Multi-map holography for large crossed-Dragone telescopes

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
² Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
³ Max Planck Institute for Radio Astronomy, Bonn, Germany
⁴ Departamento de Astronomía, Universidad de Chile, Santiago 7591245, Chile
⁵ Departamento de Ingeniería Eléctrica, Universidad de Chile, Santiago 8370451, Chile
⁶ School of Engineering and Natural Sciences, University of Iceland, 107 Reykjavík, Iceland
⁷ Instituto de Astrofísica and Centro de Astro-Ingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Santiago, Chile
⁸ National Radio Astronomy Observatory, Central Development Laboratory, Charlottesville, VA 22903 USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 27 August 2025
Accepted: 8 June 2026

Abstract

We present a novel microwave holography technique for large crossed-Dragone telescopes, which feature two similarly sized off-axis reflectors whose surface deformations must be measured and corrected independently. A major challenge in these systems is the degeneracy of wavefront distortions caused by surface errors on both reflectors, which conventional single-beam holography cannot effectively disentangle. The method addresses this challenge by acquiring five beam maps at distinct focal plane positions and employing an inference-based analysis to reconstruct the individual surface error distributions of the two large reflectors. We developed a fast and accurate beam analysis method based on the Fresnel-Kirchhoff diffraction theorem to accelerate the forward beam calculations. This greatly reduces the computational cost while maintaining high accuracy, enabling a practical application to iterative fittings for the large crossed-Dragone telescopes. The accuracy and feasibility of the new technique have been verified by numerical simulations for the FYST telescope and experimental tests for a 400 mm diameter crossed-Dragone optics.