Beam Formation and Beam Degradation

The elaborate technical efforts in the construction of radio telescopes and communication antennas are undertaken to obtain a clean beam and the best power sensitivity. This merits an explanation of the beam (image) formation of a telescope/antenna, at first hand expected to be perfect, in the end, however, always suffering from some degradation because of technical shortcomings and influences from the environment. The knowledge of the origin, the form, and the magnitude of beam degradations is the basis on which the tolerance theory of thermal deformations of a telescope is constructed in Chap. 13. An explanation of the diffraction theory of beam formation is found in the textbooks by Born and Wolf (1980), Love (1968), Rush and Potter (1972), Lo and Lee (1988), Christiansen and Hogbom (1995), Kraus (1985), Baars (2007), Rohlfs and Wilson (1996), Thompson et al. (2001), and others.