Why popup in wpf is indepentate from parent window ? As if i pressed alt+tab then still popup window is stay opened.

I have a popup window on my  window ( i used popup because i need to see on the top of my window) when i pressed alt +tab then my window is deactivated but still popup control is not. i need to do explicitly using deactivate event of windows. 

How do i can do without these event ?

Or is there any other control in wpf instead of powerpoint that can be used instead of popup ? In my code i need to set isopen property of popup to show or hide..