Toward a Phase Adaptive Stabilization System for Next-Generation Single-Dish Sub-mm Telescope Part - I: Multipath Phase Measurements Based on Ultrastable Microwave Signal Distribution.

Large-aperture, single-dish, submillimeter (sub-mm)-wave telescopes are important to our understanding of the universe, but it is a long-term outstanding challenge to make the single-dish sub-mm telescopes larger while keeping a high accuracy of their surfaces. A bottleneck in the context of the size and the operating wavelengths of such telescopes is the deterioration of wavefront errors (phase shift) due to the deformation of reflective surfaces. Here proposed is a phase adaptive stabilization system (PASS), functioning as an adaptive optics system of radio frequency (RF), an essential tool for overcoming the challenge, which is based on a state-of-the-art ultrastable microwave signal distribution (UMSD) technology. The UMSD system with a phase drift of less than 11 fs rms over 600 s, is especially proposed for the PASS, which is an innovation. The results of outfield experiments have shown that the PASS is sufficiently accurate to measure the changes in the excess path length down to the level of 20 mu m, which is the highest accuracy reported up to now. Our study marks a major step toward the PASS.