An enhanced reflectarray (RA) antenna built of elements with reduced reflection phase sensitivity is presented. The proposed unit element is composed of a concentric, multiresonance circular-ring structure with variable sizes. By changing the outer and inner radius of the interior ring in the opposite directions, a reduction in the phase sensitivity to manufacturing inaccuracy is achieved without extra contribution to the 360° phase range and aggravating the losses in the unit element is achieved. In addition, the margin between normal and oblique incidence of a phase response for angles up to 40° is smaller than 10°, which results in a high-efficiency, wideband performance. Measurement results show the maximum gain of 26.4 dBi at 10 GHz, aperture efficiency of 44.27%, and 16.3% 1 dB gain bandwidth. In order to improve the bandwidth of antenna, the phase constant (ψ0) value at the RA aperture is gradually tuned and optimized. The designed antenna with ψ0= 1250 has a peak gain 26.6 dBi at 10.2 GHz and aperture efficiency of 44.56%, and the 1 dB gain bandwidth is about 23.3% (9.67-12 GHz). In comparison with the conventional antenna (ψ0= 0°), the 1 dB bandwidth shows a 43% improvement.
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Mohammadi et al. (2018) studied this question.