Wideband Radar Cross Section Reduction Research Articles

A Wideband Polarization-Insensitive Bistatic Radar Cross-Section Reduction Design Based on Hybrid Spherical Phase-Chessboard Metasurfaces

A wideband polarization-insensitive bistatic radar cross-section (RCS) reduction design under linear and circular polarization incidence is proposed based on spherical-chessboard metasurfaces. A new metasurface element with wideband characteristics was designed, including a double split-ring structure, single-layer media, and metal board. In the proposed RCS-reduction design, the Pancharatnam–Berry (P-B) phase theory is applied with the designed metasurface element to realize phase distribution mimicking the low-scattering sphere, and thus realizing RCS reduction. In addition, the chessboard configuration is combined with spherical phase distribution to further improve the performance of monostatic and bistatic RCS reduction. Finally, the proposed RCS reduction design can not only realize wideband RCS reduction but also exhibit polarization-insensitive characteristics. It realized 10 dB monostatic and bistatic RCS reduction in a frequency band ranging from 8.5 to 21 GHz (84.8% relative bandwidth) under linear polarization (LP) and circular polarization (CP) incidence. The straightforward and efficient design method of the hybrid spherical chessboard can effectively avoid the complex and time-consuming optimization process in RCS-reduction design.

Wideband radar cross-section reduction by a double-layer-plasma-based metasurface

Reduction of the radar cross-section (RCS) is the key to stealth technology. To improve the RCS reduction effect of the designed checkerboard metasurface and overcome the limitation of thin-layer plasma in RCS reduction technology, a double-layer-plasma-based metasurface—composed of a checkerboard metasurface, a double-layer plasma and an air gap between them—was investigated. Based on the principle of backscattering cancellation, we designed a checkerboard metasurface composed of different artificial magnetic conductor units; the checkerboard metasurface can reflect vertically incident electromagnetic (EM) waves in four different inclined directions to reduce the RCS. Full-wave simulations confirm that the double-layer-plasma-based metasurface can improve the RCS reduction effect of the metasurface and the plasma. This is because in a band lower than the working band of the metasurface, the RCS reduction effect is mainly improved by the plasma layer. In the working band of the metasurface, impedance mismatching between the air gap and first plasma layer and between first and second plasma layers cause the scattered waves to become more dispersed, so the propagation path of the EM waves in the plasma becomes longer, increasing the absorption of the EM waves by the plasma. Thus, the RCS reduction effect is enhanced. The double-layer-plasma-based metasurface can be insensitive to the polarization of the incoming EM waves, and can also maintain a satisfactory RCS reduction band when the incident waves are oblique.

Wideband Radar Cross Section Reduction of a Coding Metasurface Combined With an Inhomogeneous Plasma

Wideband Radar Cross Section Reduction of a Coding Metasurface Combined With an Inhomogeneous Plasma

Wideband high-efficiency scattering reduction in a graphene based optically transparent and flexible metasurface

Metasurfaces with scattering field suppression properties play a crucial role in electromagnetic protection and stealth strategies, benefiting both civilian and military sectors. Despite significant efforts dedicated to exploring methods for radar cross-section (RCS) reduction, the design of wideband devices with high-efficiency scattering reduction remains a substantial challenge. As a unique two-dimensional material, graphene, characterized by its ultra-thin profile, exceptional mechanical strength, and high carrier mobility, presents a new perspective for stealth technology. In this paper, we propose a novel graphene-based optically transparent and flexible metasurface, achieving high-efficiency RCS reduction across a wide frequency band. Employing multilayer stacking and doping of graphene, reverse-phase absorption cells with wideband characteristics have been successfully fabricated, enabling effective RCS reduction over a broadband through both phase cancellation and absorption mechanisms. The structure has undergone validation through both simulation and experimentation, exhibiting significant scattering suppression exceeding 20 dB in the frequency range of 10.3–19.2 GHz, and maintaining a reduction exceeding 10 dB from 6.3 to 21.4 GHz. Furthermore, simulation analysis indicates that the metasurface demonstrates remarkable polarization stability and robustness against large-angle incidences. In curved applications, the device attains a wideband RCS reduction of 15 dB at a bending angle of 15 degrees, and continues to surpass 10 dB even at an angle of 150 degrees. This graphene-based metasurface provides a pioneering approach for achieving near-perfect electromagnetic stealth.

Transparent and Ultra-Thin Flexible Checkerboard Metasurface for Radar-Infrared Bi-Stealth.

This paper proposed a single-layer checkerboard metasurface with simultaneous wideband radar cross-section (RCS) reduction characteristics and low infrared (IR) emissivity. The metasurface consists of an indium tin oxide (ITO)-patterned film, a polyethylene terephthalate (PET) substrate and an ITO backplane from the top downwards, with a total ultra-thin thickness of 1.6 mm. This design also allows the metasurface to have good optical transparency and flexibility. Based on phase cancellation and absorption, the metasurface can achieve a wideband RCS reduction of 10 dB from 10.6 to 19.4 GHz under normal incidence. When the metasurface is slightly cylindrically curved, an RCS reduction of approximately 10 dB can still be achieved from 11 to 19 GHz. The polarization and angular stability of the metasurface have also been verified. The filling rate of the top ITO-patterned film is 0.81, which makes the metasurface have a low theoretical IR emissivity of 0.24. Both simulation and experimental results have verified the excellent characteristics of the proposed checkerboard metasurface, demonstrating its great potential application in radar-IR bi-stealth.

Multilayer metasurface-based sandwich composites for wideband radar cross section reduction

Metasurface-based sandwich composites are designed here to achieve radar cross section (RCS) reduction within a wide frequency band. The RCS reduction is realized by spatially arranging the constitutive unit cells with different reflection phases. The proposed composites consist of a metasurface core sandwiched between the glass fiber and carbon fiber reinforced skins. Single-, two- and four-layer metasurfaces are designed respectively to reveal the influence of the layer number on the bandwidth of RCS reduction. It is indicated that the RCS reduction bandwidth can be substantially expanded by increasing the layer number of the metasurfaces. Finally, we fabricate a prototype consisting of four-layer metasurfaces and the RCS reduction property is measured in an anechoic chamber. The experimental results indicate that the fabricated metasurface-based composite can achieve −10 dB RCS reduction from 2.2 to 15.7 GHz, displaying a good agreement with the simulations. It is believed that our proposal may find potential applications in the radar stealth field.

Tapered Resistive Sheets and FSS Absorber Loading for the Wideband RCS Reduction of the Elliptic Surface at TM Polarization

A wide-band radar cross section (RCS) reduction of the elliptic surface at TM polarization is reported in this communication. The main scattering sources and the corresponding scattering mechanisms of the elliptic surface are accurately identified based on the ISAR imaging technique and the high-frequency approximation theory. The frequency selective surface (FSS) absorber is employed to suppress the specular reflection, and the tapered resistive sheets (TRSs) are used to handle the scattering from the trailing edges. Samples have been fabricated and measured in the anechoic room, both the simulation and measurement results illustrate that 10-dB RCS reduction is achieved within 1.35-4.9 GHz at TM polarization.

Wideband RCS reduction based on a simple chessboard metasurface

To avoid being detected by radar, it is necessary to reduce stealthy military platforms' radar cross section (RCS). The operation of overlaying the metasurface (MS) on the targets is a good solution. A simple chessboard MS structure that can achieve low RCS over a large bandwidth is proposed. Only one unit cell is used to construct the MS. First, the unit cell working in 0.5 and 1−λ modes is designed to achieve a stable phase difference of 180° for y- and x-polarized waves. Then, the unit cells and rotated ones are used to form a chessboard structure with different distributions. The compared results show that the chessboard MS with 2 × 2 quadrants can facilitate the widest 10 dB RCS reduction band of 111% and the largest RCS reduction. The proposed structure exhibits excellent RCS reduction even when irradiated by y- and x-polarized waves at an oblique incidence of 30°.

Realization of Single-Layer Fourier Phased Metasurfaces for Wideband RCS Reduction

An efficient and fast strategy to design and realize single layer Fourier phased metasurfaces for wideband radar cross section (RCS) reduction when illuminated by a circular polarization (CP) plane wave is proposed in this letter. The scattering phase (between 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> and 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> ) required at each unit cell of the proposed metasurfaces was computed using the Fourier phase formula in which the focal length ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> ) is inversely proportional to the phase distribution. Pancharatnam-Berry (PB) phase theory was applied with unit cells of subwavelength periodicity to further enhance the scattering and RCS reduction characteristics. The proposed wideband Fourier phased metasurface has a square shape and contains 30 × 30 PB unit cells with subwavelength periodicity of 5 mm ≈ 0.26λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16GHz</sub> . Both simulation and measured results show that the proposed Fourier phased metasurfaces can achieve more than 10 dB of RCS reduction under normal incidence of CP plane wave regardless of the value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> . Under oblique incidence, more than 10 dB of RCS reduction was maintained for incident angles up to 60°. In addition, the single-layer Fourier phased metasurface features wideband 10 dB RCS reduction bandwidth from 10 GHz to 24 GHz with a thickness of only 2 mm. This resulted in an 82.3% fractional bandwidth (FBW) of RCS reduction which is higher than other designs reported in the literature. The proposed design strategy provides a promising way to design and realize metasurfaces for wideband and stable RCS reduction performance without the need to use a computationally complex and/or time-consuming and slow running optimization algorithm.

Wideband RCS Reduction Based on Hybrid Checkerboard Metasurface.

Traditional stealth technologies all have their problems such as high cost and large thickness. To solve the problems, we used novelty checkerboard metasurface in stealth technology. Checkerboard metasurface does not have as high conversion efficiency as radiation converters, but it has many advantages such as small thickness and low cost. So it is expected to overcome the problems of traditional stealth technologies. Unlike other checkerboard metasurfaces, we improved it further by using two types of polarization converter units to be arranged in turn to form a hybrid checkerboard metasurface. Because the checkerboard metasurface composed of one type of polarization converter units can have a relatively wide radar cross-section (RCS) reduction in bandwidth when two types of polarization converter units are arranged in turn to form a hybrid checkerboard metasurface and mutual compensation of the two polarization converter units can broaden RCS reduction band further. Therefore, by designing the metasurface to be independent from the polarization, the effect of RCS reduction can be insensitive to the polarization of the incoming EM waves. The experiment and simulation results showed the value of this proposed hybrid checkerboard metasurface for RCS reduction. Mutual compensation of the units is a new attempt in the field of checkerboard metasurfaces for stealth technology and proved to be effective.

Reconfigurable chessboard coding plasma-based dielectric resonator structure for RCS reduction

In this paper, reconfigurable chessboard coding plasma-based dielectric resonator structure for radar cross section reduction is investigated. The radar cross section (RCS) reduction is essential in military applications. The metallic conductor surface is covered with plasma-based dielectric resonator (DRA) unit-cells arranged in chessboard configuration. The plasma DRA unit-cell consists of concentric cylindrical ring filled with ionized plasma placed over FR4 dielectric substrate. The plasma ionization voltage values are tuned to reflect the electromagnetic wave with phase shift of 180° and equal amplitudes. The phase 0° state represents the logic “0” while the phase 180° state represents the logic “1”. The chessboard arrangement consists of super-cells with 0/1 logic states. Different sizes of uniform super-cells 3 × 3, 4 × 4, 6 × 6, and 12 × 12 unit-cells are investigated for maximum RCS reduction. The scattered beams are directed to (± 30°, 180° ± 30°), (± 25°, 180° ± 25°), (± 20°, 180° ± 20°), (± 15°, 180° ± 15°) and (± 10°, 180° ± 10°) for 3 × 3, 4 × 4, 6 × 6, 8 × 8, and 12 × 12 uniform super-cells, respectively. The RCS is reduced over a wide angle range reduction with − 18 dBm2 at the broadside direction and below − 32 dBm2 over the angular range from − 90° to 90° according to the super-cell size. The non-uniform allocation of unit-cells in the super-cell chessboard arrangement is investigated. The RCS reduction bandwidth extended from 8.5 to 9.65 GHz. The scattered beam produces null in the broadside direction with wideband RCS reduction. The proposed structures are simulated using CST-MWS electromagnetic simulator.

Screen Printed Polarization Independent Microwave Absorber for Wideband RCS Reduction

Designing and deploying a broadband microwave absorber that provides wide bandwidth radar cross section (RCS) reduction for planar and curved surfaces is challenging. We present a resistive ink-based multilayered wideband absorber using a low-priced FR4 substrate to cope with the challenge. The reflection coefficient response of the structure lies beneath −10 dB reference over the frequency span of 1.3–18.6 GHz for the normally incident electromagnetic waves. The multilayered structure incorporates the entire microwave radar frequency span with a relative fractional bandwidth of 173.86%. Moreover, to examine the applicability of the structure for a nonplanar geometrical surface, we further design the structure on a very thin FR4 substrate that can be bent easily. We performed an RCS analysis of the redesigned structure under monostatic and bistatic conditions. The structure thereby exhibits novelty in terms of wider stealth and electromagnetic compatibility applications and also a good counterbalance among different design attributes comprising thickness, bandwidth, and periodicity, unlike the earlier reported work. The proposed prototypes are fabricated and experimentally validated for planar and curved surfaces, respectively. The experimental results depict a good concurrence with the simulated results.

Coding Engineered Reflector for Wide-Band RCS Reduction Under Wide Angle of Incidence

This communication presents the design of 1 bit coding engineered reflector for wideband monostatic/bistatic radar cross section (RCS) reduction under a wide angle of incidence by redirecting the backscattered electromagnetic (EM) energies into wide and countless angles. The proposed surface can achieve an excellent monostatic/bistatic RCS reduction performance of more than 10 dB over a wide frequency range from 60 to 120 GHz under wide angles of incidence up to 75°. This is achieved by designing a wideband anisotropic polarization rotator unit cell with a relative polarization conversion bandwidth of 66.7% and polarization conversion efficiency of more than 99%. The unit cell and its mirrored version are used to represent the “0” and “1” coding states of an optimized 1 bit coding sequence. The distribution of the “0” and “1” coding states and the dimensions of the anisotropic unit cell are optimized carefully, such that the unit cell will have 180° ± 30° reflection phase difference between the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -axes over the whole three frequency bands (V-, E-, and W-bands) and obtains ultrawideband and wide-angle diffusion scattering patterns under oblique incidence up to 75°. The simulation and experimental results show that the proposed coding engineered reflector has nearly uniform diffusive scattering characteristics under normal and wide-angle off-normal incidences of EM waves up to 75° over the three frequency bands.

Analysis and Design of Wideband Low-RCS Fabry–Perot Antennas With Reduced Profile

In this article, two incomplete partially reflective surface (PRS)-based Fabry–Perot (F-P) antennas each with a high gain, wideband low radar cross section (RCS), and reduced profile are proposed. The reductions of the antenna profiles and RCS are realized based on artificial magnetic conductor (AMC) surfaces and the phase cancellation, respectively. In the first design, two AMC surfaces are placed around the radiation patch and above the PRS. The thickness of the F-P cavity is reduced by half due to the zero-phase reflection of the lower AMC surface around the radiation patch. The income waves are partly reflected by the upper AMC surface above the PRS with zero reflection phase and partly penetrate the PRS and then reflected by the lower AMC surface also with zero reflection phase. The reflected EM waves from the bottom AMC surface travel another distance of quarter wavelength in the upward direction making the total electrical path traveled be half wavelength, thereby causing a phase shift of 180° with the reflected waves from the upper AMC surface, and thus resulting in a wideband RCS reduction. For the second design, another AMC surface is placed below the PRS. On one hand, the middle and lower AMC surfaces have the same reflection phases and then an F-P cavity with a subwavelength thickness is generated. On the other hand, the phase difference between the upper and lower AMC surfaces is also designed as 180°, which is used to suppress the total backward RCS. The two F-P antennas are both fabricated and measured. Measured results validate their reflection, radiation, and scattering performance well. To the best of our knowledge, this work is the first design, which integrates the physical (thin F-P cavity), radiation (gain enhancement), and scattering (broadband RCS reduction) performance of the F-P antenna.

Polarization Converter Surface Integrated MIMO Antenna for Simultaneous Reduction of RCS and Mutual Coupling

This letter provides an effective solution to deal with the radar cross section (RCS) and mutual coupling of the multiple-input–multiple-output (MIMO) antenna simultaneously. A wideband reflective type polarization converter (PC) is designed and its strategic placement in between the antenna elements of the two-element MIMO antenna has been conceived to mitigate these two issues concurrently. The antenna elements of the proposed MIMO antenna are placed at a proximal distance of 0.088 λ from each other. The proposed MIMO architecture ensures a maximum coupling reduction of 46 dB compared to the conventional MIMO across 4.4–8 GHz. The PC surface reduces the reflection of copolarized waves and enhances cross-polarized reflection. A supercell formed by a unit cell of PC and its 90° rotated counterpart causes phase cancellation of cross- polarized reflected waves, which contributes to wideband RCS reduction by a maximum value of 7 dB. The alignment of PC cells in a column between the adjacent antenna elements causes a reduction in the mutual coupling due to introduction of an extra coupling path and cross-polarization conversion. A good agreement between the simulated and measured results validates this concept of the proposed MIMO design with low RCS and mutual coupling.

Extremely Wideband and Omnidirectional RCS Reduction for Wide-Angle Oblique Incidence

In this communication, a novel metasurface with multiple unit cells of different thicknesses based on optimized multielement phase cancellation (OMEPC) is proposed for extremely wideband, omnidirectional, and polarization-independent radar cross section (RCS) reduction under wide-angle oblique incidence. Omnidirectional characteristic refers to the capability of RCS reduction under all azimuth angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi ^{i}$ </tex-math></inline-formula> ) at certain elevation angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta ^{i}$ </tex-math></inline-formula> ). The equivalent circuit model of the square patch unit cell is analyzed under both normal and oblique incidences. Unit cells of multiple thicknesses are adopted to solve the in-phase reflection at certain frequencies. The scattered fields of the proposed multiple-element metasurface under different frequencies, polarizations, and incident angles are jointly optimized and simultaneously suppressed by OMEPC. When the range of incident angles is increased from 0° to 40°, the proposed multiple-element metasurface can achieve the 10 dB specular RCS reduction from 7.34 to 64.85 GHz with a ratio bandwidth of 8.84:1 for both TE and TM polarizations, and the 8 dB RCS reduction bandwidth is approximately 6.76–83.70 GHz. The measurement results are in agreement with the theoretical analysis and simulation results.

Wideband radar cross-section reduction using plasma-based checkerboard metasurface

For stealth technology, in order to overcome the limitations of thin-layer plasma for electromagnetic waves attenuation and further broaden the radar cross-section (RCS) reduction (RCSR) band of the metasurface, the plasma-based checkerboard metasurface composed of plasma and checkerboard metasurface is investigated to achieve better RCSR. We designed a checkerboard metasurface which can achieve abnormal reflection to reduce RCS and whose −10 dB RCSR bandwidth is from 8.1 to 14.5 GHz, the RCSR principle of it lies in the backscattering cancellation, which depends on the phase difference of artificial magnetic conductor (AMC) units. The designed plasma-based checkerboard metasurface is a thin composite structure, including a checkerboard metasurface, a plasma layer, and an air gap which is between them. Full wave simulations confirm that the plasma-based checkerboard metasurface’s ‒10 dB RCS reduction bandwidth and RCS reduction amplitude, are both increased under different polarized waves compared with the only single plasma or the only metasurface. We also introduced the reason and mechanism of the interaction between plasma and the checkerboard metasurface to improve the RCSR effect in detail. As plasma-based checkerboard metasurface does not need the plasma to be too thick for plasma stealth, its application in practical scenarios is easier to implement.

High-Quality Ferromagnet Fe3GeTe2 for High-Efficiency Electromagnetic Wave Absorption and Shielding with Wideband Radar Cross Section Reduction.

A high-quality Fe3GeTe2 single crystal with good electrical, magnetic, and electromagnetic wave absorption and shielding properties was prepared in a large quantity (10 g level) by solid-phase sintering and recrystallization method, which would promote its in-depth research and practical application. It has good room-temperature electrical properties with a mobility of 42 cm2/V·s, a sheet (bulk) carrier concentration of +1.64 × 1018 /cm2 (+3.28 × 1020 /cm3), and a conductivity of 2196.35 S/cm. Also, a Curie temperature of 238 K indicates the high magnetic transition temperature and a paramagnetic Curie temperature of 301 K shows the large ferromagnetic-paramagnetic transition zone induced by the residual short-range ferromagnetic domains. Particularly, Fe3GeTe2 is in a loosely packed state when used as a loss agent; the electromagnetic wave absorption with a reflection loss of -34.7 dB at 3.66 GHz under thin thickness was shown. Meanwhile, the absorption band can be effectively regulated by varying the thickness. Moreover, Fe3GeTe2 in a close-packed state exhibits terahertz shielding values of 75.1 and 103.2 dB at very thin thicknesses of 70 and 380 μm, and the average shielding value is higher than 47 dB, covering the entire bandwidth from 0.1 to 3.0 THz. Furthermore, by using Fe3GeTe2 as a patch, the wideband radar cross-section can be effectively reduced by up to 33 dBsm. Resultantly, Fe3GeTe2 will be a promising candidate in the electromagnetic protection field.

An integrated 2‐bit metasurface array antenna with broadband low radar cross‐section covering large incident angle space

Based on an integrated design of metasurface units and antenna elements, a 2-bit metasurface array antenna with broadband low radar cross-section (RCS) covering large incident angle space is proposed in this study. The slot width's influences on the reflective phase and element radiation performance are analysed. Furthermore, a genetic algorithm is utilised to obtain the coding pattern of the array antenna with diffuse scattering characteristics. A wideband RCS reduction is achieved from 4.2 to 9.0 GHz under x-polarised incidence, and it has oblique incident angle stability ranging from 0° to 60° due to non-uniform element arrangement. The current cancelation phenomenon is found to reveal the RCS reduction mechanism. Besides, the proposed antenna gain is 15.9 dBi with a peak aperture efficiency of up to 90.8%. Experimental results have a close coincidence with the simulations, which verifies the capability of the proposed design.

Wideband RCS Reduction of Microstrip Antenna Array Using Coding Metasurface With LowQResonators and Fast Optimization Method

In this letter, a novel coding metasurface (CM) based on low <i>Q</i> resonators and fast optimization method is proposed to achieve wideband radar cross section (RCS) reduction of the microstrip antenna array (MAA) while maintaining its radiation properties. Theoretical analysis reveals the relationship between the <i>Q</i> value and the phase shift of the resonator, which indicates that the wideband control of the reflected wave can be achieved with the low <i>Q</i> resonator. Moreover, the fast optimization method based on the convolution theorem is proposed, which enhances the optimization efficiency of the coding matrix. Finally, the CM with two kinds of low <i>Q</i> resonators is constructed and applied to the MAA for wideband RCS reduction. The measured results indicate that the proposed low RCS MAA (LRMAA) can realize more than 10 dB RCS reduction in 5.8&#x2013;21.5 GHz, which also demonstrates superior specular scattering suppression. In parallel, the radiation properties of the LRMAA are consistent with those of MAA. The proposed strategy achieves the high integration of radiation and scattering properties, which has potential applications in antenna systems of stealth platforms.