It is decomposed into a vertical component E ⊥ → and a horizontal component E ∥ →. The incident plane wave E i n → is tilted 45° with respect to the principal axis of the modulator. It consists of one (or more) sheet(s) of meander-C-shaped conductors. The general principle for the metasurface modulator is shown in Fig. 1(a).
Section snippets The Smith chart representation of the metasurface modulator All the results are verified by the full-wave simulation method. This clear physical image display can give designers correct direction and achieve rapid design. The impedance of the metasurface pattern can be exhibited in the Smith chart so that the designers obtain the impedance information and reflection/ transmission coefficient information, and the relationship between them. In this paper, the Smith chart method is proposed to design polarization modulator that transforms a linear polarized wave into a circularly polarized wave. However, the design methodology of polarization modulator based on metasurfaces have rarely been reported. Owing to their unique features, metasurfaces have been applied to modulate the polarization of EM waves, and various polarization modulators have been proposed from microwaves to terahertz frequencies ,, ,. Metasurfaces, as the two-dimensional (2D) equivalence of metamaterials, are attracting a steadily growing interest from researchers in both science and engineering communities owing to their unparalleled EM properties and compact size, enabling the control of the material constitutive parameters in terms of values, distributions, anisotropy, and chirality with artificial structures ,, ,,. Hence, it is urgent to develop new materials. However, with the higher demand for practical application, the defects of traditional methods are becoming more apparent, such as narrow wavelength range and bulky design. The previous methods to modulate the polarization employ the birefringence in crystals and the variation of the spatial profile of the refractive index . Because the polarization of EM waves is invariant and independent of the time and frequency domains, PoM is compatible with other modulation techniques and has been adopted in conventional wireless communication systems to achieve a higher data rate, larger capacity, and higher frequency utilization efficiency to suppress interference from the environment ,, ,,. It provides an additional degree of freedom for the carrier waves . Polarization modulation (PoM), which exploits the state of polarization of EM waves as the information-bearing parameter, has been proposed as an alternative to standard modulation techniques, such as amplitude shift keying, frequency-shift keying, phase-shift keying, and differential phase-shifting keying. Polarization, amplitude, and phase are the three basic characteristics of electromagnetic (EM) waves and the modulations of polarization, amplitude, and phase spatial dispersions are the core of modern photonic and microwave devices. The Smith chart method will also be helpful in the design of other metasurface-based devices, such as metasurface absorbers. According to the Smith chart analysis, we obtained a single-layer modulator with 50% efficiency and a three-layer modulator with 100% efficiency, all of which are verified using the full-wave simulation method. We show that the parameter changes in the pattern can be directly displayed in the Smith chart, which provides clear physical image guidance to designers. The proposed method bridges the metasurface pattern and its equivalent circuit impedance. In this study, we introduce the Smith chart method to guide the design of metasurface-based modulator that transforms a linearly polarized wave into a circularly polarized wave. Metasurfaces have provided unprecedented freedom for modulating the polarization state of electromagnetic waves. Polarization modulation (PoM) provides an additional degree of freedom for the modulation of carrier waves and may be an alternative to conventional wireless communication techniques that use amplitude, frequency, and phase modulations.
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