This article details how to filter and group by week within Report Design.
Method
To filter and group by week you must use the Factset More Fields Date instead of the Period Dimension. The Period Dimension has a FY Week but it is aggregated to the first week of the Fiscal Period.
Go to the Factset and More fields and you will see a Date Dimension.
You will see a Field called FY Week which you can use by Grouping by Week.
You can also use the WeekStart function with a Date Parameter. You can drag and drop your Date into a filter and then go into Parameters to select the correct Date view for use with a Function.
You can then use the Weekstart function with a Date Parameter.
‘{Date.WeekStart.SqlDate}’:{@Date}
Date is the name of the Parameter and is in the front which establishes the Sunday of the week to the Parameter.