Bandwidth improvement of reflectarrays using single‐layered double concentric circular ring elements on a subwavelength grid

This article proposes the use of double concentric circular ring elements arranged in a subwavelength grid on a single layer of substrate, in an effort to increase the bandwidth of reflectarrays. Compared to the traditional λ/2 grid arrangements, radiating elements arranged in subwavelength grids achieves a more similar behavior over wider frequency bands when radiating elements' parameters are varied; albeit with a smaller reflected phase range. Furthermore, in contrast to conventional subwavelength single‐patch designs that have only one variable parameter of the phasing element, the double concentric circular ring elements also allow additional degrees‐of‐freedom to improve the bandwidth. Based on the concentric ring element, two offset‐fed 0.43 × 0.43 m 2 reflectarrays, one with λ/2 grid and another with λ/3 grid, centered at 10 GHz are designed and developed. The measured results show that the 2‐dB gain bandwidth of the one with λ/2 grid spacing is 13.6%, whereas the one with λ/3 grid spacing is 24.4%.