Covenant portable shield
From Halopedia, the Halo wiki
A Stationary Shield Generator is a device used by the Covenant during offensive ground operations. These shields are larger versions of the Jackal Personal Arm Shield. They are created by three small portable generators that are attached together and, when activated, provide extra protection for Covenant troops. These are normally placed at strategic locations, like doors or building entrances, when the Covenant are guarding a small, temporary position. This information is derived from first-hand accounts, though it is unknown how the energy fields are generated. They can deflect all projectiles except rockets, but an explosion, impact with a vehicle, or large amounts of plasma fire can temprorarily collapse them.
Trivia
You can not be seen by the Covenant behind one of these shields.
If you fire at a shield with a human weapon, the shots may bounce back and harm/kill you!
If you have a shotgun and you walk right up against it the barrel goes through, and you can shoot through it.
