210 Analysis of Coupling Interference for Communication Transmission Line

A theory for the problem of electromagnetic field coupling to transmission lines is presented and the important factors which can effect the value of interference, are studied. The port voltage of cable above the ground is changed for the reason of reflected fields, which is effected by the conductivity ,dielectric constant and surface coarseness. The distributed voltage driving the internal conductors of a shielded cable is gotten from the products of shield current and transfer impedance of the shield rather than from incident field was described in the discussion of coupling to cables. Through the numerical calculation, some important coupling characters of external field and transmission lines are elicited. For elevating the exactness of the communication, some important methods are figured out to control electromagnetic interference of transmission lines.