In this thesis, I describe several advances in the modelling of microwave telescopes.

In particular, my collaborators and I have examined two potential sources of systematic error. The first concerns the non-idealities of a half-wave plate, which we have integrated into the beamconv software. The second is the diffraction of part of the light beam by the large screens that are supposed to hide the ground emission from ground-based telescopes. I also mention a current project that integrates these two aspects together, using beamconv to simulate the noise due to the ground emission.