Angle and Polarization Insensitive RCS Reduction Metasurface Based on Hybrid Mechanism of Polarization Conversion and Absorption

ABSTRACTThis paper presents a single‐layer multi‐bit coding polarization conversion metasurface (MCPCM) designed for the attainment of broadband and wide‐angle radar cross section (RCS) reduction. The metasurface unit possesses a symmetrical structure composed of a bidirectional arrow and a defective rectangular ring, making it polarization‐insensitive to electromagnetic (EM) waves. The designed metasurface unit exhibits broadband polarization conversion efficiency across the frequency spectrum of 11.2–25.6 GHz, achieving a polarization conversion rate (PCR) beyond 90% and displaying four resonance points. We obtained multi‐bit phase responses with phase differences of 180°, 90°, and 45° through the optimized design of the unit's structure. A discrete artificial bee colony (DABC) algorithm optimizes the coding sequence, enhancing RCS reduction performance. Compared with an equivalently sized perfect electric conductor (PEC), the optimized MCPCM achieves over 10 dB RCS reduction within the 11–25 GHz frequency range. Additionally, the optimized MCPCM achieves a broader RCS reduction bandwidth compared to traditional chessboard‐patterned metasurfaces. Furthermore, we investigated the proposed MCPCM's bistatic RCS performance, achieving substantial RCS reduction over a broad spectrum of incident angles. Simulation and measurement results validate the proposed metasurface capability for effective EM wave manipulation, demonstrating its potential for broadband and wide‐angle RCS reduction.

An ultra wideband (UWB) radar cross-section (RCS) reduction metasurface has received attention in recent years. However, the majority of the research has concentrated on the physics and design of planar surfaces, which do not meet the standards of modern aerodynamics and aesthetics. In this paper, we offer a sophisticated strategy for designing a metasurface that can conform to the shape of any object, even those of moderate curvature, and can also achieve UWB RCS reduction by combining absorption, polarization conversion, and diffusion mechanisms. Firstly, an absorbing-polarization converter is designed, composed of a square patch with a truncated diagonal strip and ring. A thin Rogers RT/Duroid 5880 dielectric substrate layer is used in the structure, which is also appropriate for conformal conditions. The substrate layer and the ground plane are separated by an air gap to enhance the polarization conversion bandwidth (PCBW). For normal incident electromagnetic (EM) waves, the PCBW ranges from 10.8 to 31.3 GHz with polarization conversion ratio (PCR) values greater than 0.9 dB. Up to a 45∘ oblique incidence angle over the aforementioned band, the PCR efficiency is well maintained. Then, the optimized coding metasurface is formed by the Pancharatnam–Berry (PB) phase, consisting of meta-atoms “0” and “1” of the same size but different orientations, to realize the concept of cross-polarization diffusion. A theoretical investigation has been performed to analyze the RCS reduction performance of planar as well as conformal cylindrical surfaces. The results show that more than 10 dB of RCS reduction is experienced over UWB (10.8–31.3 GHz) for planar metasurfaces under linearly and circularly polarized incidence waves. Furthermore, the RCS reduction for cylindrical surfaces can be achieved in a similar frequency band above 10 dB up to an angle of 90∘. It can be deduced that our proposed flexible metasurface can be used as an absorber or a polarization converter and provide broadband RCS reduction, which is essential for multi-function and conformal stealth applications.

Phase modulation of metasurfaces for polarization conversion and RCS reduction

A new design method for ultrabroadband radar cross section (RCS) reduction by exploiting characteristic complementary polarization conversion metasurfaces (PCMs) is proposed and validated. The proposed method lifts the conventional bandwidth limitation enforced by the performance of a single PCM and expands the RCS reduction bandwidth. A systematic strategy for ultrabroadband RCS reduction design is developed and an effective reflection coefficient amplitude of the composite surface ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Gamma _{ {eff}}$ </tex-math></inline-formula> ) is derived as a new RCS reduction indicator. Based on this indicator, complete polarization conversion (CPC) frequency points of PCM are identified as important characteristics, and PCM pairs with interleaved CPC points, termed as initial PCM (I-PCM) and complementary PCM (C-PCM), are designed to compensate each other for ultrabroadband RCS reduction. A scaling-and-tuning two-step method for designing the C-PCM of a specific I-PCM is developed and validated. To further improve RCS reduction performance, taking the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Gamma _{ {eff}}}$ </tex-math></inline-formula> as an indicator, the particle swarm optimization (PSO) algorithm is used to select the optimal I-PCMs, C-PCMs, and their area ratios. Finally, an ultrabroadband RCS reduction surface is designed, fabricated, measured, and validated. It realizes 10-dB monostatic RCS reduction ranging from 7.6 to 26.2 GHz (110.7% relative bandwidth) which exceeds the polarization conversion bandwidth of each individual PCM. Besides, good polarization insensitivity and bistatic RCS reduction performance are also obtained. The proposed method provides a new route for designing broadband RCS reduction surface based on PCMs with unsatisfactory characteristics and greatly alleviates the performance requirement for PCMs.

Based on polarization conversion and destructive interference, a novel monolayered metasurface is proposed for ultrawideband monostatic and bistatic radar cross section (RCS) reductions for both copolarization and cross polarization. Unit cells share a simple asymmetric double arrow shape, but with variable geometry parameters, correspondingly with different polarization conversion capabilities and different reflection coefficients. The particle swarm optimization (PSO) algorithm and array theory are combined to optimize and select appropriate parameters for unit cells. The optimized unit cells (O-cells) simultaneously realize the polarization conversion and destructive interference to reduce copolarized RCS. In addition, mirrors of these O-cells (M-cells) are adopted to achieve the complete destructive interference to reduce cross-polarized RCS. Therefore, the total monostatic RCS can be greatly reduced. To improve the bistatic RCS reduction, random distribution of unit cells is carefully designed to realize diffusion patterns. In both the simulation and measurement results, a 10 dB monostatic RCS reduction at the normal incidence is achieved from 7.5 to 22.5 GHz (100% bandwidth). Furthermore, good specular and bistatic RCS reduction performances under oblique incident waves are also obtained. The proposed methodology opens up a new route for ultrawideband RCS reduction.

In this paper, we present a design of the linear polarization conversion metasurface (MS) for the broadband radar cross section (RCS) reduction based on split-ring resonator (SRR) structure in microwave region. The corresponding phase gradient can be obtained through the stable phase difference of basic units of polarization conversion MS. The designed polarization conversion MS is applied in coded electromagnetic (EM) matrix by defining two basic units “0” and “1”, respectively. Based on the principle of planar array theory, a new random coding method named by matrix-type coding is proposed. Correlative RCS reduction mechanism is discussed and verified, which can be used to explore the RCS reduction characteristic. The simulated linear polarization conversion rate of the designed structure is up to 90% in the frequency range of 6–15 GHz, and the RCS reduction results verify the theoretical assumptions. Two kinds of matrix-type coding MS samples are prepared and measured. The experimental results indicate that the reflectance of MS is less than –10 dB on average under normal incidence in frequency range of 5.8–15.5 GHz. The average RCS reduction is essentially more than 10 dB in frequency range of 5.5–15 GHz and the corresponding relative bandwidth is 92.7%, which reasonably agrees with simulation. In addition, excellent RCS reduction characteristic of the designed MS can also be achieved over a wide incident angle.

In this letter, a zigzag shaped polarisation conversion metasurface (PCM) operating in terahertz (THz) band is presented for polarisation conversion and wideband radar cross section (RCS) reduction. The proposed PCM unit cell array and its mirror unit cell array are organised in chessboard type configuration to exploit the reflection phase cancellation property for wide band RCS reduction. Upon simulation, the proposed PCM achieves polarisation conversion ratio (PCR) of more than 90% within the frequency region of 1.42 THz to 3.56 THz. Above 10 dB, monostatic RCS reduction is obtained in the frequency region of 1 THz to 4 THz, with a peak RCS reduction of 23 dB at 2.89 THz.

This paper proposes a dielectric-enhanced high-density stacking resistive frequency selective surface (RFSS) absorber with a dual-section step-impedance design for wide-band and wideangle radar cross section (RCS) reduction. A fundamental relationship between the input impedance and permittivity of the non-resonant absorber at high frequencies was formulated, facilitating an inverse design of the dielectric-enhanced high-density stacking RFSS structure with customized dispersion properties. An equivalent circuit model was developed for the dual-section step-impedance configuration. The configuration was optimally designed through dispersion engineering to achieve broadband absorption performance. Simulated and measured results demonstrate that the proposed absorber achieves an RCS reduction better than 10 dB from 2.1 to 18 GHz under normal incidence. Under oblique TE-polarized incidence, it provides approximately 10 dB of RCS reduction over 0-70° at 2, 6, and 10 GHz. Meanwhile, under TM-polarized oblique incidence, it maintains over 10 dB RCS reduction within 0-75° at the same frequencies. These results validate the effectiveness of the proposed analytical methodology and design strategy.

A novel metasurface design is presented integrating polarization conversion, diffusion, and phase cancellation mechanisms for broadband radar cross-section (RCS) reduction. The metasurface employs a rotationally symmetric configuration, enabling efficient dispersion of electromagnetic waves in x and y polarizations. By changing the unit cell size, polarization conversion optimization is accomplished. This results in a 180phantom{0}^{circ } phase difference for the 1-bit design and 22.5phantom{0}^{circ } for the 2-bit design, with reflection magnitudes surpassing 0.9 in the 11.2-20.2 GHz and 12.3-19.5 GHz frequency ranges, respectively. The genetic algorithm (GA) was employed to optimize the arrangement of unit cells, identifying the most effective configuration for scattering and RCS suppression. Simulation results under LP normal incidence demonstrate significant RCS reduction capabilities. The 1-bit metasurface achieves approximately 10 dB RCS reduction across 12.3-19.2 GHz, corresponding to a relative bandwidth of 43.81%. In contrast, the 2-bit metasurface achieves a 20 dB decrease inside 12-19.3 GHz (relative bandwidth 46.65%) and a wider 10 dB reduction over 11.1-20.3 GHz (relative bandwidth 58.60%), with a peak reduction of roughly 15 dB in the 13.5-15.4 GHz range. Additionally, co-polarized reflections produced by the Pancharatnam-Berry (PB) phase or unit cell rotation introduce continuous phase discrepancies, which aid in efficient wave manipulation. Under LP oblique incidence, the metasurface demonstrates robust performance. Over 12.3-18.9 GHz, the 1-bit design retains RCS reduction of 10 dB up to a 15phantom{0}^{circ } incidence angle (relative bandwidth 42.3%), while the 2-bit design extends this capability up to a 30phantom{0}^{circ } incidence angle across 12-19.3 GHz (relative bandwidth 46.65%). Both simulated and experimental results validate the metasurface’s ability to manipulate electromagnetic waves and achieve effective RCS reduction, highlighting its potential for advanced stealth and electromagnetic wave control applications.

With the continuous development of detection technology, single detection technologies such as radar and infrared (IR) can no longer meet the current detection needs. The design of metamaterials is gradually moving towards multispectral compatible design. In this work, a polarization converter with low IR emissivity and a checkerboard metasurface with radar-IR bi-stealth were proposed. The filling rate of indium-tin-oxide(ITO) is increased to reduce the IR emissivity without affecting the polarization conversion efficiency. In addition, based on the radar cross section (RCS) reduction theory of the checkerboard composed of polarization conversion units, a broadband RCS reduction radar-IR bi-stealth structure is designed and analyzed. A sample was fabricated and the IR and microwave characteristics of the metasurface were measured. The numerical simulation results are in good agreement with the measurement results. The results show that the polarization conversion rate (PCR) is higher than 90% in the frequency range of 7.98-12.02 GHz, and the axial ratio (AR) is between 0.5 and 2 in the frequency range of 6.92-7.56 GHz and 12.48-15.78 GHz for the proposed polarization converter. The RCS reduction of the checkerboard metasurface exceeded 10 dB in the frequency range of 7.7-11.8 GHz. Meanwhile, the IR emissivity is less than 0.3 in 8-14 µm and the structure exhibits good optical transparency. This indicates the potential application of the proposed structure in multifunctional and multispectral compatible materials.

In this paper, a novel method of realizing the ultra-wideband (UWB) radar cross section (RCS) reduction is proposed. We combine the chessboard structure of multi-elements which are all polarization conversion metasurface (PCM) units with random coding. Four different kinds of PCM units all with UWB and much high polarization conversion rate (PCR) are selected. Morever, their polarization conversion frequency bands are optimized not only in the high frequency segment but also in the low frequency segment. The final designed structure can achieve 10 dB RCS reduction within 6.9 GHz–20.1 GHz in the high frequency segment and 15.5 GHz–51.2 GHz in the low frequency segment, respectively. In addition, the effects of RCS reduction by the square chessboard structure composed of different numbers of these PCM units are compared. The proposed metasurface structure provides an efficient scheme to reduce the scattering of the electromagnetic waves.

This paper presents a wideband Fabry-Perot (FP) antenna with gain enhancement and Radar Cross Section (RCS) reduction using symmetrical polarization conversion metasurface. Two kinds of symmetrical polarization conversion units are etched on both sides of the dielectric substrate with chessboard arranged to form the Polarization Conversion Metasurface (PCM). The simulation results show that the FP antenna has the 10-dB impedance matching band of 8.65-12.05 GHz (32.9%), the maximum gain of 17.09 dBi, the 3-dB gain bandwidth of 8.68-11.48 GHz (27.8%), and the RCS reduction band is 8-26 GHz with peak RCS reduction of 18.06 dB at 11.5 GHz.

In this work, an ultra-wideband reflective polarization conversion metasurface (PCM) is proposed at first. Because the PCM is an anisotropic structure that is symmetric with respect to both x- and y-axes, and the reflection phase difference under x- and y-polarized incidences is close to 180° in an ultra-wide frequency range, the PCM can achieve both linear polarization conversion and circular-polarization (CP) maintaining reflection in the ultra-wide frequency band from 8.3 to 41.3 GHz except for near the frequency point of 38.8 GHz. Moreover, when its unit cell structure is rotated by 90°, its cross-polarized reflection coefficient under LP incidence, together with the co-polarized reflection coefficient under CP incidence, will be changed by almost 180° in phase. Thus, based on the PCM, an ultra-wideband coding diffusion metasurface (CDM) is further proposed for radar cross section (RCS) reduction. The simulation and experiment results indicate that the CDM can achieve effective RCS reduction in the ultra-wide frequency band of 8.2–41.7 GHz under normal incidence with arbitrary polarization; in addition, an ultra-wideband RCS reduction can still be realized under oblique incidence with an incident angle less than 45°, which shows that the CDM is of good application value in radar stealth technology.

RCS reduction effect based on transparent and flexible polarization conversion metasurface arrays

In this paper, an absorptive coding metasurface (ACM) is proposed for ultra-wideband radar cross section (RCS) reduction, the design process is presented in detail, in which a lossy polarization conversion metasurface (PCM) is proposed at first. The lossy PCM is an anisotropic resistive structure with both polarization conversion and absorption performances, so that its co-polarization reflection coefficients under u- and v-polarized incidences can be kept at less than − 10 dB in magnitude in the frequency range from 7.5 to 45.2 GHz. Though the magnitude of the cross-polarization reflection coefficient cannot be very small only due to the absorption, its phase will be changed by nearly 180° when the unit-cell structure of the lossy PCM is rotated by 90°. Thus, the lossy PCM can be used as one of the two types of lossy coding elements for an ACM when its unit-cell structure is rotated by 90° or not. Based on the lossy PCM, an ACM is proposed. The simulation and experimental results show that the ACM has an excellent RCS reduction performance under arbitrary polarized incidence, it can achieve effective RCS reduction under normal incidence in the ultra-wide frequency band from 7.4 to 45.5 GHz with a ratio bandwidth (fH/fL) of 6.15:1; moreover, an ultra-wideband RCS reduction can still be achieved when the incident angle is increased to 45°, which indicates that the ACM has good stealth performance under the detection of various radars working in X, Ku, K and Ka bands, it is very practical.