co nfiguration, with two ellipsoidal reflectors providing a very large field o f view at the focal plane where the array of 76 horn antennas feeding low-t emperature detectors is located. We analyse the defocusing effects of the s ystem, the polarization properties of the telescope, and the optical perfor mance of the high-frequency channels based on special muiti-moded horns ope rating at 545 and 857 GHz.