Covenant portable shield

Did you mean the Halo 3 Covenant equipment, the deployable cover?

The Stationary Shield Generator as seen in Halo: Reach.

A stationary shield generator^[1] is a device used by the Covenant during offensive ground operations.^[2] These shields are larger versions of the point defense gauntlets used by Kig-yar and some Sangheili. They are created by three small portable generators that are attached together and, when activated, generate an ovoid-shaped shield to provide extra protection for the Covenant troops. These are normally placed at strategic locations, like doors or building entrances, when the Covenant are guarding a small, temporary position. They can deflect all projectiles except rockets, explosions, or large amounts of plasma fire. If one fires at a shield with a projectile weapon, the shots may bounce back and do actual harm to them. This can be graphically demonstrated with a high-caliber weapon such as a sniper rifle. Only plasma-based weapons are able to temporarily overload the shield's generator. The human counterpart for the stationary shield is the combat barrier.

In Halo: Combat Evolved if one of these shields is hit by a vehicle, it will be permanently disabled. In Halo 2, vehicles cannot collapse them on impact. In Halo 3 it reappears or was remade as a piece of Equipment, the Deployable Cover, where it can be deployed by troops.

In the Halo: Reach level Nightfall, a bank of stationary shield generators are set up on the far side of the bridge opposite the Covenant stealth pylon.^[3]

Deployable cover

Main article: Deployable cover

The deployable cover replaced the stationary shield generator in Halo 3. It is portable and curved rather than flat, and is destructible and much weaker from the other games.

Trivia

The shield generated by a stationary shield generator is 2.49 meters, or 8.17 feet, high.
The AI won't see past shield generators since it acts as a solid, opaque object to the AI.
If a player has a Shotgun, or other long barreled weapon, and they walk right up against a stationary shield, the barrel goes through the shield and one can shoot through it at opposing enemies. Similarly, it is possible to snipe enemies while never having to expose oneself and take cover again. The length of the weapon which is exposed should be disregarded, since the shot from most weapons come from the camera.
In Halo 2 on the level Delta Halo, one can use the stationary shield generators placed at the entrance to one of the Covenant-held temple complexes to propel their vehicle away at a high speed by first disabling the shields, placing the vehicle on the generator and waiting until the device activates. This can also happen in Halo: Combat Evolved, though if the player is in a human vehicle, it is likely to fall out and die from fall damage.
In Halo 2, if one whacks a Grunt body into a stationary shield generator with the Sputnik Skull on, the body will hit the shield generator hard enough to disable it.
In Halo 2 if one stands on top of a deployed generator and shoots it with a Plasma Rifle, the generator will overload and you will be floating on top of an invisible shield.

Gallery

A stationary shield generator in Halo: Combat Evolved.
The Master Chief passing through one of many areas which the Covenant have set up shields.
The three stages of a stationary shield generator, as seen in Halo 2. When shot at, the shield generator overloads and temporarily deactivates. A few seconds later it reactivates, returning to the initial stage.
The three stages of a stationary shield generator, as seen in Halo: Reach.
A bank of stationary shield generators in the Halo: Reach level Nightfall, on the side of the bridge opposite the Covenant stealth pylon.