I don’t know the differences between those two in game. I know irl they’re absolutely differents, but in-game they look identical. They still uses radar scan sweeps.
AESA is significantly faster, and is able to update targets outside the scan area. mechanical radars are slower, less reliable and can’t update targets outside the scan area
MiGan Fox-3 touches on the benefits of AESA in his latest three videos on AESA planes