Abstract: The invention relates to a leaky cable intrusion detection system comprising a pair of spaced, parallel, buried, leaky coaxical cables. A radio frequency signal is applied to one of the cables, whereby an electromagnetic field outside said one cable is established, and a radio frequency signal from the field penetrates and is received from the other of the cables whereby disturbances in said field can be detected. The cables are spaced apart a distance such that they are intermediately coupled, being coupled to a greater degree than loosely coupled and to a laser degree than tightly coupled. In the preferred embodiment a longitudinal shield is spaced from and is below the cables. By varying the spacing between the cables and the shield, variations in field shape and sensitivity of the system can be substantially reduced.

Abstract: A graded leaky coaxial cable comprised of a center conductor, a dielectric surrounding the center conductor, and a braided conductive shield woven around and surrounding the dielectric. The shield has progressively fewer ends along its length, whereby progressively larger non-conducting gaps are formed separated by closely woven groups of carriers, thus facilitating controlled penetration of a radial frequency field through the shield.

Abstract: A sensor for use in a leaky cable intrusion system which is comprised of a pair of parallel buried coaxial cables, each of which has a velocity of propagation factor different from the other. This results in different sensitivity characteristics with length, resulting in a combined sensitivity which has markedly reduced amplitude variation over cables having similar velocities of propagation. It also makes feasible a system having ungraded cables in which the position of intrusion in the field set up by the sensor can be determined.

Abstract: A method of producing a leakage graded coaxial cable having a braided shield, in which ends of the shield wire are dropped as braiding progresses. Gaps in the shield having progressively increasing size are produced through which the radio frequency field leakage occurs, which facilitates providing a constant radio frequency field around the cable. The cable is coated with a jell flooding agent prior to extrusion of its protection jacket, which fills the interstices and gaps of the shield, and solidifies to a waxy, semi-resilient consistency. The resulting cable can be coiled and flexed, maintaining its shield reliability, and rejects water and fluids in case pinholes in the jacket occur.