W-band prototype of platelet feed-horn array for CMB polarisation measurements

We present the design and performance of a 2x2 prototype array of corrugated feed- horns in W-band. The module is fabricated using a so-called “platelet” technique by milling Alu- minum plates. This technique is suitable for low-cost and scalable high performance applications. Room temperature Return Loss measurements show a low (< −30 dB) reflection over a 30% band- width with a maximum matching of -42 dB at 100 GHz for all four antennas. Beam pattern mea- surements indicate good repeatability and a low (-25 dB) sidelobe and crosspolarisation levels. This work is particularly relevant for future Cosmic Microwave Background polarisation measurements, which require large microwave cryogenic detector arrays coupled to high performance corrugated feed horns.