Is it necessary to have a parda(for eg:a curtain) between a man and a woman while offering namaz? No matter even if it's a mehram, I know that a woman needs to stand behind a man while offering namaz, but is it mandatory to have any kind of parda in between?

If they are married couple or mahram then there is no need for parda, as long as the place where the woman is doing Sajdah is by the knees of the man or behind, then it is fine