An ultra wide band antenna having a 270° coverage and a system thereof. The ultra wide band antenna includes a dielectric substrate, two Vivaldi horn radiators attached to the dielectric substrate and including central axes orthogonal to each other, and a single radiator coupled to the two Vivaldi horn radiators. The ultra wide band antenna system includes: a first ultra wide band antenna including a dielectric substrate, two Vivaldi horn radiators attached to the dielectric substrate and including central axes orthogonal to each other, and a single radiator coupled to the two Vivaldi horn radiators; and a second ultra wide band antenna including a dielectric substrate, two Vivaldi horn radiators attached to the dielectric substrate and including central axes orthogonal to each other, and a single radiator coupled to the two Vivaldi horn radiators, positioned on an identical plane to the first ultra wide band antenna, and forming a line symmetric structure together with the first ultra wide band antenna.