Ultra-wideband (UWB) patch antenna for Ku/K band applications is presented. In this paper, a microstrip line feed has been modified to an elliptical gradient structure, and the conventional radiator patch has been developed through the use of the symmetrically circular slots. These modifications have been used to improve the performance of the antenna significantly. Upper and lower frequency ranges achieve UWB antenna performances start from 11.57 GHz to 21.45 GHz. Proposed antenna exhibits good impedance matching, which makes it convenient to work in various applications. Besides that, the reflection coefficient is reduced attained to -31.81 dB over the operating band. The antenna is developed and analyzed using the commercially available software FEKO simulator based on the method of moments (MoM). Other parameters results such as sidelobe level (SLL) and beamwidth (half power - 3 dB) are added and discussed significantly. The proposed design is fabricated and tested experimentally, and the results show that a satisfying agreement with the simulation results.