Interferometric measurement at 1415 MHz of radiation pattern of paraboloidal antenna at Dwingeloo radio observatory

The complete radiation pattern of a 25-m diameter radio telescope has been measured at 21-cm wavelength to a level of 60 dB below the main beam response. Strong cosmic radio sources with known flux density were used as a signal source. The measurement employed an interferometer consisting of the radio telescope and a 7.5-m diameter reference antenna. By changing the orientation of the telescope, while keeping the reference antenna pointed at the source, the output voltage of the interferometer varies proportional to the field strength pattern of the telescope. This method provides a large improvement in sensitivity over a total power measurement. The paper discusses the theoretical basis of the technique. It describes the layout of the interferometer, the electronic equipment, and the methods of observation and reduction of the data. Some 19 000 points in the pattern were measured. The pattern is displayed by contour plots of equal level. The derived main characteristics of the telescope [1968 AD] at 1415 MHz are as follow: gain
49.0 \pm 0.2
dB, absorption area
282 \pm 8
m
²
, aperture efficiency 0.56, half-power beamwidth
0.57 \times 0.62\deg
. The accuracy and detail allow astronomers to reliably correct radio astronomical observations for the effect of radiation in the sidelobes, spillover region, and feed support scatter lobes. Theoretical calculations of pattern parameters may be checked quantitatively.