Negligible Gain Effects of Non-Gaussian Errors Across a Smooth Reflector: Application to the Itapetinga 13.7-M Antenna at 90 GHz

摘要

The aperture efficiency at lambda = 3.3 mm of the 45-ft Itapetinga reflector was found to be of about 25 percent. This radiometric result suggests an equivalent surface accuracy of less than 0.25 mm, r.s.s. (root sum square), assuming a Gaussian distribution of errors, which is much smaller than the actual r.s.s. estimated for the dish (i.e., 0.37 mm, r.s.s.), and represents a 5 dB improvement in gain. This result confirms that non-Gaussian errors across a smooth surface have negligible effects on the aperture efficiency. It demonstrates that there is little effect on gain produced error correlated regions that are small compared to the antenna diameter and that antenna efficiency may be predicted from mechanical measurements when the nature of such errors across the surface is known. It is possible to predict that relatively simple machanical readjustments of the reflector and sub-reflector may raise its efficiency to 30 percent.