I am new to AI. I have saved my file in DWG, but the person I am sending it to says it opens in raster and has a double line. I am creating patent drawings, so there should be only one line. I am sending the file to someone who uses old-school CAD, like 1999 CAD.
From the Illustrator Export menu under File -> Export choose "AutoCAD Interchange File (*.DXF)"
After clicking export in the file dialog that opens, you can choose the version of cad to export for. Since you mentioned the person handling the file might be using old software you should most likely choose R14/LT98/LT97