Gregoriansymmetrical reflector
The reflector can be analyzed using the student version of GRASP9 available from TICRA ( using a Gaussian beam feed antenna.  A step-by-step presentation can be downloaded: Gregorian_ppt_audio with an audio track or using GRASP10 Gregorian_10_audio_ppt along with a set of GRASP files: Gregorian_GRASP.  The executable GRANETDS (Linux version) can be downloaded for the geometry parameters. To understand the geometry, see: C. Granet, Designing Axially Symmetric Cassegrain or Gregorian Dual Reflector Antennas from Combinations of Prescribed Geometric Parameters, IEEE Antenna and Propagation Magazine, Vol. 40, no. 2, April 1998, pp. 76-82 and Part 2, Vol. 40, no. 3, June 1998, pp. 82-87. A set of Fortran subroutines for this geometry is contained in the set: granet_equations.