To produce broadband electromagnetic pulse(EMP)radiation,we design and test a sub-ns pulse system which is utilized to drive an axial mode helix antenna.This sub-ns pulse system consists of a 10-stage Marx generator,an intermediate storage capacitor,an impedance transforming line,and can generate a high voltage of 570kV with a rise time of 1-1.5ns on a 300-Ω-resistance load.The diameter,pitch and tus of the helix antenna are 29 cm,19.5cm and 5,respectively,with a design frequency of 300 MHz.When the charging voltage of the Marx generator is 30kV,the electric field of radiated EMP measured 3m from the source is 35kV/m with a central frequency of 250MHz.The relatively spectral bandwidth is 25%.The radiated EMP results are reproducible and the system will work in repetition mode if the available do power is utilized.