An Anti-Replicator Field is one of several adaptions of the Atlantis' shield developed by the Atlantis expedition. By combining the crystal of an Anti-Replicator gun with the shield emitter of Atlantis, the emitters would emit a city-wide Anti-Replicator Field the moment the shield is activated, destroying any Replicator inside the city. However for this system to work, all ten shield emitters must be outfitted with the crystals.
This system also works on a small scale on a Puddle Jumper's. By interfacing the ARG crystals with the cloak of a Jumper and expanding it, a large Anti-Replicator field would be created, destroying any Replicator who would pass through it.
An Anti-Replicator Field was used the first time by Lt. Colonel John Sheppard's team, when they tried to free Atlantis after the Asurans had taken over the city. To prevent the Replicators from adapting to the frequency of the weapon, they adapted the shield emitters of Atlantis. To allow this plan to happen they tricked Richard Woolsey into thinking Sheppard and his team would blow up the shield emitters so the Daedalus could destroy Atlantis. When the Asurans probed Woolsey's mind they found out about the plan and allowed the team to complete its mission. The Asurans removed the C-4 but didn't remove the ARG crystals. When the Asurans raised the shield they unwittingly activated the Anti-Replicator Field destroying them all almost at the same time, thus not allowing them to adapt to the field. (SGA: "The Return, Part 2")
Several months later, another Anti-Replicator field was created with the Puddle Jumper while Sheppard's team was on Asuras to steal a Zero Point Module. This field was used to protect Sheppard's team and Dr. Elizabeth Weir from the Asurans, while trying to upload a command into their base code. The field descended down into the rooms beneath the jumper. However, after several attempts, the Asurans managed to adapt to the AR frequency, rendering the field useless. Furthermore, the amount of power drain used to create the field meant the Jumper couldn't cloak, let alone go into hyperspace, if it wasn't for the timely arrival of the Apollo. (SGA: "Lifeline")