To understand the influence of VFTO on secondary equipment of GIS

oscillatory bounded-wave simulator is used to simulate the VFTO radiation field.The simulator has a typical structure of plate transmission line.Continuous characteristic impedance must be ensured in the wave propagation path to prevent the refraction and reflection of wave.Therefore

it is necessary to analyze the characteristic impedance.In this paper

the reflection coefficient method is adopted to calculate the characteristic impedance of the electromagnetic field forming device.A simulation model of the oscillatory bounded-wave simulator is established with the software CST.Applying a step signal to the simulation model

and recording the electric field waveform at the center of the work space

the amplitudes of the incident wave and reflected wave are obtained.According to the relationship between the reflection coefficient and the characteristic impedance

the value of characteristic impedance is calculated.Subsequently

the influences of the structural factors on the impedance are analyzed.The result shows that the reflection coefficient method is highly accurate and easy to be used

and the length of the transition section and the size of both ends of the electromagnetic field forming device affect the magnitude of the characteristic impedance.The longer the transition section or the smaller the size of both ends

the better the impedance consistency in the wave propagation path.