Abstract: A leaky coaxial cable for use as a sensor in a buried or other medium, which has a conductor located parallel to, and in proximity with the shield along the cable, but insulated therefrom. Preferably the two wire transmission line formed by the external conductor and the shield is terminated with an impedance matching the characteristic impedance of the transmission line (for minimum reflections). The external conductor can be oriented to cause the field in a given direction (e.g. above the surface of the burial medium) to be compensated for field variations caused by variations in the burial medium.

Abstract: This invention is an intrusion detector which uses codirectionally coupled CW leakly cable sensor techniques. Successive sensors are connected serially through R.F. decouplers, and each is polled and is sent power from a control unit via the serial cables, through the decouplers. The detector thus provides both intrusion detection and a secure data link.