You can control whether ads are allowed to appear multiple times on the same page or whether to limit them to only showing once. This allows you to optimize the experience for the audience to drive maximal engagement - whether you are looking for multiple exposures, or explicitly only a single exposure of an ad. By default, only one ad per advertiser will be served on a page unless your organization opts for a different setting.
To change whether ads appear more than once on a page for a given campaign, following the steps below.
Identify the campaign in the Campaigns list or the Campaign Detail page
Click "Edit Campaign"
Click on the "Advanced" tab
Select / Deselect "Allow Ads to run on multiple placements on a publisher page at the same time".