Millimetre-Wave Characterisation of an Embedded Reflective Half-Wave Plate for Spaceborne Cosmic Microwave Background Polarisation Measurements

As a part of a European Space Agency critical enabling technology programme, we are developing a large 1.2 m diameter reflective half-wave plate polariser for use in a spaceborne cosmic microwave background B-mode polarisation detection experiment. From an initial study phase we have established the polariser radio frequency performance requirements and present these along with corresponding room temperature measurements of a sample device in the frequency range 75-350 GHz. We briefly describe our measurement setup, and a new cryogenic facility that is being developed to allow low temperature performance measurements of device samples. Data acquired to date show that the polariser exhibits a near 150% bandwidth and meets key performance specifications associated with transmission, modulation efficiency and cross polarisation discrimination