A new radial-line helical array (RLHA) using dual-branch helical antennas has been designed for improving the power capacity of RLHAs. The helical element is cavity-backed to lower the mutual coupling and its power capacity is higher than the conventional ones. The components of the proposed array are discussed and the power capacity is obtained by simulation. Compared with the typical RLHAs, the proposed sub-array has not only higher power capacity but also uses fewer elements. Experimentally, the measured results of an array prototype indicate that high gain as well as circular polarization has been successfully achieved.