I. Introduction
Antennas offering ultra-wideband (UWB) radiation characteristics have been the subject of much research in recent years. Various antennas covering UWB have been studied in the literature including travelling-wave antennas, such as Vivaldi antennas; frequency-independent antennas, such as biconical antennas; self-complementary antennas, such as logarithmic spiral antennas; and multiple resonance antennas, such as fractal antennas. Among these, printed planar antennas have received much attention due to their planar structure, making them easily mountable on planar surfaces, and simple low-cost manufacturing. Bow-tie antennas, which are the planar version of biconical antennas, have the advantage of being considerably compact in size and offering good time domain and broad-band frequency domain radiation characteristics [1], [2]. UWB bow-tie geometries studied in the literature can be given as slot [3], [4], double-sided [5], self-complementary [6] and self-grounded [7].