Sardinia

Which international airport in Sardinia? There are 3, in order of traffic
CAG or Cagliari Elmas in the South
OLB or Olbia Costa Smeralda in the Northeast
AHO or Alghero in the northwest

Go to the Wikipedia article of the airport you want to fly to, depending on which part of the huge island you are visiting, then see which airlines fly to Rome (either FIUMICINO or Ciampino). AHO is primarily a RyanAir kingdom.

Alitalia and Ryan Air fly to Càgliari. Air Italy flies to Olbia. Blue Air flies to Alghero. All originate at FCO except Ryan which departs Ciampino. All of these are short, direct flights. Alitalia has almost a flight every hour going to Càgliari.

RyanAir no longer services Alghero from Rome.