Shortcomings of cross polarisation methods for reflector antennas

The still increasing requirements to satellite reflector antennas, in particular with respect to such parameters as cross polarisation and side lobe level, imply a demand for fast and accurate analysis methods by which the performance of the reflectors can be predicted. One such approach is the SNFGTD method [Bach et al., (1981)] in which the near field from the reflector is cal­culated on a sphere by using the GTD, and transformed into the far field by using a spherical expansion. In the near field the advantages of ray optics may be fully exploited, since the caustic of reflected rays, which in the far field occurs in the main beam direction, does not exist close to the antenna. For example, the ray description allows a rigorous treatment of blockage from feed or subreflector, simply by tracing the rays through the system, while physical optics (PO) relies on a truncation of the induced currents in shadowed regions. In addition, since the near-field to far-field transformation makes use of the FFT [Larsen, (1980)], SNFGTD will in many cases be superior to PO with respect to computer time.

Publication: 1986 IEEE AP-S Symposium Digest
Place: Philadelphia, PA, USA, 8-13 June, 1986