For achieving site calibration of VFTO measurements of GIS

a kind of feed structure is required to conduct the VFTO signals onto the real GIS pipelines. Considering high voltage and wideband characteristics of VFTO

a kind of coaxial transmission line structure using impedance transformation for wide-band impedance matching is designed. Based on the tapered transmission line

the performance of exponential gradation

triangular gradation and Klopfenstein impedance gradation in wide-band impedance matching is studied and the impedance transformation model for real GIS pipeline structure size is designed. The scattering coefficient matrixes of three models are obtained by the full-wave simulation software

and the influence of the structure length and the ripple coefficient on the reflection coefficient of the model is quantitatively analyzed.