RADIATION PATTERN OF A CYLINDRICAL HORN ANTENNA AND S-PARAMETERS (scattering matrix)
 

Suppose that we have a cylindrical horn antenna with known dimensions.
Supposing that we know the generalized scattering matrix of this
cylindrical horn antenna in a given frequency. This would be a matrix
of dimensions (N+M)x(N+M) considering N modes as input and M modes as
output.
How can one extract the radiation pattern of this antenna in the given
frequency?