In an intrusion detection system of the kind which comprises a "leaky cable" or open transmission line and is used to determine the presence of objects, things or people moving in the vicinity of the leaky cable, a transmitting antenna and a receiving antenna, one of which is an open transmission line/leaky...http://www.google.com.hk/patents/US6252507?utm_source=gb-gplus-share專利 US6252507 - Intrusion detection system using quiet signal band detection
