A broadband stacked multi-spiral antenna array comprising two or more spiral antennas with a dielectric layer having a generally uniform thickness positioned between each pair of stacked antennas, which are all center-fed and in-phase. The antenna array may be embedded in a non-conductive material, such as fiberglass embedded in a resin, a honeycomb core sandwich, or structural foam, that may be used to form a structural element of a mobile platform. The structural element may include a via providing a pathway for coaxial cables. If two structural elements are hatch covers on the port and the starboard sides of an aircraft, the use of a stacked multi-spiral antenna array in each structural element provides two roughly hemispherical coverage patterns which together provide an omni-directional coverage pattern. The stacked multi-spiral antenna array may also include a reflecting cavity placed at the bottom of one of the spiral antennas.