New line problem of regular expression

could anybody tell me how i can add/append a new line using regular expression in vi on AIX?

i've tried several ways before, but all of them failed. e.g.
:%s/$/\n/
:%s/^/\v\r/

:frowning:

:%s/$/^J/

You'll get the ^J by pressing CTRL+v (to tell vi a special char is following) and then hitting enter.