Development of surface measuring system for large-diameter antennas using satellite signals.

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Large-diameter high-precision antenmas such as Nobeyama 45 m telescope and IRAM 30 m telescope have been used for millimeter and submillimeter wave radio astronomy. High-resolution surface mesurering techniques are very important to improve the surface accuracy of these antennas. Recently, radio holography is universally used for this purpose. But, the research has been needed to achieve highest possible accuracy in applying this technique to large-diameter antennas used for millimeter and submillimeter wave length.In this Grant-in-Aid for Developmental Scientific Research, a Radio holography system using geostationary satellite signals was developed. The system consists of 2-channel correlation receiver, control system, and softwares for data reduction. As a transmitter, radio beacon signals at 19.45 GHz from the Japanese communications satellites CS-2a and 2b were used. we succeeded in developing the system which has good phase stability, high sensitivity, and good isolation.By the use of this system, the surface of the 45 m telescope was measured 53 times in total in both 64x64 (resolution 86 cm) and 128x128 (resolution 43 cm) measurements in October 1985 and August 1986. Based on the measurements of best repeatability, the surface was adjusted and improved from 200 m rms to 150 m rms. Valuable results were obtained for future developments from the analysis of errors, experiments to reduce the effect of scattered wave, and computer simulations to investigate the effect of pointing error.