The effect of slowly varying surface errors in large millimeter wave antennas: A practical verification in the Itapetinga 45-ft reflector

The aperture efficiency of the 45-ft Itapetinga reflector was found to be about 50 percent at
\lambda = 7
mm. The reflector surface panels were mechanically measured in 2664 points displaying the presence of slowly varying errors that negligibly effect the aperture efficiency. We confirm that the reflector's aperture efficiency seems to be predictable from mechanical measurements of the surface when the distribution of errors is non-Gaussian, when the surface is only slightly rough in terms of a wavelength, and when the slowly varying errors across the surface are known [1], [2].