Abstract: Helical array antenna is fed from a single-layered radial waveguide to realize the directional radiation of high-power microwave. Low-profile helix is used as a radiation element. The feed wire of each helix is connected with an H-coupled probe, and excited by an outgoing wave in the TEM mode between the two parallel plates of the radial waveguide. Helices and probes are arranged on the upper plate to form a circular array. The excitation amplitude and phase of each element are adjusted by changing the insert length of H-coupled probe and rotating low-profile helix respectively. This antenna accepts directly an azimuthally symmetric output of an HPM source and radiates a high-gain pattern with a boresight peak. H-coupled probes are used to make the array antenna compatible with the intense