Active S-parameters of an Antenna Array

What is the difference between S-parameters and Active S-parameters in an antenna array?
 
 While S-parameters are perfectly fine for working with single antenna element, it is not enough for an array. Active S-parameters of an array are its S-parameters when all of the antennas are excited, bringing mutual coupling into play. Furthermore, Active S-parameters might significantly change while scanning, decreasing working band.