Investigations on bandwidth improvement of reflectarrays using single-layered sub-wavelength double circular ring elements

In an effort to improve the bandwidth of the single layer reflectarray, this paper investigates the use of double concentric circular ring elements arranged in a range of sub-wavelength grids on a single layer of substrate. The double concentric circular ring elements used here allow an additional degree-of-freedom to improve the bandwidth. Based on the concentric ring element, four offset-fed 0.43m×0.43m (14.3λ×14.3λ) reflectarrays centered at 10 GHz with various element periodicities, namely λ/2, λ/3, λ/4 and λ/5 grids, are designed and developed. The measured results show that among the four reflectarrays, the one with λ/4 grid spacing achieves the broadest 2-dB gain bandwidth of 33% with an aperture efficiency of 36.2%.