Measuring the CMB spectral distortions with COSMO: the multi-mode antenna system
| Autor: | Manzan, E., Albano, L., Franceschet, C., Battistelli, E. S., de Bernardis, P., Bersanelli, M., Cacciotti, F., Capponi, A., Columbro, F., Conenna, G., Coppi, G., Coppolecchia, A., D'Alessandro, G., De Gasperis, G., De Petris, M., Gervasi, M., Isopi, G., Lamagna, L., Limonta, A., Marchitelli, E., Masi, S., Mennella, A., Montonati, F., Nati, F., Occhiuzzi, A., Paiella, A., Pettinari, G., Piacentini, F., Piccirillo, L., Pisano, G., Tucker, C., Zannoni, M. |
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| Rok vydání: | 2024 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | In this work, we present the design and manufacturing of the two multi-mode antenna arrays of the COSMO experiment and the preliminary beam pattern measurements of their fundamental mode compared with simulations. COSMO is a cryogenic Martin-Puplett Fourier Transform Spectrometer that aims at measuring the isotropic y-type spectral distortion of the Cosmic Microwave Background from Antarctica, by performing differential measurements between the sky and an internal, cryogenic reference blackbody. To reduce the atmospheric contribution, a spinning wedge mirror performs fast sky-dips at varying elevations while fast, low-noise Kinetic Inductance detectors scan the interferogram. Two arrays of antennas couple the radiation to the detectors. Each array consists of nine smooth-walled multi-mode feed-horns, operating in the $120-180$ GHz and $210-300$ GHz range, respectively. The multi-mode propagation helps increase the instrumental sensitivity without employing large focal planes with hundreds of detectors. The two arrays have a step-linear and a linear profile, respectively, and are obtained by superimposing aluminum plates made with CNC milling. The simulated multi-mode beam pattern has a $\sim 20^{\circ} - 26^{\circ}$ FWHM for the low-frequency array and $\sim 16^{\circ}$ FWHM for the high-frequency one. The side lobes are below $-15$ dB. To characterize the antenna response, we measured the beam pattern of the fundamental mode using a Vector Network Analyzer, in far-field conditions inside an anechoic chamber at room temperature. We completed the measurements of the low-frequency array and found a good agreement with the simulations. We also identified a few non-idealities that we attribute to the measuring setup and will further investigate. A comprehensive multi-mode measurement will be feasible at cryogenic temperature once the full receiver is integrated. Comment: To appear in Proceedings of the SPIE Astronomical Telescopes + Instrumentation, 2024 |
| Databáze: | arXiv |
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