Broadband Reflectarray Antennas Using Double-Layer Subwavelength Patch Elements

This letter investigates a novel bandwidth improvement method, which combines the multilayer approach with the subwavelength element technique. A new definition of phase error has been introduced to quantitatively analyze the performance of the reflectarray elements. It is shown that double-layer subwavelength elements exhibit a superior phase performance across the band, namely an increased phase range and a reduced phase error over frequency. Numerical analysis is then performed to calculate the bandwidth of reflectarray antennas using these elements, where the practical fabrication tolerances at high frequencies are considered. Finally, a 1-dB gain bandwidth of 19.1% has been demonstrated for a double-layer -band reflectarray using elements with a periodicity of λ/4.