ALMA MEMO 551 Cross-polarization characterization of GORE–TEXr slabs at band 9 frequencies

GORE–TEXr material, commonly used in radomes, is known to be transparent at microwave bands [1]. In ALMA a thin GORE–TEXr membrane will cover the aperture through which the RF beam enters the cabin at the primary vertex hole [2]. Slabs of GORE–TEXr are also generally employed in windows for intermediate temperature shields inside the cryostat. The purpose of these windows ideally is to allow the beam to pass through them without introducing any alteration of the beam properties. Main concern has to be put on RF loss, but also in cross-polarization efficiency degradation. This report will stress on the results we have obtained in relation of loss of cross-polar efficiency of a linearly polarized beam passing through a GORE–TEXr slab, depending on its orientation relative to the direction of polarization of the beam. Polarization properties of Muporer and Rohacellr were also investigated.