In order to realize the ultra-wideband radar with phased array function, the balanced Vivaldiantenna is selected as the array unit, and the Vivaldi antenna array is simulated under the cyclic boundary conditions, which can realize the scanning angle of E-plane and H-plane in the frequency band of 4~12 GHz to reach ±60°, and the active standing wave ratio is less than 3. However, the balanced Vivaldi antenna array based on dielectric substrate is not easy to be installed in space-limited locations because of its high profile. So a pure metal stepped slot-line antenna with lower profile is designed. The third order pure metal stepped slot-line antenna is simulated under the periodic boundary conditions, and the same radiation performance as the balanced Vivaldi antenna can be realized. The scattering performance of the two antennas is compared with a 6×6 rectangular grid array as an example, and the overall scattering value of the pure metal stepped slot-line antenna is lower, which has a significant advantage in horizontal polarization. In the triple frequency bandwidth, the pure metal stepped slot-line antenna array has the same radiation performance as the Vivaldi antenna array, but the former antenna has a lower profile, higher structural strength, and better performance in low scattering performance.