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arXiv · 2406.04664

Planar near-field measurements of specular and diffuse reflection of millimeter-wave absorbers

Fumiya Miura·Hayato Takakura·Yutaro Sekimoto·Junji Inatani·Frederick Matsuda·Shugo Oguri·Shogo Nakamura
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Abstract

Mitigating the far sidelobes of a wide field-of-view telescope is one of the critical issues for polarization observation of the cosmic microwave background. Since even small reflections of stray light at the millimeter-wave absorbers inside the telescope may create nonnegligible far sidelobes, we have developed a method to measure the reflectance of millimeter-wave absorbers, including diffuse reflections. By applying the planar near-field measurement method to the absorbers, we have enabled two-dimensional diffuse-reflection measurements, in addition to characterizing specular reflection. We have measured the reflectance of five samples (TK RAM Large and Small Tiles and Eccosorb AN-72, HR-10, and LS-22) at two angles of incidence in the frequency range from 70 GHz to 110 GHz. Compared with conventional horn-to-horn measurements, we obtained a consistent specular reflectance with a higher precision, less affected by standing waves. We have demonstrated that the angular response and diffuse-to-specular reflectance ratio differ among various materials. The measurements also imply that some absorbers may affect the polarization direction when reflecting the incident waves.

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Fumiya Miura, Hayato Takakura, Yutaro Sekimoto, Junji Inatani, Frederick Matsuda, Shugo Oguri, Shogo Nakamura. 2024-08-23. Planar near-field measurements of specular and diffuse reflection of millimeter-wave absorbers. https://doi.org/10.1364/ao.531654

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