Abstract: A dual leaky coaxial cable comprising a pair of parallel elongated conductors, a dielectric surrounding each of the conductors, separate first external conductive shield apparatus surrounding at least the major portion of each of the dielectrics, separate second external shield apparatus surrounding each of the first external shield apparatus, apparatus associated with the shield apparatus for selectively coupling magnetic fields which may surround each of the elongated conductors through the first and second surrounding external shield apparatus, and apparatus for maintaining the individual respective second external shield apparatus separated by a distance which is a fraction of the diameter of either of the second external shield apparatus.

Abstract: A continuous wave (CW) leaky cable sensor for an intrusion detector uses a pair of elongated parallel cables, one for establishing an RF field and the other for receiving the field. A modulator is connected at an intermediate location of the receiving (or transmitting) cable, subdividing a detection zone into detection regions on each side of the modulator. The modulator selectively modifies a signal received by a portion of the receiving cable connected to its input. By processing the signal at the output of the receiving cable, the detection region for either side of the modulator in which an intrusion has occurred can be determined. The resolution of a CW sensor is thus increased at low cost. Multiple modulators can be used at spaced locations increasing the number of detection regions, and thus the resolution.

Abstract: A leaky cable useful antenna or as an intruder detector sensor either buried in a single trench or above ground substantially reducing sensitivity variations due to the environment. Egression of the electric field from the cable is blocked but magnetic fields escape. The velocity of the externally propagating electromagnetic field is slowed and attenuated. In one embodiment, the leaky coaxial cable is comprised of an inner conductor, a dielectric surrounding the inner conductor, a first external shield having low series impedance at VHF frequencies surrounding the dielectric, means for coupling a magnetic field through the first external shield, a second external shield surrounding the first external shield having high series impedance relative to series impedance of the first external shield and means for limiting VHF conduction current between the shields, which effectively causes separation of the internal and external propagation fields of the cables.