Contents I. Introduction
The shell of a ship is generally used as the ground plane for electric and electronic equipment aboard. As a result of the limited conductivity of the shell conductor, some ground impedance is formed in the ground loop. Different devices are likely to cause electromagnetic interference because of the ground impedance coupling. To analyze and study the regularity of interference, it is necessary to know how impedance varies with frequency. The ground impedance is generally divided into two parts: one is caused by the internal impedance in the conductor with a limited conductivity and the external inductance as well as other factors with the conductor itself; the other part comes from the distributed inductance and capacitance, which are caused by the coupling between the ground plane and the external devices. As far as the isolated flat conductor is concerned, this paper mainly discusses the regular variation of the conductor impedance with the frequency and the conductor configuration as a result of the AC skin effect of the finite conductivity and the striction effect of the current contact points confinement.