French to English Science Telecom(munications)

The context for the term is the following: "On distingue le champ proche et le champ éloigné d'une source. Pour les petites antennes, la zone limite entre ces deux champs se situe à la distance dúne demi longeur d'onde environ; pour les grands pylônes, cette distance est plus grande."
It is found in an article about the safety of mobile telephones which is being translated into British English.
I have found a couple of possible translations - boundary zone, fringe area - however i am unsure if either of these would be correct in this context