Holographic Characterization of the Onsala Twin Telescopes

Paper in proceeding, 2025

Holography is a technique that uses the complex electric field distribution to calculate the aperture amplitude and phase distribution of the Antenna Under Test (AUT). They can be used to infer the aperture efficiency, ray path length, and surface error distributions. We applied this technique to the Onsala Twin Telescope, where we used a geostationary satellite at a low elevation as the source. We used a real-time cross-correlator to obtain the visibilities, which were then inverted to estimate the aperture efficiency and ray-path lengths of both the Onsala Twin Telescopes (OTT). We find that the telescopes have an efficiency of $\sim$\,43$\%$ and 40\,$\%$, and a rms ray path length $\sim$ $\leq$ 1.5 mm. The decoupling of the effect of primary, secondary, and feed is currently underway. Further measurements at different elevations will be presented in the future.