Calculation Of The Capacitance Of Leaky Coaxial Cable

Leaky coaxial cable has a good ability of waves cover. When used in undergroundcommunication, it plays an important role in the security of the mine; When used innational defense, it has features of good concealment, not easily being stricken, stronganti-interference ability, great transmission power and so on. When used in the closedarea of metro, tunnel, and high speed railway, it can improve communication quality,reduce traffic accident, and also provide traffic control with powerful communicationtechnical assurance. Hence, we can see that leaky coaxial cable has a promisingprospect. In order to know well about its characteristics, improving its communicationperformance, expanding its frequency range. Owing to the specialty of wide coverage，Leaky Coaxial Cable is widely used in mobile communication in confined areas such asmines，subways，tunnels and buildings，and the research on its key characteristics isbecoming a hotspot increasingly.Beginning the basic theory of Leaky Coaxial Cable, the paper introduced itsstructure, classification and several important performance indexes including operationfrequency-band, coupling loss, transmission loss, resonance characteristics,characteristic impedance, and capacitance. According to the comparison of severalnumerical methods for Computational Electromagnetic, the paper selected the finitedifference method for calculation.The capacitance of the Leaky Coaxial Cable (LCX) with eight-shaped slot iscalculated by Three-Dimentional Finite Difference Method in this paper. Thedifferential equation of electrical potential in the Closed segment and Slotted segment ofthe LCX is derived from Laplace equation. The boundary conditions between interfacesand their discrete forms are given. The expressions for electrical potential andcapacitance are obtained. Then, the accuracy of this method is disscussed. Bycomparing with measured value of LCX with Specifications, the procedure presented isvalidated. Finally, the influence of slot angle on the capacitance of the LCX is analyzed.