Comparison of three cross-polarisation prediction methods for reflector antennas

Three analysis methods for reflector antennas, the spherical near-field geometric theory of diffraction (SNFGTD), the moment method (MM) and physical optics (PO) are compared. In the SNFGTD method, the far field from the antenna is found by a spherical near-field transformation (SNF) of the tangential electric near field on a sphere surrounding the antenna once this has been found using the geometrical theory of diffraction (GTD). SNFGTD and MM agree very well, whereas PO differs with respect to the cross-polar pattern. Some discrepancies between SNFGTD and MM are shown to be related to inaccuracies in the GTD diffraction coefficients close to the reflection boundary.