The GetRadWindow() function is used only when RadWindow displays a content page - i.e. the content page is displayed in an IFRAME. In your case, you are using RadWindow as a content template, i.e. the content is on the same page and that is why oWindow will always return null. If you want to close the window in such case, you only need to get a reference to it by using $find() and then call its close() method.
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