Effects of quasi-optical components on feed-horn co- and cross-polarisation radiation patterns

Astrophysical experiments dedicated to the study of the Cosmic Microwave Background are in needs of very well defined beam shape in order to get an accurate re-construction of the anisotropies power spectrum. These beams have to be carefully designed, but also properly characterised. Some of these instruments will be located in a cryostat for which filters and windows are necessary, and the effects of these additional optical components on the beam shape need to be taken into account. We present here, measurements of such effects on the co- and cross-polarisation radiation patterns of corrugated horns using a Vector Network Analyser.