Aiming at the problems of low space utilization

large size and possible damage to the internal electric field distribution of in-built ultra high frequency (UHF) sensor for gas insulated switchgear (GIS)

a new type of flexible built-in spiral antenna is designed in this paper. The antenna proper is miniaturized by using the sine wave loading mode in which the amplitude increases linearly with the argument angle so that the radial size of the antenna is reduced by 57.8%

and the back fed balun is meandering miniaturized so that the balun length is reduced by 56.4%. The designed flexible antenna body has a diameter of 144 mm and a thickness of 0.27 mm. The results of finite element simulation and physical test show that when the bending radius of flexible antenna is 0 mm

250 mm and 350 mm

voltage standing wave ratio (

VSWR

) is ≤ 5 in 720 MHz ~ 3 GHz frequency band; and is ≤ 2 in 1.02 GHz ~ 3 GHz frequency band. It has good omnidirectional radiation characteristics in the working frequency band. The partial discharge test platform is set up to analyze the antenna performance. The results show that the PD radiated electromagnetic wave signal with discharge less than 20 pC can be detected before and after bending deformation.