Abstract: An intrusion detection system of the type using cables arranged along a perimeter to be protected and sensing changes in the electrical field around the cables caused by the presence of an intruder. The cables are divided into sections or blocks and typically only one of the sections is energized at any time. The variations caused by an intruder at the selected sections are transmitted through the intervening section to the receiver portion of a transceiver located at one end of the cables. This indicates in which section intrusion has occurred. The system uses continuous wave excitation whereby the expense and complexity of high speed switching and timing of r.f. signals are avoided.

Abstract: An intrusion detection system using waves guided by the conductive outer sheath of a coaxial cable. An r.f. signal from a transmitter is supplied between the inner conductor and outer conductor or shield in conventional fashion. Coupled wave devices are spaced along the cable; each coupled wave device transferring r.f. energy between a transmission mode within the cable and a guided mode propagated along the exterior of the conductive outer shield. In one embodiment a second coaxial cable similarly provided with coupled wave devices is spaced from the transmitter cable and has one end connected to a receiver. The change in r.f. coupling between the cables caused by an intruder produces variations in the r.f. energy coupled to the second cable which is detected at the receiver. Alternative embodiments include the use of a single cable with coupled wave devices adapted for both transmission and reception.

Abstract: A leaky coaxial cable is designed to produce a defined coupling between its interior and exterior. A bonded and insulated outer conductor of relatively large width relative to the cable diameter, is spirally wound at a low pitch angle to provide at high frequencies a coupling level having minimal effect on the coaxial properties of the cable.

Abstract: A simulated target for use in conjunction with detection systems using coupled transmission lines. The simulated target is positioned in the vicinity of the transmission line and the response used both to monitor system operation and to calibrate system response levels. The simulated target can be of a type having its electrical length variable under system control or can be purely passive serving to alter the stationary response profile of the system.