A study of three techniques used in the diffraction analysis of shaped dual-reflector antennas

• Published in: IEEE transactions on antennas and propagation Vol. 37; no. 8; pp. 979 - 983
• Main Authors: Cwik, T.A., Kildal, P.-S.
• Format: Journal Article
• Language: English
• Published: Legacy CDMS IEEE 01.08.1989; Institute of Electrical and Electronics Engineers
• Subjects: Antenna feeds; Antenna radiation patterns; Antennas; Apertures; Applied sciences; Communications And Radar; Exact sciences and technology; Geometrical optics; Lighting; Optical computing; Optical diffraction; Optical scattering; Physical theory of diffraction; Radiocommunications; Reflector antennas; Telecommunications; Telecommunications and information theory; Wave diffraction; Dual reflector antenna; Error; Electromagnetic field; Geometrical theory; Calculating method; Antenna
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/8.34133

An examination is presented of three techniques used for the efficient computation of fields diffracted by a subreflector that has been shaped by geometrical optics synthesis. It is found that these techniques, which are based on the geometrical theory of diffraction (GTD), produce errors in the computed fields that are specific to shaped reflectors. These errors are examined for a reflector system shaped to produce maximum gain from a tapered feed illumination. The discrepancies are directly related to the caustic being located near an observation point of the GTD calculations. The errors found are localized, and they increase in magnitude as the caustic approaches the main reflector. In a general offset geometry, the location of the caustic may be located arbitrarily close to the main reflector given a prescribed output aperture distribution. For the specific case considered here-the common situation of shaping to produce maximum gain-the caustic is located near the edge of the main reflector and on the reflection shadow boundary. A local correction is derived which creates a uniform solution through the caustic and across the reflection shadow boundary. Away from this point the calculation recedes to the standard GTD solution.< >