Study On The Interference Mechanism Of Electromagnetic Field Around Intruded Coaxial Cable

The perimeter intruder location detecting system based on leaky coaxial cable is a newly invented outdoor detecting system in recent years. It has some special characteristic such as high conceal property, the low error rate and so on. The system mainly makes use of the electromagnetic radiation field of leaky coaxial cable as a means of detecting an intruder invasion. So, it is necessary to analysis the cylindrical electromagnetic radiation field of the cable when the intrusion occurs. The field analysis is beneficial to the choice of the cable's type, the location of the cable, and can give help to choose the more efficient detection method.The study of electromagnetic radiation field characteristics of a leaky coaxial cables is described in this paper using both the theoretical calculation and computer simulation method.In the theoretical study process,we firstly constructed SLYFRY-75-9 type leaky braided coaxial cable outer conductor model, according to the magnetic field made by infinitely long straight current-carrying wire, we obtained the magnetic field distribution of any diamond hole when the cable outer conductor is a plane by means of superposition method. Further, we get the equation about the magnetic field at any point above the diamond-shaped aperture of the braided coaxial cable when the outer conductor curled into a circular. and calculate it using MATLAB. At last, we discuss the field transmission and radiation of the leaky coaxial cable by using pattern analysis ways.In the computer simulation process, we firstly simulated the electromagnetic radiation field at two situation through finite-difference time-domain method, one is the cable only under air condition ,the other is some media next to he cable. The field characteristics and the performance parameter are obtained and some electric field distribution graphs are given in this essay. All the simulation is finished by using the REMCOM's XFDTD electromagnetic simulation software. Secondly, we provided a dynamic analysis method as a medium moving over leak cable radiation field. Through observing the dynamic movies when the media crossing the cable vertically, We found that the shape of the section of the field is no longer a rule circular, the field near the medium significantly attenuated, The media will block the electromagnetic field and absorb part of electromagnetic energy, thus, The amplitude changes and the phase lag will be definitely caused along electromagnetic wave propagation. These two points can be used as the basis of the received signal gained by detected cable. Finally, this paper describes a number of existing leaky cable radiation detection program, and proposed a new program based on differential detection operations.