Antenna measurements using extraterrestrial sources

This thesis discusses the use of extraterrestrial sources for determining the performance characteristics of large aperture antennas. In particular, it shows that techniques employed in the field of radio astronomy are applicable to the testing of large steerable antennas used in the fields of telemetry, space communications and radar. The subject is covered in considerable detail so that the thesis has special significance for antenna engineers unfamiliar with the techniques of radio astronomy. The thesis shows that the use of extraterrestrial sources for measuring the performance of large antennas is superior to alternative approaches, such as near-field measurements, focused aperture measurements, and far-field measurements involving the use of a balloon, airplane, or satellite. A historical background of extraterrestrial radio emission is presented. This is followed by discussions of the fundamental relationships of radio emission and detection. It is noted that signals from extraterrestrial sources are virtually indistinguishable from noise, with the desired signal varying randomly with time. The effects of atmospheric absorption and refraction on these noise - like signals are examined and the characteristics of emission from the sun, moon, Cassiopeia A, Cygnus A, Taurus A, Virgo A , and various quasars are discussed. Details involving the determination of antenna performance parameters are given including the relationships between the temperature of a source, the temperature of an antenna, the effective area, the aperture efficiency, and the gain of an antenna. Special emphasis is placed on the subject of pointing calibration where it is shown that residual errors after calibration can be as low as 2.90 millidegrees in azimuth and 3.45 millidegrees in elevation. Finally, as summary of the conclusions reached as a result of this thesis is presented.