A Holographic Surface Measurement of the Texas 4.9-m Antenna at 86 GHz

An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9-m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 ¿m at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near-field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation.