Leaky Coaxial Cable Intrusion Sensor Using Directional Coupler
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Solution Overview
Problem
Current leaky coaxial cable sensors are limited by sensitivity variations along the cable length due to soil properties and installation parameters, leading to false alarms and missed detections, and require separate transmit and receive cables, which increases installation costs and complexity.
Innovation Solution
A cable-guided intrusion detection system that uses a single leaky coaxial cable for both transmission and reception, with a directional coupler to separate signals, and employs simultaneous polling of all range bins for enhanced performance, and zero mean pseudo-random complementary codes to reduce interference and allow DC power usage without compromising performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate transmit and receive cables are used, then detection reliability is improved, but installation cost and complexity increase
Solution Approach 1:
The patent combines transmit and receive functions into a single leaky coaxial cable by using directional coupling. The cable serves dual purposes: transmitting the RF signal and receiving the reflected signal from intruders. This is achieved through a directional coupler that separates the transmitted and received signals, eliminating the need for separate cables while maintaining detection reliability.
Solution Approach 2:
The single leaky coaxial cable performs multiple functions: it acts as both the transmit antenna and the receive sensor. The cable radiates the RF signal outward and simultaneously captures the reflected signal from intruders. This multi-functionality reduces the number of components needed and simplifies installation while preserving detection capabilities.
2Measurement precision
If cable grading is implemented to compensate for sensitivity variations, then detection precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the operational parameters of the system by using coded pulse transmissions and digital signal processing with correlation techniques. Instead of modifying the cable's physical structure through grading, the system uses signal processing to compensate for sensitivity variations along the cable length. The coded pulses and correlation processing enable precise intruder location and detection without requiring graded cables.
Solution Approach 2:
The patent replaces the mechanical/physical solution of cable grading with an electronic/software-based solution. Digital signal processing and correlation techniques are used to compensate for sensitivity variations, replacing the need for physically graded cables. This substitution reduces manufacturing complexity and cost while maintaining or improving detection precision.
3Measurement precision
If FM-CW with FFT processing is used, then intruder location capability is improved, but side lobe interference increases causing false alarms
Solution Approach 1:
The patent uses periodic coded pulse transmissions instead of continuous FM-CW signals. By transmitting coded pulses at regular intervals and using correlation processing, the system achieves intruder location capability while avoiding the side lobe interference problems of FFT-based FM-CW processing. The periodic coded transmissions provide clear temporal signatures that improve reliability.
Solution Approach 2:
The patent uses correlation processing that compares the received signal with a copy of the transmitted coded pulse. This correlation technique provides sharp peaks for intruder detection with minimal side lobe interference, improving both location capability and reliability. The copied reference signal enables precise matching and detection without the artifacts of FFT processing.
4Device complexity
If sequential polling of range bins is used, then processing simplicity is maintained, but update rate decreases
Solution Approach 1:
The patent uses periodic coded pulse transmissions that illuminate all range bins simultaneously. Each coded pulse transmission provides information about the entire cable length, and correlation processing extracts intruder locations from all range bins in parallel. This approach maintains processing simplicity while achieving high update rates by utilizing every transmitted pulse for comprehensive monitoring.
Solution Approach 2:
The patent performs preliminary correlation processing on the received signals to extract intruder information before final detection and display. By pre-processing the signals from all range bins simultaneously through correlation with the coded pulse, the system prepares the data for rapid update without increasing overall system complexity. This preliminary action enables high update rates while maintaining simple processing architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces installation costs, enhances detection precision and reliability, and allows for simultaneous detection of multiple intrusions with improved signal-to-noise ratio and dynamic range, while minimizing the effects of environmental factors like wind and thermal expansion.
Implementation Method 1
transmitting a phase modulated coded pulse down the cable creates an electromagnetic field extending into the surrounding medium
Implementation Method 2
The external energy reflects off a target moving in proximity to the cable and some of the reflected energy couples into a receive coaxial cable
Data Source
AI summary
The present invention provides an intrusion detecting system and method for precisely locating an intruder along the length of a sensor cable and for determining the intruder distance from the cable to precisely locate multiple, simultaneously occurring intrusions. The method includes the steps of: generating a TX signal and transmitting same over a first transmission line of the sensor cable, for creating an electromagnetic field; detecting an RX signal induced in a second transmission line of the cable by the electromagnetic field and identifying in the RX signal a contra-directional reflection received from a target and a co-directional reflection received from the far-end of the first transmission line, processing the contra-directional reflection for providing a first coordinate of the target, and processing the co-directional reflection for providing a second coordinate of the target. The method and system may also be implemented with a “true one cable” using a single coaxial cable sensor with a directional coupler for separating coupled signals along a single transmission line in the cable. Ultra high speed data correlation of the RX signal is achieved through use of a field programmable gate array. The present invention also provides a separate calibrated threshold for every meter of cable to reduce the installation cost associated with meticulous control and the number of cables required for sites with varying burial mediums. In another embodiment, the use of two parallel single cables may be utilized whereby each cable in the system is used to detect and locate intruders independently and more clearly define the direction of crossing and the speed of crossing.