In this study, we design an implementable high-performance wideband flat reflector based on conformal transformation optics. By eliminating sharp edges in the virtual space, the refractive index in the vicinity of the edges increases, which eventually reduces the device dispersion. The optical path rescaling method is employed to overcome the sub-unity refractive index issue, resulting in an all-dielectric isotropic graded-index medium that is physically implementable. The refractive index profile is split into eleven layers, each having a specific refractive index value. The proposed antenna requires only isotropic dielectric layers with permittivity of 1.1–3.8, making it realizable. Simulation results of three-dimensional structure show that the proposed flat reflector can operate in a wide frequency bandwidth. The simulated antenna gain is about 25.27–29.55 dBi in the 13–30 GHz frequency range with a side-lobe level below − 15 dB. The proposed antenna was designed and simulated using COMSOL Multiphysics, and simulation results are validated using the CST Studio Suite.