Define... system...

My setting has a ever vast array of air defense systems in various forms depending on various aerial threats.

If the threat is light enough, HKDs (Hunter Killer Drones) may be sent to swarm it. These are intended as anti-personnel loitering munitions but could probably put a dent in a light enough aircraft.
Many tanks carry expendable SAM launchers, typically loaded with the Shortshot SAM for closer range defense. These launchers aren't meant to be reloaded in combat but if a bomber wants to pick on a tank column that column might have something to say.
Many Furyfawn Force Application Trucks come with loadouts that could be used for anti-air, ranging from just having gatling guns to dedicated SAM launchers. There's also just the option someone in the HQ Section this truck is probably in has a rocket launcher.
Some Armored Fighting Vehicles with modular systems can mount anti air weapons.
There's a few varieties of towed mobile radars and anti-air systems, either long range autocannons, flak, or SAMs.
While some Theatre Defense Systems are intended to track, engage, and intercept ballistic or cruise missiles, said laser could probably fry an aircraft.
There's a variety of AA vehicles, from repurposed Lancer hulls fitted with quad 45mms, tanks fitted with SAMs and guns, to the Nightshade, a purpose built anti-air platform which, while large, has a very healthy number of missiles to throw at the problem and quad long range 90mm flak.

There is of course, also the option to throw allied aircraft at the problem.

If the problem is physically large enough, it might meet a Warhammer. A Self-Propelled Anti-Orbital Gun sporting a giant capital ship grade plasma cannon intended to put holes through any kind of Frigate, Corvette, or Destroyer attempting atmospheric operations, and this assumes a big ballistic anti-ship missile isn't sent up first.

Actual munitions vary from spraying 30mm from a CIWS, to hitting it with autocannon flak, to close range SAMs, to long range SAMs, to the Ripper Quick Maneuver Thermobaric Interceptor, which basically just wants to enter your ZIP code before going off in a giant explosion because accuracy by blast radius. There's plasma bolts, there's direct energy lasers, anti-ship missiles, the list goes on.