Photon cannon

The Photon Cannon is an automated defense structure of Protoss design. Although the Protoss revel in the glory of personal combat, they also recognize the need for automated defenses. As such, the cannon fires an encapsulated antimatter sphere similar to that generated by the Dragoon, which can target air and ground targets. They are enhanced with special sensor technology borrowed from the Observer. Photon Cannons require a link to the Psionic Matrix generated by Pylons.

Weaknesses

 * The Battlecruiser can use the Yamato Cannon to destroy it at a safe distance as well as other long range units such as Guardians.
 * Large numbers of units like Zerglings or Marines can take the cannon out, as it isn't very efficient against multiple foes.
 * High damage foes, like Archons or Ultralisks, can deal large amounts of damage faster than the cannon can.
 * Without Pylons the Protoss have no automated defenses.
 * As with all Protoss units and buildings, EMP blasts from Science Vessels can render them without shields.

Upgrades

 * Plasma Shields

StarCraft II
The Photon Cannon was replaced by the Phase Cannon. It has since returned.

Upgrades

 * Plasma Shields