Wideband diffuse scattering and RCS reduction of microstrip antenna array based on coding metasurface

In this communication, wide-angle monostatic radar cross section (RCS) reduction of a metal plate is reported. The whole angular range (0°–90°) is divided into three parts according to the different dominant scattering mechanisms. Each dominant scattering mechanism is accurately identified and suppressed effectively. Frequency selective surface (FSS) absorber is employed to reduce the specular echo intensity within the first angular part. The tapered resistive sheets (TRSs) are loading as an edge termination to the metal layer and FSS layer, respectively, providing a slowly varying surface current to taper the transition between the free space and the targets. Significant RCS reduction in the rest two angular parts is achieved. Simulation results clearly show that more than 10 dB monostatic RCS reduction is realized within a wide angular range (0°–10° and 30°–85°) for the frequency band ranging from 1.3 to 2 GHz. Samples have been fabricated and measured in the anechoic chamber, and a remarkable agreement between the simulation and measurement is obtained. The effectiveness of the design is fully verified.

In this paper, a switchable radar cross section (RCS) reduction between the two broadbands' (1-7 GHz and 4-10 GHz) has been achieved by just considering the integration of hybrid frequency selective surface (FSS) based phase cancelation structure (PCS) with a modified ground square patch antenna operating at 2.4 GHz. The full metallic ground plane of the conventional microstrip antenna (MSA) is replaced by a 2 × 2 array of band-stop FSS having the same frequency as that of the MSA. This ground plane modification helps to increase the maximum out-of-band RCS reduction from 16.4 dB to 20 dB. The ground modified MSA without any PCS exhibits both in-band and out-of-band maximum RCS reduction of 20 dB over a wideband (1-7 GHz). A new approach is adopted to form the PCS. It is formed by placing two non-overlapping hybrid FSSs at different heights above the MSA. The MSA with FSS based ground plane along with the hybrid FSS based PCS exhibits good monostatic and bistatic RCS reduction across 4 to 10 GHz without affecting the radiation characteristics of the conventional MSA. The measured results show a close resemblance to the simulated ones.

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.

This letter proposes a dielectric dartboard metasurface, which achieves broadband monostatic radar cross section (RCS) reduction and evenly bistatic scattering. Two types of dielectric elements with different permittivity are alternately arranged on a metallic plate as a dartboard structure. By choosing the thickness of the dielectric, the phase difference of 180° ± 37° between elements is obtained to meet the condition of phase cancellation for RCS reduction. Simulation results show that the design achieves 84% (4.5–11 GHz) fractional bandwidth of 10 dB monostatic RCS reduction and evenly distributed bistatic RCS pattern. We fabricated a prototype to verify this design, the measurement and simulation results are in good agreement.

This paper presents a radar cross-section (RCS) reduction technique by using the coding diffusion metasurface, which is optimised through a random optimization algorithm. The design consists of two unit cells, which are elements ‘1’ and ‘0’. The reflection phase between the two-unit cells has a 180° ± 37° phase difference. It has a working frequency band from 8.6 GHz to 22.5 GHz, with more than 9 dB RCS reduction. The monostatic RCS reduction has a wider bandwidth of coding diffusion metasurface as compared to the traditional chessboard metasurface. In addition, the bistatic performance of the designed metasurfaces is observed at 15.4 GHz, which shows obvious RCS reduction when compared to a metallic plate of the same size. The simulated and measured result shows the proficiency of the designed metasurface.

Metasurface provides an efficient method to regulate wave propagation in multiphysics fields ranging from light waves, electromagnetic (EM) waves, and acoustic waves. Considering the versatile demands in practical scenarios, the essential challenge is to design the metasurface with spectral compatibility to satisfy the various applications. Here, we proposed an optically transparent hybrid mechanism metasurface (HMM) incorporating absorption, polarization conversion, and phase cancellation mechanisms for wideband, wide-angle, and omnidirectional scattering suppression performance. The unit cell integrates absorption and polarization conversion capabilities by etching the indium tin oxide (ITO) film into the specific structure, exhibiting wideband ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.44-31.31$ </tex-math></inline-formula> GHz), wide-angle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!&lt; 45^{\circ }$ </tex-math></inline-formula> ), high-efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!\ge 90$ </tex-math></inline-formula> %), and omnidirectional co-polarized scattering suppression performance. Moreover, the phase cancellation mechanism is implemented by distributing the unit cell and its mirror structure in the chessboard configuration, which provides cross-polarized reflection reduction capability for the HMM. Therefore, the HMM achieves a significant total radar cross section (RCS) reduction by integrating multiple scattering suppression mechanisms. Eventually, the simulated and measured results indicate that the proposed HMM can realize more than 10 dB total monostatic and bistatic RCS reduction within 7.49-32.23 and 7.46-30.55 GHz, respectively. In addition, good specular and omnidirectional RCS reduction capabilities are also obtained. Furthermore, the HMM also presents good optical transparency, which is attributed to the high transmittance of the polyethylene terephthalate (PET) substrates and the ITO films. The proposed strategy has potential application in the multifunctional stealth design of stealth platforms.

The reflection variation property of Electromagnetic Band-Gap (EBG) structures can be utilized to reduce the Radar Cross Section (RCS) of ground planes. Combining PEC and EBG structures on the same ground plane forms checkerboard surfaces which can achieve a RCS reduction in a narrow frequency band. However, a wider band RCS reduction can be realized by combining two different EBG structures. It can realize 60% frequency bandwidth for the 10-dB RCS reduction. The scattered fields for square checkerboard surfaces are re-directed toward four quadrants, while the scattering for hexagonal checkerboard surfaces are toward six directions. The maxima of the RCS for checkerboard surfaces in the four quadrants are 10 dB less than those of the PEC ground plane, and more than 19 dB RCS reduction is obtained along the principal planes. Both bistatic and monostatic RCS are compared with those of the equal-sized PEC ground planes.

A phase gradient metasurface (PGM) with Jerusalem crosses is presented for radar cross section (RCS) reduction of curved surfaces. The PGM consists of supercells of which 8 different Jerusalem crosses are printed on a grounded F4B substrate. Using gradient reflection phases, the PGM can redirect the specular reflection into a predetermined direction and realize monostatic RCS reduction. Simulated results show that the PGM on the curved surface achieves an average RCS reduction of 6.7 dB. The presented PGM can be a potential solution of missile stealth.

This paper explores the mechanism of radar cross section (RCS) reduction under plasma. The Runge–Kutta exponential time differencing–finite difference time domain method is used to compute the radar cross section of a target covered by plasma. Then, a method for analyzing the electromagnetic coupling effect between electromagnetic waves and plasma-covering targets based on field intensity visualization images and a probe is proposed. This method can elucidate the interaction process between electromagnetic waves and plasma-covering targets, ultimately revealing the key finding that the complex multiple reflections between the air–plasma interface and the plasma–metal interface are the fundamental mechanism of radar cross section reduction. Furthermore, the influence of the electron density, collision frequency, plasma thickness, electromagnetic wave frequency, and non-uniform distribution characteristics on the radar cross section reduction is discussed. A radar cross section reduction ridge is discovered in a two-dimensional diagram of radar cross section variation with electron density and electromagnetic wave frequency. It can be observed that the places where radar cross section reduction is more significant all satisfy the condition that the frequency of the electromagnetic wave is slightly higher than the cutoff frequency of the plasma, which provides guidance for the design of plasma stealth parameters.

In this paper, we introduce an effective technique for designing diffusion electromagnetic (EM) surfaces with polarization and angle-insensitive characteristics over multiple wide bands. The proposed EM surface consists of a random pixelated metal structure in the middle of double substrate layers and a metallic ground at the bottom. Phase cancellation for radar cross section (RCS) reduction is achieved by different propagation paths generated by the pixelated metallic layer. The theoretical prediction of the reduction frequency band and reduction value is derived by transmission line theory, which serves as guidance to design the EM surface for the required operating band. Using this technique, an EM surface is designed for 10 dB RCS reduction over multiple frequency bands, and the first two reduction bands are 5.98–16.23 GHz and 26.69–37.1 GHz with fractional bandwidths of 92.3% and 32.6%, respectively. The non-reduction frequency band between the first two reduction bands is almost at the K-band (18–27 GHz), which is unusable for long-range transmission because of its high atmospheric loss. Moreover, the bandwidth of RCS reduction bands is stable for oblique incident angles up to 40° for both TE and TM polarizations. Based on theoretical study and simulation results, a prototype of this EM surface is fabricated and experimentally characterized. The theoretical analysis, simulation and experiment results are in good agreement. The proposed method comprehensively solves the problems of narrow bandwidth, time-consuming optimization of the unit cell, high bistatic RCS value, and sensitivity to polarization and incident angles found in recent RCS reduction research.

In this paper, we employed an efficient polarization conversion metasurface (PCM) to achieve broadband radar cross section (RCS) reduction for plane targets. Simulation results illustrate that the proposed “whale-shaped” unit achieves more than 90% polarization conversion ratio (PCR) in an ultra-broadband from 8.37 to 22.67 GHz. We combine the PCM unit into a 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3 scale lattice to form periodic structure. Subsequently, we employ the PCM lattice and its mirror lattice as “Lattice 0” and “Lattice 1” of digital coding. In order to achieve the best RCS reduction performance, we obtain the optimized combinational layout by utilizing information entropy theory and genetic algorithm. Different from the traditional checkerboard distribution, the optimized coding PCM realizes scattering beam diffusion in space. The fitting of measurements and simulations demonstrate that the proposed PCM realizes monostatic RCS reduction of −10dB in the ultra-broadband from 9.37 to 22.79 GHz. Simultaneously, the proposed optimized coding PCM operates over a wide-angle oblique incidence range from 0° to 45°. The proposed “whale-shaped” optimized coding PCM features both ultra-broadband operating bandwidth and high angular stability, which is informative for the practical application for PCMs.

This article presents an efficient and effective design approach of the phase distribution calculation across metasurface for significant radar cross section (RCS) reduction of a circular polarization (CP) and liner polarization (LP) radar waves. The RCS reduction using the proposed design approach is achieved by imposing a novel cusp phase mask (which is usually used to generate 3D self-accelerating and self-healing cusp beams) at each geometric phased anisotropic unit cell composing the proposed cusp phased metasurface. By solving the cusp phase formula using MATLAB, it is found that the cusp phase mask required to achieve more than 10 dB of RCS reduction over a wide frequency band can be calculated without the need of significant lengthy optimizations or huge computer resources. The ability of such cusp phase mask metasurfaces to achieve significant backward scattering and RCS reduction has been rigorously investigated by means of simulations and measurements. When illuminated by a far-field radar CP or LP plane wave, the proposed cusp phased metasurface realizes more than 10 dB of RCS reduction from 10.9 to 26 GHz, corresponding to a fractional bandwidth of FBW = 81.8%. The 10 dB RCS reduction bandwidth of the cusp metasurface is maintained under both normal and wide angular incidence up to 75∘. The proposed cusp metasurfaces have potential applications to make objects stealthy where the incidence radar signal has an unknown frequency, polarization, or angle of incidence.

In this paper, we present a metasurface composed of complementary units that can realize orthogonal linear and linear-to-circular polarization conversion in multi-band. Linear polarization conversion has seven high-conversion frequency bands: 9.1–9.7 GHz, 15.6–17.6 GHz, 19.4–19.7 GHz, 21.2–23.1 GHz, 23.5–23.8 GHz, 26.2 GHz, and 27.9 GHz. Linear-to-circular polarization conversion also has seven frequency bands with axial ratios (ARs) less than 3 dB: 8.9–9.0 GHz, 9.9–14.7 GHz, 19.1–19.3 GHz, 23.2–23.35 GHz, 23.4 GHz, 24.1–25.4 GHz, and 27.2–27.8 GHz, with the generation of multiple bands extended by the combination of complementary units. Then, we utilize the combined polarization conversion unit’s mirror placement to form a 4 × 4 array to realize the phase difference cancellation of the reflective field, giving the metasurface the radar cross section (RCS) reduction function and the dual-band 10-dB monostatic RCS reduction bandwidth: 8.9–9.7 GHz and 15.5–26.1 GHz. The measured and simulated results were essentially identical. Because the design uses the complementary units to form an array to expand the polarization conversion frequency bands, it provides a novel idea for future designs and can be applied to multiple microwave frequency bands.

In this paper, an all-metal magneto-electric dipole (ME-dipole) antenna array working in the S-band is proposed, featuring radar cross section (RCS) reduction in the X-band achieved through phase cancellation. To realize stealth performance in the X-band, a kind of RCS reduction units with a chessboard configuration is designed. For verification, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2 \times 2$</tex> antenna array operating in the S-band (2.36–2.92 GHz) with RCS reduction capability in the X-band (8.0-12.0 GHz) is constructed. Simulation results demonstrate that the monostatic RCS of the proposed antenna array is reduced by more than 10 dB across the entire X-band under normal plane wave incidence. Furthermore, the integration of the X-band RCS reduction units preserves the original array footprint without any dimensional expansion.

A single-layer polarization converting metasurface (PCMS) with wideband is presented for polarization conversion and radar cross-section (RCS) reduction. The proposed PCMS is composed of metallic biconic shape resonator imprinted on a metal-backed F4BM dielectric substrate of relative permittivity 2.2 and loss tangent 0.001. The unit cell has a compact size of 0.16 $\lambda_\mathrm{o} \times 0.16\lambda_\mathrm{o}$ . A comprehensive parametric analysis, angular sensitivity study, bistatic and monostatic RCS analysis are conducted by illuminating the proposed PCMS using linearly polarized (LP) plane waves. The PCMS converts LP electromagnetic waves to their orthogonal polarization state in the frequency band of 8.7–24.8 GHz resulting in polarization conversion ratio over 90% with a fractional bandwidth of 96%. Additionally, the developed structure is applied in chessboard configuration, using phase cancellation techniques for RCS reduction, that achieve 10 dB RCS reduction across a wideband of 7.9–23.4 GHz. The unit cell and its rotated version has a cross-polarization reflection phase difference of ( ${180}\pm {37}{^\circ}$ ) in the operating band, which fulfill the criteria for RCS reduction. The chessboard configuration exhibits a scattering pattern with four strong lobes that deviates from the normal incident path because of the phase cancellation in normal direction. The experimental results are in good agreement with the simulated result. Applications for the developed structure include antenna design (gain enhancement and beam steering), target hiding, imaging, and microwave communications.