The geometrical theory of aberrations of classical offset dual-reflector antennas

An increasing number of wide field-of-view antennas (e.g., imaging, scanning, multibeam, etc.) are being made based on classical offset dual-reflector geometries. In spite of this, the aberration theory essential to properly design these antennas remains relatively undeveloped. Despite the excellent work by Dragone (1983) on the diffraction theory of aberrations of offset dual-reflector geometries, a geometrical theory of aberrations is still necessary for a more intuitive understanding of these antennas. In this paper a geometrical theory of aberrations for classical offset dual-reflector antennas is presented. The derivation is based on the optical path length concept and is restricted to comma and astigmatism, which are the two aberrations with dominant impact on the antenna performance.