Metrology of reflector antennas: A historical review

The emergence of radio astronomy, space research, and satellite communication after World War II created great activity in the design and construction of reflector antennas of increasing size and precision, compared to the small radar antennas of the war period. With few exceptions, the reflectors consisted of a set of panels, typically a few square meters in size, that were supported on a backup structure. To be an effective reflector, the shape needs to obey the prescribed contour with a precision of about one-twentieth of the shortest operational wavelength. This was achieved with the aid of a continuously improving array of metrology methods, from the original geodetic theodolite-tape to current laser-trackers, digital photogrammetry, and radio holography. We review the historical development by summarizing the different methods and illustrating their applications with examples, mainly from the field of radio astronomy. It is here where the largest and most precise reflectors have been installed, and metrology has been pushed to a level where a reflector of 100 m diameter can be realized with a surface error of about 250 μm, and a 12 m diameter submillimeter telescope with an error of about 10 μm. The reference list is not exhaustive: it covers major papers of a general nature and detailed descriptions of the examples presented in the text. Table 1 provides a list of the acronyms used in the paper.