This paper presents a compact microstrip-fed ultra-wideband (UWB) antenna and its four-element array design for target detection applications. A prototype was fabricated and then measured based on optimal parameters. There is good consistency between the simulated S11 and the measured one. In addition, a 1 × 4 linear array design with the size of 100 mm × 34 mm has been proposed to achieve a higher gain. Simulation shows that the array gain is increased about 6 dBi in comparison to the single element through the whole UWB frequency range of 3.1 GHz to 10.6 GHz. The proposed array has an average of −15 dB side lobe level (SLL) in the mentioned range. And also, a −23 dB SLL has been achieved by applying Dolph-Chebyshev amplitude distribution at 6 GHz. Simulation results confirm that the antenna exhibits a constant bidirectional radiation pattern with a high and flat gain in case of the array design.