Beam Steering Range Enhancement of Bifocal Reflectarray Using Irregular Distribution of Meta-atoms

This article reports the feasibility of significantly improving the maximum beam steering range of conventional bifocal reflectarrays (BiRAs) from ±30° (as reported in the literature) to ±70°. Unlike the periodic BiRAs in the literature, the beam steering range improvement in this work is realized via breaking the symmetry (periodicity) along x- and y-axes and using an irregular (aperiodic) distribution of meta-atoms on the BiRA aperture. This is accomplished without the need to optimize the reflection phase using complicated and time-consuming algorithms. The geometric phased meta-atoms of the proposed irregular BiRA are distributed without any transitional periodicity in the xy-plane in a way similar to the distribution of seeds of a sunflower. Bifocal parabolic phase distribution is imposed on all the aperiodic geometric phased meta-atoms across the irregular BiRA aperture. It is shown that the proposed BiRA with irregular distribution of geometric phased meta-atoms can realize 140°(±70°) beam steering range (with less than 3 dB gain loss) from 14 GHz to 24 GHz. The maximum measured gain is 26.8 dBi at 19 GHz, and a maximum aperture efficiency of 50.9%.