Measuring the CMB spectral distortions with COSMO: the multi-mode antenna system

E. Manzan; L. Albano; C. Franceschet; E. S. Battistelli; P. de Bernardis; M. Bersanelli; F. Cacciotti; A. Capponi; F. Columbro; G. Conenna; G. Coppi; A. Coppolecchia; G. D'Alessandro; G. De Gasperis; M. De Petris; M. Gervasi; G. Isopi; L. Lamagna; A. Limonta; E. Marchitelli; S. Masi; A. Mennella; F. Montonati; F. Nati; A. Occhiuzzi; A. Paiella; G. Pettinari; F. Piacentini; L. Piccirillo; G. Pisano; C. Tucker; M. Zannoni

arXiv · 2406.09349

Measuring the CMB spectral distortions with COSMO: the multi-mode antenna system

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Abstract

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.

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E. Manzan, L. Albano, C. Franceschet, E. S. Battistelli, P. de Bernardis, M. Bersanelli, F. Cacciotti, A. Capponi, F. Columbro, G. Conenna, G. Coppi, A. Coppolecchia, G. D'Alessandro, G. De Gasperis, M. De Petris, M. Gervasi, G. Isopi, L. Lamagna, A. Limonta, E. Marchitelli, S. Masi, A. Mennella, F. Montonati, F. Nati, A. Occhiuzzi, A. Paiella, G. Pettinari, F. Piacentini, L. Piccirillo, G. Pisano, C. Tucker, M. Zannoni. 2024-06-13. Measuring the CMB spectral distortions with COSMO: the multi-mode antenna system. https://arxiv.org/abs/2406.09349

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