- Level 2-3 Air Attack and Plating
The Fleet Beacon is a Protoss technology building at the very end of its tech tree. The Fleet Beacon opens up several aerial upgrades as well as allowing the Protoss player to construct Carriers. It also unlocks second and third levels or air weapons and air armor upgrades at the Cybernetics Core. It requires a Stargate to be built.
The Fleet Beacon does not build any units directly. The structure's Plasma Shields can be upgraded at the Forge. The Fleet Beacon is powered by the Pylon, but if this Pylon is destroyed, the Stargate would still be able to produce Carriers.
The upgrades available at the Fleet Beacon are not commonly researched in any of the Protoss match-ups, as they are quite specialized and thus directed towards a specific late game strategy, as opposed to a more universally useful upgrade such as the Zealot Leg Enhancement. The upgrades available focus on the three primary air units: a Carrier upgrade that doubles the Interceptor capacity, two Scout upgrades that enhance its sight range and speed, and two Corsair upgrades that enhance its Disruption Web ability.
In PvT match-ups, if the Fleet Beacon is built by the Protoss player, it would generally occur during the late game as part of a Carrier force. A Terran Comsat Scan that detects the Fleet Beacon will generally suspect Carrier production. In this scenario, the Carrier Capacity increase is generally the most researched upgrade at the Fleet Beacon. In some strategies, the Protoss player will opt for a Disruption Web tactic against ground units and defensive structures, in which case the Fleet Beacon is built for that purpose.
In PvP and PvZ match-ups, the Fleet Beacon is also not a commonly built structure. On rare occasion, the Protoss player may build the Fleet Beacon to produce Carriers or Disruption Web-enabled Corsairs against the Zerg or Protoss opponent's ground units and defensive structures. It is also occasionally used in PvZ when the Zerg to further upgrade Corsair weapons when the Zerg is going air heavy.