Thanks!
The purpose of doing this estimation is actually for the measurement. However, I would like to be able to understand and analyze the measured RCS.
For this test, the elements in the array are not "real" antennas, but some simple passive scatters such as half wave dipoles. All I want to know is if there is a simple rule of thrum that can tell the total RCS of the array based on the RCS of a single element.
I guess I can try to understand this from simulations.