how are UAV systems (aircraft+ground facilities) fitted with landing aid system?
Each project will have its own specifications. Military UAVs will have different use cases from civilian ones, and, as the comments mention, unmanned does not mean unpiloted.

Most of current UAVs are remotely piloted, meaning that there is a front facing camera relaying images to the ground, where a pilot will command flight adjustments to the vehicle to keep it aligned, no special equipment involved (except for the air-ground communication apparatus). The aircraft will be equipped with the usual inertial sensor unit(s) and GNSS receiver(s).

For situations where you might have an unpiloted aircraft (that are extremely rare today), it is still solvable by simple INS + GNSS, with the additional requirement that you will have to accurately measure the position of the runway in the GNSS reference system (published charts are not precise enough, as they are created for eye-bearing humans, that can correct the course by sight). This is the method we used and we landed 2 meters from the centerline (the two pilots where there for safety, being it the first attempt).
Other projects might include ground-based aid signals akin to an ILS system.