A comparison between different techniques based on GTD for calculating radiation patterns of reflector antennas

Two indirect techniques are discussed: the extended aperture integration method and the spherical near-field far-field transformation (SNFT). The aperture integration method has been used extensively in calculating the radiation pattern of reflector antennas. Its accuracy is normally acceptable in calculating the main beam and the first few sidelobes. To calculate the far out sidelobes or to improve the accuracy of the results for the main beam and the first few sidelobes, the edge diffracted fields should be included in the aperture field integration. In the SNFT, the near field of the reflector is calculated on a sphere around the reflector using GTD (geometrical theory of diffraction). Then the far field is calculated from the near field using spherical wave expansion.>