Abstract: An antenna for the radiation of ultra-wideband pulsed electromagnetic radiation. The invention is a high gain, transverse electromagnetic parallel-plate, open-sided transmission-line array horn antenna utilizing a binary tree-based design, which produces a multiple number of paralleled horns and final radiation apertures, connected to a single signal feed waveguide. This invention antenna structure produces an equal path length for the signals in each of the paralleled branches, virtually eliminating phase error in the E plane and producing high gain characteristics over most of the desired radiation frequency range.