AAD system in this discussion means the short range self propelled SP systems which can keep up with armor formations and engage targets which are hostile to the armor formations.
This below system is a good example:
Type 95 SPAAA - Wikipedia, the free encyclopedia
And then something based on this:
Pantsir-S1 - Wikipedia, the free encyclopedia
A system which can engage targets right above the armor formations and with a missile system of 20-25KM range which can target far away targets which may be engaging the armor formations from 5-8 or 10KM away.
SP guns can be a few hundred feet behind the armor formations thus safe from direct enemy fire but able to engage targets close to or above the armor formations.
And the SP missile system can be 2-3KM behind the armor formations and able to engage targets 18-23KM infront of the armor formations.
And this AAD setup is much cheaper and affordable as well as deadly,provided the system is effective and tactics well evolved.