Radar Cross Section Reduction Research Articles

Wideband RCS reduction of microstrip antenna using artificial magnetic conductor metasurface

Wideband RCS reduction of microstrip antenna using artificial magnetic conductor metasurface

Scattering suppression with dual-band single-layer mantle cloak for cylindrical metasurface

This paper investigates scattering suppression with a dual-band and single-layer mantle cloak by using the proper structure for cylindrical objects. The mantle cloak’s surface impedance is calculated according to the Mie Theory to obtain considerable scattering reduction at all angles of the cylinder. The analytical formulation assists in determining the proper unit cell dimensions to obtain design parameters. Firstly, the patch array geometry is applied on the mantle cloak for a single operating frequency with different unit cell numbers. Then a new design of a dual-band single-layer mantle cloak is made with the findings obtained. Simulations are conducted for both mantle cloaks, and bi-static Radar Cross-Section (RCS) analyses are carried out, generating simulated outcomes for cylinders that are both cloaked and uncloaked. The comparison of the scattering suppression between them reveals that the cloaked cylinders demonstrate a significant reduction in scattering. These achievements apply to both single-band and dual-band designs. A novel dual-band single-layer mantle cloak is presented with a new design method and scattering suppression is observed in more than one operating frequency. As evidence of the subject, a dual-band cloaked cylinder is designed with a total radius of 0.13λ0, a total length of 2.59λ0, and a thin dielectric layer’s thickness of 0.0127λ0(λ0i s the wavelength at design frequency f0=3 GHz). This dual-band cloaked cylinder has 7.6 dB absolute RCS reduction at f=2.05 GHz and 5.6 dB absolute RCS reduction at f=3.75 GHz. An efficient scattering suppression is achieved for these two different frequencies in all directions. The considerable degree of invisibility observed in this study opens up possibilities for future investigations in various fields, including radar applications, sensing applications, and antenna isolation for the purpose of blockage reduction.

Architecture Design of a Bamboo Cellulose/Nb2CTx MXene/ZIF-67-Derived Lightweight Co/Nb2CTx/Carbon Aerogel for Highly Efficient Electromagnetic Wave Absorption, Thermal Insulation, and Flame Retardant

Designing biomass-derived carbon-based lightweight electromagnetic wave (EMW) absorbers with multiple functions is promising research. However, the design of carbon-based EMW absorbers with multifunctionality for practical application remains a substantial challenge. Herein, a porous architecture engineering strategy was used to prepare a high-performance EMW absorption composite material with thermal insulation and flame-retardant properties The multifunctional Co/Nb2CTx/carbon aerogel with porous architecture composed of a bamboo-derived carbon aerogel, two-dimensional (2D) Nb2CTx, and ZIF-67-derived Co nanoparticles was prepared. Bamboo cellulose and few-layered Nb2CTx MXene constructed the three-dimensional (3D) aerogel architecture, ZIF-67 was then uniformly anchored on the aerogel skeleton through chemical deposition, and the Co/Nb2CTx/carbon aerogel was finally prepared by pyrolysis. The 3D interconnected network heterostructure not only contributes to conduction loss but also prolongs multiple reflection and scattering paths of EMW, which can improve the dielectric loss. Nb2CTx and Co nanoparticles play an important part in modulating the impedance matching and promoting the EMW attenuation ability due to the plenty of dipole/interfacial polarization loss and supplementary magnetic loss. The obtained Co/Nb2CTx/carbon aerogel possesses low density (54.03 mg cm–3) and achieves excellent reflection loss and broad effective absorption bandwidth (−60.25 dB and 4 GHz, respectively) at an ultrathin thickness of 1.67 mm with an ultralow filling content of 10 wt %. The radar cross section (RCS) reduction value can reach 31.24 dB m–2, indicating that the absorber can effectively reduce the probability of the target being detected by the radar detector. The strategy of porous architecture engineering provides guidance for the design of biomass-based electromagnetic wave absorption materials with thermal insulation property and flame-retardant capacity.

Multi-objective shape optimization of doubly offset serpentine diffuser using Adjoint method

Doubly offset serpentine diffusers are needed in the compact designs of modern stealth fighters with highly integrated propulsion systems. In addition, these doubly offset serpentine diffusers are also essential to provide reduced radar cross-section (RCS) due to the blockage of a complete line of sight. In this research, shape optimization of the doubly offset serpentine diffuser is achieved using a multi-objective approach to maximize the pressure recovery (PR) and minimize the flow swirl angle (α) and distortion coefficient (DC) at the aerodynamic interface plane (AIP). A computationally efficient Adjoint-based method was implemented for the optimization. For baseline geometry, an additional offset is added to NASA’s M2129 single serpentine duct to make it doubly offset serpentine diffusers. The freeform deformation technique was used to parametrize the baseline shape using 180 control points. A steady-state flow solution through the diffuser was achieved by solving Reynolds-Averaged Navier-Stokes (RANS) equations using a general-purpose computational analysis tool, i.e., ANSYS Fluent. The sensitivity of objective functions from the Adjoint solver was used to compute the required design change in the direction of minima or maxima of the objective functions using the steepest descent optimization technique. Subsequently, the calculated design changes were implemented through mesh Morpher. The Adjoint-based approach and freeform deformation resulted in a powerful and efficient optimization framework. The optimized shape showed a significant reduction in distortion coefficient and flow swirl angle, along with a slight increase in pressure recovery.

Multiband polarization insensitive metamaterial absorber for radar cross-section reduction

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands.

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°.

Multiple-Beam Steering Using Graphene-Based Coding Metasurfaces.

Recently, the coding metasurface has gained significant attention due to its exceptional potential in controlling electromagnetic (EM) waves with the rapid development of wireless communication systems. Meanwhile, graphene shows tremendous promise for the implementation of reconfigurable antennas due to its high tunable conductivity and its unique property that makes it a very suitable material for realizing steerable coded states. In this paper, we first propose a simple structured beam reconfigurable millimeter wave (MMW) antenna using a novel graphene-based coding metasurface (GBCM). Different from the previous method, its coding state can be manipulated by altering the sheet impedance of graphene instead of bias voltage. Then, we design and simulate several most popular coding sequences, including dual-, quad-and single-beam-generated implement, 30° beam deflection, as well as a random coding sequence for radar cross-section (RCS) reduction. The theoretical and simulation results show that graphene has great potential for MMW manipulation applications, which lay a foundation for the subsequent development and fabrication of GBCM.

Ultra-broadband electromagnetic wave absorbent: In-situ generated silica modified conductive carbon fiber aerogels

The research and development of dielectric microwave absorbing materials with broad electromagnetic (EM) response is a significant project in EM wave absorption field. To achieve high-performance absorption and strong interfacial bonding at the same time, thermal-assisted in-situ bonding technology was applied to fabricating the dielectric composite absorbing materials. Thanks to the combination of vacuum filtration and in-situ hydrothermal reaction, the as-prepared binary composite aerogel shows both strong interface contacting and good mechanical stability. In addition, the carbon nanofibers/silica composite aerogel (CSA) exhibits ultra-broad effective bandwidth covering from S to Ku band, originated from the uniform dispersed silica aerogel in conductive carbon fiber network. In details, for CSA1 sample, the maximum reflection loss (RL) values and effective absorption bandwidth reach −46.2 dB (1.8 mm) and 5.2 GHz (1.5 mm). Meanwhile, the optimum RCS reduction values reaches 16.2 dB m2 when the detection theta was set as 0°. For CSA2 sample, the effective absorption bandwidth reaches 8.64 GHz at 1.5 mm, and tends to possess lower frequency EM response covering the S-band. This work exhibits a kind of broad-bandwidth aerogel absorbers at low thickness, which shows huge potential in large-scale production of microwave absorbing devices.

Ion-exchange reaction construction of carbon nanotube-modified CoNi@MoO2/C composite for ultra-intense and broad electromagnetic wave absorption

Structural design and composition adjustment are promising approaches for the preparation of lightweight absorbers with high absorption performance and low matching thickness. In this work, a carbon nanotube-modified CoNi@MoO2/C composite was synthesized by ion-exchange, in-situ growth, and pyrolysis methods. For the synthesized CoNi@CNTs@ MoO2/C composite, the minimum reflection loss value (RLmin) was −63.2 dB at a thickness of 2.3 mm, and the effective absorption bandwidth reached 8.8 GHz (9.2–18 GHz) at a thickness of 2.5 mm. The potential microwave absorption mechanism is attributed to the synergistic effects of polarization relaxation, electron transmission, ferromagnetic resonance, as well as multiple reflections and scattering in the hierarchical nanocomposite. In addition, the radar cross-section (RCS) attenuation was calculated via HFSS to analyze the EMW absorption capacity in the actual far field. The RCS reduction was 36 dB m2 for a scattering angle of 0°. Overall, this work provides theoretical support for the controlled growth of metal-catalyzed CNTs and presents an effective guide for optimizing the electromagnetic and absorption performances of MA materials.

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.

A review: Advancement in metamaterial based RF and microwave absorbers

Microwave absorbers (MAs) are specially designed structures which dissipate an incident electromagnetic (EM) wave by converting it into thermal energy and thereby prevents reflection and/ or transmission. The MAs are extensively in demand due to their property to reduce the electromagnetic wave interference (EMI) and to enhance electromagnetic shielding (EMS). MAs are also used in potential military applications as a stealth technology to design stealth aircrafts, warships and army clothing etc. due to the reduction of radar cross section (RCS) of the defense equipment by the absorber coating. In this review work, study of metamaterial-based MAs, their characteristics viz. left-handed material property, permittivity and permeability have been discussed in detail. Metamaterials (MMs) or artificial materials that play a significant role in reducing the size and thickness of MAs depending upon the frequency of operation. In this work, theoretical background of MM-based absorbers detailing the effect of permittivity and permeability on absorber performance has also been discussed. Different applications of absorbers are elaborately covered in this paper. Furthermore, frequency selective surface (FSS) which is a two-dimensional array has the capability to reflect or transmit EM wave completely or partially depending upon the nature of FSS. Therefore, distinct categories of FSS-based absorbers are discussed according to the frequency of operation, bandwidth and material specification where the effect of different design parameters is also critically analyzed. The objective of this review paper is to provide an exhaustive study of the unique attributes of MAs having a diverse range of applications for frequencies ranging from microwave, terahertz upto optical frequency domain. This review paper is certainly a vital tool for researchers to accurately understand, explore and work on MA design and selection as per user defined specific frequency and applications.

Homogeneous Two-Layer Structures for Broadband and Wide-Angle RCS Reduction

A two-layer stacked resonance absorber is proposed to achieve broadband and wide-angle radar cross section reduction. The most prominent structure feature is its simple geometry, which comprises two homogeneous dielectric slabs only. The two slab heights are chosen as one-sixth of a guided wavelength to form a three-way cancellation mode via interface reflections while a high permittivity dielectric is used to achieve low profile. The total thickness is less than 0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda_{L}$</tex-math></inline-formula> . Because it involves no periodic structure, both monostatic and bistatic scattering levels can be suppressed in a broad frequency band and a wide angular region. A bouncing ray-based high frequency method was developed to perform parametric studies and design optimization in a timely fashion. Measured and simulated results are compared in spectral and angular domains. An 83% 10 dB RCS reduction band is observed. More than 10 dB back scattering suppression is achieved up to ±75° from the surface's normal.

Planar polarization rotation reflective surface for X-band RCS reduction in microstrip patch antenna

In this study, a rectangular microstrip patch antenna (MSPA) with a low X-band radar cross section (RCS) is proposed. The existing RCS reduction involves many layers, which raises design complexity. The research challenge is to lower the X-band RCS of a patch antenna using single-layer while keeping the good radiation performance. A polarization rotation reflective surface (PRRS) made up of unit cells arranged in the same plane encircles the proposed MSPA. This MSPA's radiation pattern and scattering capabilities are investigated and the effective RCS reduction in the X-band frequency from 8 to 12 GHz is achieved by arranging the unit cells of the newly developed PRRS. The proposed MSPA, which has an impedance bandwidth (BW) of 8.98 GHz to 10.99 GHz and a low X-band RCS, eliminates the requirement for multiple layers in the antenna. In addition, the antenna has the length and width of 23 mm and 41 mm with 14 unit cells and radiating elements of antenna is 9 mm x 6 mm and the substrate have the thickness of h = 2 mm.

A Low-Scattering Antenna Array at Both Normal and Grazing Incidence

In this paper, we investigate a low-scattering antenna array consisting of two different low radar cross-section (RCS) antenna elements. The low-scattering performance is achieved by broadband in-band absorbing with x (TM)-polarization and phase cancellation with y (TE)-polarization at normal incidence and a special shape design at grazing incidence. We demonstrate the effectiveness of the proposed antenna array through simulations and measurements. Compared with the reference one, the results show that it can achieve remarkable wideband monostatic RCS reduction from 3.3 to 8 GHz with a maximum reduction value of 23.5 dB at normal incidence and from 4.4 to 12.5 GHz with a peak reduction value of 15.3 dB at grazing incidence. Moreover, a low-RCS carrier is codesigned with the antenna array to verify the low-scattering property, which indicates that the proposed antenna array has a great potential for use in various application scenarios.

Manipulation of nano-metals to implement rational conduction tailoring for high-efficiency microwave absorption

Conduction tailoring (CTs) of dielectric absorbers has already been regarded an effective strategy to realize the controllable electromagnetic (EM) wave response. However, there is still lacking of elaborate understanding of the relationship between the design of CTs and microscopic properties, as well as how they relate to EM wave absorption. Here, reduction graphene oxide-based CTs is developed by nano-metal intercalation into RGO lamella via additive-assisted vacuum filtration assembly technique and in-situ metal reduction technique. After the integration of micro-/macro-evolution of composition and structure, cross-scale analog computation, and EM patterns/power loss analysis, for the first time the implementing mechanisms of CTs on the improvement of EM wave absorption properties have been acquired. Benefiting from the balance between the energy capture and EM energy transformation, effective frequency bandwidth of 6.9 GHz at 2.2 mm and 5.2 GHz at 1.8 mm can be achieved after the CTs design by silver and copper. Meanwhile, the optimum RCS reduction values reach 2.29 dB m2 when the detection theta was set as 20°. This work systematically explores the CTs-based relation chains of charges-composition-models-EM patterns, which is of great importance for the optimization of effective operating bandwidth and reflection loss properties.

Bistatic RCS reduction caused by radionuclide layer for spherical object

Radar cross section (RCS) is one of the important research topics in recent decades and the use of Radionuclide Layer (RNL) is one of the methods for radar cross section reduction. In this paper, the RNL of Americium-241 is considered on the surface of the spherical body with a radius of 5 cm. The range of alpha particles emitted from RNL and the electron density of air at standard temperature and pressure (STP) conditions have been extracted by the SRIM and Geant4 computational codes. Finally using CST software and RF module, the radar cross-section of the conductive spherical body, without and with plasma induced by RNL are obtained in different activities. The radar cross-section reduction of about for the spherical body in the frequency range of 2 to 12 GHz is observed for the activity of .

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.

A Highly Efficient Method for Designing Bisymmetric P‐B Phase Element Patterns of Coding Metasurfaces

AbstractThe conventional trial‐and‐error method employed in the element pattern design of coding metasurfaces lacks theoretical guidance and requires considerable time and computational resources. To overcome this problem, this paper proposes a highly efficient design method for bisymmetric Pancharatnam‐Berry (P‐B) phase element patterns. First, the equivalent impedances of the element patterns are derived from the expected reflectance and frequency range using the transmission matrix method. Subsequently, the optimal geometric parameters of the element patterns are obtained using the equivalent circuit model. For the same element pattern, the time consumption is reduced by more than 25 times compared with that required for a single full‐wave simulation. The simulation results show that metasurfaces adopting various design element patterns and the same coding sequence exhibit excellent backscattering energy homogenization performance, with a radar‐cross‐section reduction (RCSR) of less than −10 dB in the 9.47–17.57 GHz band. Two types of metasurfaces are fabricated using a meshed pattern, a sodium–calcium glass and a metallic mesh. The measured RCSR is less than −10 dB for a broadband of 7.74 GHz, and the normalized optical transmittance is 85% within 380–2500 nm, which is favorable for optical windows used in aerospace, medical, and precision instrumentation.

Ternary RCS reduction metasurface based on a parallel resonance circuit

Ternary RCS reduction metasurface based on a parallel resonance circuit

Compact wideband FSS-absorber-based low-RCS reflectarray antenna

This paper presents a method to realize compact broadband low-RCS ReflectArray (RA) antenna based on a Frequency Selective Surface (FSS) absorber and a reflective metasurface. Such an FSS absorber consists of a resistance-loaded lossy layer and an FSS layer, which is utilized to reach an absorption-transmission response. The bottom reflective metasurface works as a phase array, reshaping the quasi-sphere wave from the feeding antenna into the quasi-plane wave. As a demonstration, the low-RCS RA antenna is simulated, fabricated, and measured. The simulated and measured results show that the developed low-RCS RA antenna has an aperture efficiency of 42.7% and a gain of 25.4 dBi in the X band. In the meantime, it simultaneously reaches the 10 dB RCS reduction for the orthogonal polarizations at the S and C bands, corresponding to a fractal bandwidth of 120%. Specifically, the adopted patch-feeding antenna makes the RA antenna more compact than the horn-feed conventional ones. Furthermore, the proposed RA antenna uses a few layers of substrates, making it lower in cost and easier for fabrication. The proposed design may have potential application in integrated stealth communication systems.