A holographic antenna evaluation technique has been developed which allows the electromagnetic measurement of the surface accuracy of a large microwave 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 (mu)m at the surface.; The experimentally measured complex far zone fields are Fourier transformed to yield the aperture plane fields of the test antenna. The surface position of the reflector may be evaluated via geometric optics from the phase of the aperture plane fields. The amplitude information gives the feed illumination pattern and reflectivity characteristics of the antenna.; A series of experiments is 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.
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