Dual Ridged Horns have been analyzed recently in . The work showed the problems with the integrity of the main lobe of the pattern that these types of horns have. While the work on improving these horns has been concentrated primarily on the 1 to 18 GHz  models DRHA also cover other frequency ranges. The 200MHz to 2GHz range DRHA are the required antenna in the Mil Std 461E for both emissions and Immunity in the 200MHz to 1GHz range.
It is of interest the sudden drop in gain at the upper end of the frequency range. The Gain drops from a 9dB average to 3.5dB between 1900 and 2000MHz. This is similar to the drop in gain seen in the 1 to 18GHz models between 16 and 18GHz. To get a better idea of what is causing the drop in gain a 200MHz to 2GHz DRHA was placed in an antenna pattern measurement taper chamber.