A method of measuring the surface shape of reflector antennas

As radio astronomers become increasingly interested in observing at millimeter and submillimeter wave lengths, the need arises for the measuring and setting of the surface shape of parabolic reflectors to a higher accuracy than is obtainable using conventional techniques. Typically the accuracy required is greater than 0.1mm. The method described in this paper measures the curvature of the surface with a high accuracy at many points along a radius of the surface. These curvature values are then integrated twice with respect to the distance along the surface by an on-line computer, the result being the Y coordinate of the surface as a function of distance along the radius. This measurement is repeated for different radii, the resultant data being used to generate the best fit parabola to the surface and deviations from this best fit. Measurements made on an 11 meter radio telescope yield results for the RMS surface accuracy that are consistent with the antennas measured performance at millimeter wavelengths. Two separate measurements of the same surface indicate a measurement accuracy of 0.05mm RMS. The time taken to survey the 11 meter antenna was less than 4 hours for 48 radii and greater than data points.