Foreign names are usually written by approximating the sounds phonetically with Katakana. I am not totally sure how your name is pronounced in Portuguese, but I think in Japanese your name might look like this:
テーナ・カミラ
Or if the "Th" has more of a lisp to it, then it could be this:
セーナ・カミラ
The "Th" sound doesn't really exist in Japanese though, so it is difficult to approximate it.