The pointing calibration of the Haystack antenna

We have applied techniques of optical astronomy to calibrate the pointing of a high-resolution pencil-beam antenna by using radiometric measurements of cosmic radio sources. The Haystack antenna, a 120-ft paraboloidal reflector on an azimuth-elevation mount, was calibrated at a frequency of 15.25 GHz. The beamwidth at this frequency is 36 millidegrees; the rms residual pointing error after calibration was 2.90 millidegrees in azimuth and 3.45 millidegrees in elevation. A total of 172 measurements of pointing error were made on eight sources, and these data were fitted by the method of least squares to determine seven instrumental parameters that take into account axis-alignment errors and gravitational effects on the antenna structure. These techniques are not restricted to antennas used as radio telescopes, and they may be useful in the pointing calibration of other antennas.