Intrusion detection system using leaky transmission lines
First Claim
1. An intrusion detection system comprising an antenna located within the perimeter of an area to be protectd, a leaky transmission line extending around the perimeter so that the presence of an intruder alters the electromagnetic coupling between the antenna and transmission line, an RF transmitter coupled to one of the antenna and transmission line and a receiver coupled to the other, means detecting incremental changes in the in-phase and quadrature components of signals received at said receiver and means separately measuring and accumulating magnitude and phase angle of said incremental changes to track and indicate the presence of an intruder.
3 Assignments
0 Petitions
Accused Products
Abstract
A sensitive intrusion detection system has an RF excited antenna located within the area to be protected and a leaky coaxial cable extending around the perimeter. The presence of an intruder alters the coupling between the antenna and the coaxial cable thereby changing the signal received by the cable. The detection system is responsive to incremental changes in the in-phase and quadrature components of the received signal. When these components are plotted against each other a cardioid-like curve is obtained in the ΔI,ΔQ plane. By tracking both magnitude and angle of this curve as it is generated a sensitive detection mechanism is provided. When the variations in magnitude and angle exceed a threshold an alarm is sounded. To avoid the possibility of intruders using a particular path would gives a null angle response, a second cable adjacent to the first may also be employed. A further embodiment illustrates the use of three cables together with a separate antenna which provides multiple independent sensing systems.
30 Citations
17 Claims
- 1. An intrusion detection system comprising an antenna located within the perimeter of an area to be protectd, a leaky transmission line extending around the perimeter so that the presence of an intruder alters the electromagnetic coupling between the antenna and transmission line, an RF transmitter coupled to one of the antenna and transmission line and a receiver coupled to the other, means detecting incremental changes in the in-phase and quadrature components of signals received at said receiver and means separately measuring and accumulating magnitude and phase angle of said incremental changes to track and indicate the presence of an intruder.
-
17. An intrusion detection system for a site where an intruder is constrained to follow a fixed path, comprising a pair of leaky transmission lines along said path, an RF transmitter coupled to one of the lines and a receiver to the other means detecting incremental changes in the in-phase and quadrature components of signals received at said receiver and providing Δ
- I and Δ
Q signals representing said incremental changes, means producing signals indicative of the area and phase angle swept out by these components in the Δ
I,Δ
Q plane and means indicating the presence of an intruder when both area and phase angle exceed preset amounts.
- I and Δ
Specification