“…Therefore, in order to meet the requirements, many researchers provide a large number of solutions. These solutions mainly include: a) ultra-wideband omni-directional antenna, of which wafer monopole antenna [1,2] is the representative, and various special-shaped-pole antennas [3][4][5], which are mainly used in the frequency band from 3.1 to 10.6 GHz (approved by FCC), but generally, this kind of antenna is omni-directional antenna with low gain, which could be arranged as an array to improve the gain, however, the feed network of the array is too difficult to solve; b) wide slot antennas [6,7], including all kinds of wide-slot coupled feed antennas whose gains are low; c) antennas with resistance gradual changing structure, including some ultra-wideband directional antennas, such as Vivaldi antenna [8], TEM horn antenna [9], ridged horn antenna [10], etc. However, most of these kinds of antennas are limited by their large volume for certain applications; d) frequency independent antennas, including equiangular and Archimedean spirals, log-periodic dipole antennas, and so on.…”