In this paper, a design procedure for a linearly polarized ultra-wide band (UWB) single layer reflectarray antenna (RA) is presented. The RA is comprised of novel unit cells of annular ring patches; each ring is connected to two phase delay lines to achieve a linear and smooth phase response over a wide frequency range. In the proposed RA, the designed true phase delay provides more than three cycles of 360°. By adjusting the length of these phase delay lines, a wide range of 1300° linear phase variation has been obtained over a wide frequency band. A wide bandwidth and low cross-polarization (XP) levels were predicted using the utilized novel unit cell element and the elegant mirrored arrangement. To validate the simulated results, a prototype of circular aperture with 22.86 cm diameter was fabricated and its radiation patterns were measured. The measured 3-dB gain bandwidth of the RA is 40%, and its maximum gain, aperture efficiency and XP levels are 19.3 dB, 69% and − 35 dB, respectively, which are in good agreement with simulation.