Cassegrainoffset 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: offset_Cassegrain_ppt_audio with an audio track or Offset_Cassegrain10_ppt_audio using GRASP10 along with a set of GRASP files: offset_Cassegrain_GRASP.  The executable GRANETDOF (Linux version) can be downloaded for the geometry parameters. To understand the geometry, see: C. Granet, Designing Classical Offset Cassegrain or Gregorian Dual-Reflector Antennas from Combinations of Prescribed Geometric Parameters, IEEE Antennas and Propagation Magazine, Vol. 44, no. 3, June 2002, pp. 114-123. A set of Fortran subroutines for this geometry is contained in the set: granet_equations.