Antenna embodiments are illustrated that are particularly suited for use in aircraft navigation, identification and collision avoidance systems. An exemplary antenna embodiment operates about a center wavelength and in association with a ground plane and comprises first and second grounded, shortened, and top loaded monopoles. These monopoles are spaced apart above a ground plane and each of them includes a feed post, a shorted post, and a top load wherein the shorted post is spaced from the feed post, is coupled to the ground plane, and has a length less than one fourth of the center wavelength. In addition, the top load is coupled to the feed post and the shorted post and is configured along orthogonal minor and major axes of the top load to have a width along the minor axis and a length along the major axis that exceeds the width.