  In this paper we describe the design and characterization of the optical
system of LSPE/Strip, a coherent polarimeter array that will observe the
microwave sky from the Teide Observatory in Tenerife in two frequency bands
centred at 43 and 95 GHz through a dual-reflector crossed-Dragone telescope of
1.5 m aperture. In general, optical systems composed by a telescopefeed array
assembly have non-idealities that might limit their ability to perform
high-precision measurements. It is thus necessary to understand, characterize
and properly control these systematic effects. For this reason, we performed
electromagnetic simulations to characterize angular resolution, sidelobes, main
beam symmetry, polarization purity and feedhorns orientation. The results
presented in this paper will be an essential input for further optical studies
and for the LSPE/Strip data analysis. Ultimately, they will be used to assess
the impact of optical systematic effects on the scientific results.
