Multi-band Reflective Metasurface for Efficient Linear and Circular Polarization Conversion

2025-02-14 Fri
Metasurface Multi-band Linear-Linear Polarization Linear-Circular Polarization Polarization Conversion
Multi-band Reflective Metasurface for Efficient Linear and Circular Polarization ConversionResearch Background and Problem StatementIn modern communication, radar systems, and remote sensing technologies, the control of electromagnetic wave polarization is a key technology. By manipulating the polarization state of electromagnetic waves, signal transmission quality can be optimized, interference reduced, and overall system performance enhanced. Traditional polarization conversion devices are often bulky and have limited efficiency, while metasurface technology, which has emerged in recent years, offers new possibilities to address these issues. A metasurface is a two-dimensional metamaterial composed of an array of sub-wavelength “meta-atoms” that can control the properties of light or electromagnetic waves with nanoscale precision.
However, although many studies have explored the polarization conversion capabilities of metasurfaces within single or dual frequency bands, designing a reflective metasurface that can simultaneously achieve efficient linear-to-linear (LLP) and linear-to-circular (LCP) polarization conversion across multiple frequency bands remains a challenge. Additionally, in practical applications such as satellite communications and radar systems, devices need to maintain stable performance over a wide range of incident angles. Therefore, developing a reflective metasurface with multi-band operational capability, high polarization conversion efficiency, and good angular stability holds significant importance.
Source of the PaperThis paper, titled “Multi-band Reflective Metasurface for Efficient Linear and Circular Polarization Conversion,” was authored by Jamal Zafar, Humayun Zubair Khan, and others. The first author and corresponding authors are affiliated with the School of Engineering at the University of Glasgow (UK) and the Department of Electrical Engineering at the National University of Sciences & Technology (Pakistan). The paper was published in the 2025 issue of Optical and Quantum Electronics and is assigned the DOI: 10.1007/s11082-025-08037-y.
Research Methods and Experimental Proceduresa) Research Workflow and Experimental DesignThe study is divided into several key steps:
1. Unit Cell Design and Theoretical AnalysisThe researchers initially designed a three-layer unit cell-based metasurface, including a top metallic textured layer, an intermediate dielectric substrate (Rogers RO3003, relative permittivity $\epsilon_r = 3.00 \pm 0.04$), and a bottom metallic ground plane. By adjusting the unit dimensions and geometry, they achieved coverage across the X-band (8–12 GHz), Ku-band (12–18 GHz), and K-band (18–27 GHz).
To validate its functionality, the research team conducted simulations using CST Microwave StudioⓇ software in the frequency-domain Floquet mode. These simulations not only considered the reflection coefficients under normal incidence but also tested performance up to a 45° tilt angle. Notably, the researchers employed U-V decomposition to analyze the cross-polarization conversion mechanism by decomposing the incident wave along the U and V axes and calculating the reflection coefficients and phase differences in each direction.
2. Sample Fabrication and Experimental MeasurementsAfter completing the simulations, the researchers fabricated a prototype metasurface consisting of a 40×28 array of unit cells. The sample was patterned with high precision using laser-assisted etching on copper layers to ensure accurate realization of the complex unit design. Subsequently, they built a free-space real-time experimental platform using a broadband horn antenna (frequency range 2–18 GHz) as both transmitter and receiver, combined with an Agilent PNA network analyzer (model N5224A) to measure the reflection coefficients. During the experiment, the researchers recorded co-polarization (Co-polarization) and cross-polarization (Cross-polarization) reflection coefficients and compared the simulation results with experimental data.
3. Data Analysis AlgorithmsThe researchers used the following formula to evaluate the Polarization Conversion Ratio (PCR):
$$
\text{PCR} = \frac{r{yx}^2}{r{yx}^2 + r{xx}^2} = \frac{r{xy}^2}{r{xy}^2 + r{yy}^2}
$$
Here, $r{yx}$ and $r{xy}$ represent the cross-reflection coefficients, while $r{xx}$ and $r{yy}$ represent the co-reflection coefficients. Additionally, they used Axial Ratio (AR) and Ellipticity values to quantify circular polarization performance.
b) Key Research Findings1. Efficient Linear-to-Linear Polarization ConversionSimulation results showed that the PCR of this metasurface exceeded 90% in three sub-bands: 9.12–9.57 GHz, 13.08–14.07 GHz, and 18.84–19.23 GHz, even maintaining this level at a 45° tilt angle. This indicates excellent performance in linear-to-linear polarization conversion.
2. Circular Polarization Conversion CapabilityFor Left-Hand Circular Polarization (LHCP) and Right-Hand Circular Polarization (RHCP), the study found that the metasurface achieved effective conversion in the ranges of 8.37–8.97 GHz and 14.50–18.66 GHz (LHCP), as well as 9.78–12.71 GHz and 19.35–19.67 GHz (RHCP). Specifically, the Axial Ratio (AR) remained below 3 dB, and the Ellipticity values were close to ±1, demonstrating its stability across a wide frequency band.
3. Experimental Validation and Error AnalysisExperimental results were highly consistent with simulation data, with only minor deviations likely due to fabrication defects or noise in the measurement environment. For example, some central frequencies exhibited shifts of approximately 2 dB, but the overall trend remained consistent. This consistency further confirms the reliability of the design.
c) Research Conclusions and SignificanceThis study successfully developed a multi-band reflective metasurface capable of efficient linear-to-linear and linear-to-circular polarization conversion across the X, Ku, and K bands. Compared to existing designs, this metasurface has the following advantages:
1. High-Frequency Operation: Supports multi-band operation covering the X, Ku, and K bands.
2. High Conversion Efficiency: Achieves a PCR exceeding 90% across all target frequency bands.
3. Good Angular Stability: Maintains excellent performance even at a 45° tilt angle.
4. Compact Design: Uses commercially available materials (e.g., Rogers RO3003), making it suitable for mass production.
From a scientific perspective, this research advances the technical progress of metasurfaces in the field of polarization conversion; from an application standpoint, it provides new solutions for wireless communications, radar systems, and remote sensing technologies.
d) Research HighlightsInnovative Design: By introducing dual-slotted ring and stripe structures, it achieves synergistic effects of low-frequency and high-frequency resonances.
Versatility: Simultaneously supports linear-to-linear and linear-to-circular polarization conversions, applicable to various scenarios.
Angular Stability: Maintains high performance across a wide range of incident angles, addressing common angular dependency issues in traditional designs.
Summary and Future OutlookThe proposed multi-band reflective metasurface in this paper represents significant progress in the field of polarization conversion. Its efficiency, stability, and versatility make it a strong candidate for future communication and sensing technologies. Future research could further explore its potential applications in Reconfigurable Intelligent Surfaces (RIS) and how it can be integrated into more complex systems.