In order to obtain the attenuation characteristics of EM in GIS with coaxial structure

a simplified model of coaxial GIS is built by using FDTD method to simulate the inferences of the resonant cavity

energy leakage and transmitting antenna on propagation of partial discharge electromagnetic signals. Simulation shows that the end enclosed coaxial structure can be viewed as a coaxial resonant cavity with low quality factor

which would induce more complex EM signal components of higher-order mode. The position of insulator would reduce the components of higher-order modes in EM signal propagation to result in a decay of amplitude in measurement. The protrusion on conductor plays a role of excitation source of EM signals

and facilitates the propagation of the EM waves.