A single‐layer high‐efficiency ultra‐wideband reflectarray by using quasi‐spiral dipole

In this communication, a single‐layer ultra‐wideband element composed of quasi‐spiral dipole is proposed. For the symmetry of the element structure, the element has the same phase response for horizontal, vertical, and circular polarization so that the reflectarray can achieve corresponding polarization if a feed with linear or circular polarization illuminates the reflectarray. For the structure of the quasi‐spiral dipole element, 360° linear phase shift in a wide band (9‐19GHz) is achieved in a small space and it can expand the bandwidth through the sub‐wavelength structure. Compared to the traditional two‐degree‐of‐freedom element, the element can achieve a 360° phase shift in a wide bandwidth and the phase curve is nearly parallel to each other. A 270 mm × 270 mm (27 × 27 elements) reflectarray is designed and fabricated based on the proposed elements. The simulation results almost agree with the measure results. The measured 1‐dB gain bandwidth about 44% (11.5‐18GHz) is achieved and 68% of aperture efficiency at 12GHz, which demonstrates wideband operation for the proposed reflectarray.