Our system indicates that you have opened a support ticket concerning the same issue. In order to avoid duplicate posts, I suggest that we continue the communication in the support ticket.
However, I post my reply here, as it might be useful for other members of the community:
In order to implement the desired functionality, I recommend that you get the expression tree built by the RadFilter control, apply it to the datasource and then set the filtered datasource as datasource of the desired control.
I hope this helps.
the Telerik team