In 1991, Katz et al. [173] used the FDTD method to analyze both 2-D and 3-D horn antennas, while a year later, Tirkas and Balanis [169] also analyzed 3-D horn antennas. In 1994, Tirkas and Balanis [174] extended the contour path FDTD method and used it to analyze pyramidal horns with composite inner E-plane walls.