A Time-Domain Numerical Method for Multi-Conductor Coaxial Lines Using the Exact Retarded Potential Integral Equations

We present a time-domain numerical method for calculating the current propagating through coaxial lines including the radiation effect. In previous studies of transmission lines using the retarded potential integral equations (RPIE), the so-called thin-wire approximation to the RPIE has been mainly used. However, the thin-wire approximation has the problem that the unphysical oscillation occurs when the spatial mesh size is smaller than the radius, even for one-conductor line. In addition, the application of the thin-wire approximation in multi-conductor coaxial lines causes a problem in the formulation. We solve these problems by developing a numerical method using the exact RPIE. We perform numerical calculations in the time-domain for two-conductor coaxial lines and obtain numerical solutions even for the very small common-mode current that causes radiation emission.