In this article, a novel and high-efficiency dual-wideband linear-to-circular polarization conversion based on a rectangular-slot reflective metasurface is anticipated, one that can convert linearly polarized (LP) electromagnetic waves into right- and left-hand circularly polarized waves in two non-adjacent frequency bands. The converter is an orthotropic design, with a pair of mutually orthogonal symmetric axes (u and v) along orientations tilted at 45° to the y-axis. The simulated results

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... cate that the dual-wideband circularly polarized wave is achieved under a y-polarized an electromagnetic (EM) incidence wave over the bands of 16.49–23.54 GHz and 26.44–34.56 GHz with 3 dB axial ratio relative bandwidths of 35.23% and 26.62%, respectively, and a polarization conversion ratio (PCR) in excess of 99%. A detailed mathematical investigation is proposed to determine the fundamental factor causing the dual-wideband linear-to-circular polarization conversion. The phase difference (∆φuv) between ruu and rvv under u- and v- polarized incident waves is ±90°, and it entirely determines the 3 dB reflected wave axial ratio. Any reflective converter can work efficiently as a linear-to-circular polarization conversion if the phase difference (∆φuv) is close to ±90°.