Multiband linear and circular polarization rotating metasurface based on multiple plasmonic resonances for C, X and K band applications

Khan M.I., Hu B., Chen Y., Ullah N., Khan M.J., Khalid A.R.

In this letter, multiband efficient asymmetric transmission is realized both numerically and experimentally in the microwave frequency regime, using a three-layered chiral metasurface (CMS). The proposed structure achieves propagation direction dependent polarization transformation where the plane of polarization is rotated by 90° for x/y polarization in the backward/forward direction. The asymmetric polarization transformation functionality for linearly polarized impinging waves is accomplished in three frequency bands: 10.9–11.2 GHz, 14.4–14.8 GHz, and 18.4–18.5 GHz. Moreover, the structure has a robust response to the variation of incidence angle (up to 40°). The measurement results of the fabricated structure are found to be in good agreement with the numerical results.

Fahad A.K., Ruan C., Ali S.A., Nazir R., Haq T.U., Ullah S., He W.

Polarization converters play an important role in modern communication systems, but their wide and multiple band operation to facilitate volume and size reduction is quite challenging. In this paper, a triple-band Linear Polarization to Circular Polarization (LP-to-CP) converter is presented using a novel design procedure based on geometric parameters optimization of a metasheet. The proposed converter is ultrathin, wideband, stable over a wide range of incident angles, and polarization diverse. The conductor layer of metasheet is patterned with a square ring and five square-patches diagonally intersecting each other. To validate the proposed method, an LP-to-CP convertor in X-band (7.3~9.6 GHz) and dual Ka-bands (25.4~31.4 GHz, 35.4~42.2 GHz) is presented. The performance is quite stable in wide range of frequencies and against the variation of incident angles from −25° to 25°. After performing model-based theoretical paradigm analysis, and full-wave simulation and optimization, the converter is fabricated and the measurements are performed inside the anechoic chamber. The measured results, close to simulation results, depict the validity and reliability of the proposed design.

Khan M.I., Hu B., Amanat A., Ullah N., Khan M.J., Khalid A.R.

Yu Y., Xiao F., He C., Jin R., Zhu W.

We present experimentally a double-arrow metasurface for high-efficiently manipulating the polarization states of electromagnetic waves in the dual-band. The metasurface is capable of converting a linearly polarized (LP) incident wave into a circularly polarized (CP) wave or its cross-polarized LP wave at different frequencies. It is numerically shown that in the two bands from 14.08 to 15.71 GHz and from 17.63 to 19.55 GHz the metasurface can convert the LP wave into CP wave, of which the axis ratio is lower than 3 dB. Meanwhile, the proposed metasurface also can convert the LP wave into its cross-polarized LP wave at 13.39 GHz and 20.29 GHz. To validate the theoretical analysis and simulated results, a prototype is fabricated and measured. The experimental results are reasonably consistent with the theoretical and simulated results, which demonstrates that such a metasurface can successfully achieve dual-band and dual-mode polarization conversion.

Khan M.I., Khalid Z., Tanoli S.A., Tahir F.A., Hu B.

In this paper, metasurface based multi-band polarization converter is designed and demonstrated. The designed metasurface does not only convert horizontal polarization into vertical and vice versa, but also exhibits linear-to-circular and circular-to-linear polarization conversion. The proposed design efficiently converts linearly polarized incident wave into cross-polarized wave within three frequency bands: 6.3-6.6 GHz, 9-10.8 GHz and 15.2-18.2 GHz. Similarly, linear-to-circular and circular-to-linear polarization conversion is achieved in six frequency bands: 6-6.1 GHz, 6.9-7 GHz, 7.1-7.2 GHz, 8-8.7 GHz, 11.3-13.4 GHz and 13.5-14.5 GHz. Moreover, both linear-cross and linear-to-circular polarization conversion maintain their conversion efficiencies against variations in the incidence angle. The physical mechanism is explained using surface current distribution. The proposed metasurface is validated by full wave simulation and experimental verification.

Zhang X., Li S.

Multiband linear-to-circular (LTC) metamaterial converters have promising applications in modern optical system. However, it is challenging to design a converter with conversion bands of more than four and the axial ratio of less than 3 dB due to the coupling interaction of different resonant structures in a unit cell. In this article, we demonstrate a broad class of self-complementary THz infinite thin metasurfaces composed of supercells of fractal metal rectangular patches and holes dimers of spanning 1 THz octave in bandwidth, while still being highly efficient. The advantages of this converter are as follows. The device is theoretically nonthickness; the LTC polarization conversion can be achieved in both the reflected and transmitted fields; the phase difference between two orthogonal linear polarization components is theoretically 90° in any frequency. Therefore, an eight-band LTC converter is achieved in reflection and transmission modes. This new nonthickness multiband device will demonstrate a major advance toward an LTC synthetic metasurface in the THz band.

Li S.J., Cui T.J., Li Y.B., Zhang C., Li R.Q., Cao X.Y., Guo Z.X.

Liu W., Yu T., Sun Y., Lai Z., Liao Q., Wang T., Yu L., Chen H.

Wave plates are important optical components for controlling the polarization state of light, in scientific research as well as commercial applications. Traditional wave plates are not achromatic, and more elaborate designs typically rely on stacking of different wave plates and system optimization to extend the operating bandwidth. Here the authors demonstrate that broadband wave plates can be obtained by engineering the mode dispersion in a single layer of subwavelength gratings featuring high refractive-index contrast. This achievement will contribute to the design of compact, fully integrated polarization converters for practical applications.

Zheng Q., Guo C., Ding J.

A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y/x-polarized incident EM wave can be converted to the x/y-polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y/x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.

Xu J., Li R., Qin J., Wang S., Han T.

We report the design, fabrication, and measurement of an ultra-broadband wide-angle reflective cross-polarization convertor using the compact H-shaped metasurface. The significant bandwidth expansion is attributed to the four electromagnetic resonances generated in an H-shaped unit. The simulation results show that the polarization conversion ratio (PCR) of the proposed metasurface is above 90% in the frequency range from 7 to 19.5 GHz and the relative bandwidth reaches 94%. The proposed metasurface is valid for a wide range of incident angles, and the mean polarization conversion ratio remains 80% even though the incident angle reaches 41.5°. The experimental results are in good agreement with the simulation results. Compared with the previous designs, the proposed linear polarization converter has a simple geometry but an excellent performance and hence has potential applications in microwave communications, remote sensors, and imaging systems.

Loncar J., Grbic A., Hrabar S.

A polarization converting metasurface that operates in the X-band is designed and fabricated. The metasurface converts a linearly polarized incident electromagnetic wave to an orthogonal polarization upon reflection. The design has a subwavelength thickness of 1.27 mm (0.04 λ), a half-power bandwidth of 22%, and a polarization conversion ratio of 99.4%. The metasurface was fabricated with a low-cost printed circuit board process. It is realized by cascading three patterned metallic sheets in order to achieve the desired polarization conversion and high reflection. The polarization conversion is accomplished by guiding and coupling electromagnetic energy between pairs of orthogonal slots in a ground plane, placed at the edges of each unit cell. The performance of an experimental prototype showed close agreement with simulation.

Kwon D., Ptitcyn G., Díaz-Rubio A., Tretyakov S.A.

For transmissive applications of electromagnetic metasurfaces, an array of subwavelength Huygens' metaatoms are typically used to eliminate reflection and achieve a high transmission power efficiency together with a wide transmission phase coverage. We show that the underlying principle of low reflection and full control over transmission is asymmetric scattering into the specular reflection and transmission directions that results from a superposition of symmetric and anti-symmetric scattering components, with Huygens' meta-atoms being one example configuration. Available for oblique illumination in TM polarization, a meta-atom configuration comprising normal and tangential electric polarizations is presented, which is capable of reflectionless, fullpower transmission and a $2\pi$ transmission phase coverage as well as full absorption. For lossy metasurfaces, we show that a complete phase coverage is still available for reflectionless designs for any value of absorptance. Numerical examples in the microwave and optical regimes are provided.

Lin B., Guo J., Chu P., Huo W., Xing Z., Huang B., Wu L.

Metasurfaces offer a convenient means to control the polarization state of light. Converting linear polarization (LP) and maintaining circular polarization (CP) in reflection mode have been widely realized, but these two types of polarization control have not been achieved using a single metasurface. This article reports an anisotropic metasurface that allows both multiband LP conversion and CP-maintaining reflection, due to the anisotropy of the metamaterial's unit cell. This system facilitates ultrawide-band polarization converters for $e.g.$ antennas, wireless communication, and radar technology.

Khan M.I., Tahir F.A.

Khan M.I., Tahir F.A.

A highly flexible single-layer metasurface manifesting quarter-wave plate as well as half-mirror (1:1 beam-splitter) operation in the microwave frequency regime is being presented in this research. The designed metasurface reflects half power of the impinging linearly polarized electromagnetic wave as circularly polarized wave while the remaining half power is transmitted as circularly polarized wave at resonance frequency. Similarly, a circularly polarized incident wave is reflected and transmitted as linearly polarized wave with equal half powers. Moreover, the response of the metasurface is quite stable against the variations in the incidence angle up to 45°. The measurements performed on the fabricated prototype exhibit a good agreement with the simulation results. The compact size, flexible structure, angular stability and two in one operation (operating as a quarter-wave plate and beam-splitter at the same time) are the main characteristics of the subject metasurface that makes it a potential candidate for numerous applications in communication and miniaturized and conformal polarization control devices.

Zafar J., Khan H.Z., Jabbar A., Kazim J.U., Rehman M.U., Siddiqui A.M., Abbasi Q.H., Imran M.A.

Abstract This work proposes a novel multi-band reflective metasurface, that is capable of linear polarization (LP), and circular polarization (CP) conversion in Ku, K, Ka, and U Bands. The metasurface design involves a combination of ring and square elements strategically arranged, and printed on a 0.76 mm thin-grounded Rogers RO3003 substrate. The metasurface achieves LP for y-polarized incident electromagnetic (EM) wave in 16.2–17.2 GHz, 23.0–25.4 GHz, 40.3–54.35 GHz frequency bands. The polarization conversion ratio (PCR) for LP frequency ranges is minimum 90% with an fractional bandwidth (FB) of 2.94%, 9.91%, and 26.9%, respectively. Moreover, metasurface achieves CP for y-polarized incident EM wave in 16.1–16.55 GHz, 17.5–22.15 GHz, 26.65–37.75 GHz, and 55.6–59.8 GHz frequency bands. In addition, the axial ratio (AR) for CP frequency ranges is less than 3 dB with a FB of 2.75%, 23.45%, 34.47%, and 7.27%. The device performance is considerably stable under oblique incidences up to 45 degrees. The metasurface unitcell is compact with a structural size of $$\text {length}=0.23\lambda _\circ$$ , $$\text {width}=0.23\lambda _\circ$$ and $$\text {thickness}=0.08\lambda _\circ$$ . The proposed prototype is fabricated, and the measured results are in good agreement with the simulated one. Overall, the proposed metasurface exhibits promising performance characteristics and holds potential for multiple applications in satellite based networks.

Tian H., Li J., Wu Y., Wang X.

Hafeez S., Yu J., Umrani F.A., Yun W., Ishfaq M.

Multifunctional integrated meta-devices are the demand of modern communication systems and are given a lot of attention nowadays. Most of the research has focused on either cross-polarization conversion (CPC) or linear-to-circular (LP–CP) conversion. However, simultaneously realizing multiple bands with good conversion efficiency remains crucial. This paper proposes a multiband and multifunctional dual reflective polarization converter surface capable of converting a linearly polarized (LP) wave into a circularly polarized (CP) wave, in frequency bands of 12.29–12.63 GHz, 16.08–24.16 GHz, 27.82–32.21 GHz, 33.75–38.74 GHz, and 39.70–39.79 GHz, with 3 dB axial ratio bandwidths of 2.7%, 40.15%, 14.6%, 13.76%, and 0.2%, respectively. Moreover, the converter is capable of achieving CPC with a polarization conversion ratio (PCR) that exceeds 95%, within the frequency ranges of 13.10–14.72 GHz, 25.43–26.00, 32.46–32.56 GHz, and 39.14–39.59 GHz. In addition, to identify the fundamental cause of the CPC and LP–CP conversion, a comprehensive theoretical investigation is provided. Furthermore, the surface current distribution patterns at different frequencies are investigated to analyze the conversion phenomena. A sample prototype consisting of 20 × 20 unit cells was fabricated and measured, verifying our design and the simulated results. The proposed structure has potential applications in satellite communications, radar, stealth technologies, and reflector antennas.

Maurya V., Singhal S.

Yazdani-Shavakand M., Ahmadi-Shokouh J., Dashti H.

This paper proposes a new framework based on the characteristic modes analysis (CMA) to design polarization conversion metasurfaces (PCMs). This approach relies on the information inferred from the characteristic currents of the dominant modes (DMs). To demonstrate the advantages of this strategy, a multi-functional PCM is designed for the X-band frequencies. Besides, this paper expands and develops the characteristic mode rotation (CMR) method to investigate the intrinsic behavior of PCMs. Based on the extended CMR method, the physical concepts behind polarization conversion purity and angular stability at the resonance frequencies are revealed in a new manner. Finally, a prototype of the designed polarizer is fabricated and its reflection coefficients are measured. A great agreement between simulation and measurement results is obtained.

Ahmed A., Cao Q., Khan M.I., Shah G., Ahmed F., Khan M.I., Ul Abidin Z.

Abstract In this paper, a chiral metasurface is presented to effectively attain an ultra-broadband operation of asymmetric transmission with highly efficient cross-polarization conversion. The efficiency of the asymmetric transmission operation in the frequency band ranging from 6.5 to 13 GHz is above 70%. Additionally, in the frequency range from 3.7 to 14 GHz, the cross-polarization conversion realizes greater than 90% polarization conversion ratio. Asymmetric transmission as well as cross-polarization conversion show angular stability against the incident angle of electromagnetic waves up to 45°. To validate the simulation results, the fabricated chiral metasurface is tested and compared with simulation results. The concepts of asymmetric transmission and linear-polarization conversion are demonstrated and physically explained through the distributions of surface currents over metallic layers. This anticipated work has significant applications in telecommunications and radar, as well as potential use in equipment designed for the manipulation of electromagnetic waves.

Danaeifar M.

The bound state in the continuum (BIC) is exploited to metasurfaces for the purpose of arising strong confinement of light and high quality (Q) factor resonances. In this paper, a BIC symmetry-protected metasurface consisting of rectangular graphene patches is synthesized and realistically modeled with intrinsic losses in a far-infrared regime. The quasi-BIC with three asymmetry approaches is applied to attain strong tailored confinement of the incident light, and the resulting resonances with tailored line widths and selective confinement of light are exhibited. Asymmetry parameters of length, rotation, and material feature of chemical potential regulate dual specifications of resonance linewidth and intensity. Efficiency analysis of the results illustrates that rotation asymmetry is the foremost among the three suggested methods, and it establishes the highest Q-factor of 945 with an achievable asymmetry parameter of 5.5%. The high Q and tunable resonances realized in the graphene quasi-BIC metasurfaces promise various practical applications in the infrared spectra, such as narrow band filters, sensors, optical switches, and light-matter interaction platforms.

Ahmed A., Cao Q., Khan M.I., Sajjad M., Ahmed F.

Abstract In this paper, a bi-layered ultra-thin multifunctional chiral metasurface is proposed to obtain asymmetric transmission (AT), cross-polarization conversion (CPC), and circular dichroism (CD). The multifunctional chiral metasurface realizes AT with more than 70% efficiency over a frequency range of Ku-band from 14.3 to 15.8 GHz, while in the operating frequency band from 13.5 to 16.2 GHz, the CPC ratio is above 90%. In addition, the metasurface exhibits CD in the K-band with a CD parameter of 0.6 at 24 GHz. Furthermore, the functionalities of AT and CPC are stable for changes in incident angle up to 60° for both transverse-electric (TE) and transverse-magnetic (TM) electromagnetic (EM) waves. For verification of the anticipated concept, the proposed chiral metasurface is fabricated and measured. The proposed design can be used for potential applications in the Ku- and K-bands for satellite communication and radar.

Jalal A., Qasim M., Qureshi U.U., Hu B.

Abstract This paper investigates a single-layered active anisotropic meta-surface design capable of achieving high polarization conversion efficiency over a 6G communication band gap. Additionally, the designed structure can convert the linear polarization of the incoming wave fronts to its cross-polarization and linear polarization to circular polarization in the reflection mode. The polarization conversion characteristic is achieved due to the strong anisotropic behavior of the meta-surface. Such a simple design can achieve a 90% to 100% cross-polarization conversion efficiency over a frequency region of [0.28-0.36] THz. The linear to circular polarization conversion is performed near 0.26 THz and 0.40 THz. Between these two frequencies, band linear to cross-polarization conversion is more prominent. The proposed design can be tuned from a half-wave plate (HWP) or linear polarization converter to a quarter-wave plate (QWP) or circular polarization converter using the chemical potential of graphene. The optical response of the meta-surface behaves differently from different incident angles. The proposed polarization converter can contribute to the development of active polarization device.

Shankar S., Upadhyay D.K.

Jalal A., Bin H., Qureshi U.U., Qasim M., Khan A.

Wu J., Wang X., Xiao H., Wang Y., Fan Z., Zhang H.

Abstract In this paper, we propose a wide-incidence-angle insensitive reflective metasurface multi-polarization converter, using split-ring-resonators and cross oscillators structure. The simulated results indicate that the polarization conversion ratio for linear to linear (LTL) polarization conversion is greater than 90% in three frequency bands of 5.03–5.19 GHz (3.13%), 6.38–6.82 GHz (6.67%) and 7.38–7.44 GHz (0.81%). Meanwhile, the axial ratio for linear to circular (LTC) polarization conversion is less than 3 dB in four frequency bands of 4.79–5 GHz (4.29%), 5.24–6.27 GHz (17.90%), 6.94–7.35 GHz (5.74%) and 7.45–7.48 GHz (0.40%). LTL or LTC polarization conversion will not be affected when the incidence angle is tilted by 45° under both transverse electric and transverse magnetic modes. To verify the polarization conversion performance, a sample consisting of 18 × 18 unit cells is fabricated and measured. The measured results are found to be in reasonable agreement with the simulated results, demonstrating the potential application of this design for future microwave polarization state manipulation.

Li Z., Wu B., Yang M., Sheng X.

Li E., Li X.J., Seet B., Ghaffar A., Aneja A.

This paper presents a metasurface-based linear-to-circular polarization converter with a flexible structure for conformal and wearable applications. The converter consists of nested S- and C-shaped split ring resonators in the unit cell and can convert linearly polarized incident waves into left-handed circularly polarized ones at 12.4 GHz. Simulation results show that the proposed design has a high polarization conversion rate and efficiency at the operating frequency. Conformal tests are also conducted to evaluate the performance under curvature circumstances. A minor shift in the operating frequency is observed when the converter is applied on a sinusoidal wavy surface.

Turkmen-Kucuksari O.

In this study, a reflective multi-functional metamaterial polarization converter printing two connected metal rings and two unconnected metal square patches on a metal backed FR4 substrate is designed in S/C/X Bands. The lowest operating frequency of the proposed polarizer is starting from 2.41 GHz. Linear to linear (LTL) polarization conversion at three bands: 2.41–2.52 GHz, 3.77–4.16 GHz, and 7.02–7.37 GHz as well as linear to circular (LTC) polarization conversion at 7 bands: 2.35–2.38 GHz, 2.58–2.65 GHz, 3.49–3.63 GHz, 4.32–4.36 GHz, 6.73–6.86 GHz, 7.5–7.62 GHz, 9.77–9.87 GHz are achieved in this design. Both numerical simulations and experimental validation are provided for this polarization converter. Performance of the proposed and some referenced polarization converters are also compared to represent the advantages of the proposed design.