The difference between pesa and aesa is that there is a central emitter which can transmit only one frequency at a moment (but one can switch fast to the next) and the aesa can transmit as many frequencies as the number of modules. You can say that pesa is kind of risc processor while ease is the normal intel. If you have enough speed in switching in the pesa then there is little difference. Pesa can be a powerful radar but the main advantage is lower compexity of the modules.