Get the Window Owner for OpenFileDialog

[soonhui]

I have the following code at my plugin class ( the one that inherits from IExtensionApplication):

 SaveFileDialog saveDialog = new SaveFileDialog();
       
            if (saveDialog.ShowDialog(/*System.Windows.Window winObj */) == true)
            {
                serializer.Write(proj, saveDialog.FileName);
            }

In the ShowDialog, I can pass in the owner of the SaveFileDialog,  so I want to pass in the AutoCAD Main Window as the owner. 

How to do get the AutoCAD Main Window ?