Radar Cross Section Reduction Research Articles

1-Bit Reconfigurable Transmitarray Antenna with Out-of-Band RCS Reduction

Stealth reconfigurable transmitarray antennas (RTAs) are essential components in wireless communication and radar detection systems. Therefore, in this study, we propose a 1-bit RTA with out-of-band radar cross-section (RCS) reduction. The antenna consists of an absorptive frequency selective transmission (AFST) layer and RTA layer separated by air. Specifically, the AFST layer achieves out-of-band RCS reduction and in-band transmission utilizing the first three resonant modes of a bent metallic strip with a centrally loaded resistor. Meanwhile, the RTA layer adopts a receiver–transmitter structure with an active receiving dipole and a passive orthogonal transmitting dipole. 1-bit phase shift is achieved by alternating two pin diodes integrated on the active dipole to reverse its current direction. To evaluate the proposed design, a 16 × 16-element prototype was designed, fabricated, and measured. For scattering, the bandwidth of 10 dB RCS reduction was about 52.5% and 43.8%, respectively. For radiation, the measured gain was 20.1 dBi at 7.5 GHz, corresponding to an aperture efficiency of 12.7%. The gain loss of beam scans to ±60° was about 5 dB in both two principal planes.

A butterfly metasurface with efficient multi-functional polarization conversion operating in the Ku-Ka band

A highly efficient and multi-functional butterfly polarization conversion metasurface is proposed for the Ku-Ka frequency range, designed to reduce the radar cross-section. The suggested converter enables dual frequency bands linear-to-cross (LX) and linear-to-circular (LC) polarization transformations. The efficiency of cross-polarization conversion exceeds 90% over the frequency ranges of 14.57–16.30 GHz and 25.70–37.03 GHz, with relative bandwidths of 11% and 36%, respectively. Reflections of left-hand (LHCP) and right-hand circularly polarized (RHCP) waves are realized within the frequency ranges of 17.78–25.31 GHz and 37.38–37.73 GHz, with relative bandwidths of 35% and 0.9%. The oblique incidence significantly affects the metasurface conversion performance, and the proposed model manifests angular robustness up to 60°. Additionally, the butterfly metasurfaces are deployed in a triangular chessboard configuration to achieve radar cross section (RCS) reduction spanning the frequency bands of 14–15.17 GHz, 24.60–35.20 GHz, and 36.30–38 GHz. Drawing from simulation results and test-based validation data, the proposed converter holds promising applications in wireless communication, antenna engineering, and radar stealth.

Angle of Attack Effects on the Induced Structural Loads of a Weapons Bay

AbstractAero-acoustic analysis was conducted on a weapons bay numerical model with doors, incorporating radar cross section reduction features. The effect of the angle of attack on the aero-acoustic response of the cavity was analysed at Mach numbers of 0.85 and 1.20. It was found that incidence influenced both mean-flow features and acoustic response. Further, linear and angular accelerations induced by the flow on the bay doors revealed potential adverse fluid–structure coupling when the results were compared with modal analysis. Again, the angle of attack did influence the aeroacoustic effects on the cavity door structure.

Study on Novel Radar Absorbing Grilles of Aircraft Engine Inlet Based on Metasurface Design Theory

In modern warfare, the advancement of low detectable technology has made the reduction of an aircraft radar cross section (RCS) crucial for survivability, while engine inlets significantly impact the overall detectability index as major forward scattering sources. Inspired by radar absorbing structures (RASs) based on metasurface theory, as well as the spoof surface plasmon polariton (SSPP) theory, this paper proposes a comprehensive design of radar absorbing grilles (RAGs) which are installed at the inlet aperture of the aircraft intake, where RAGs allow airflow to cross through and absorb the detecting radar wave. To enhance the ability of electromagnetic wave attenuation, an indium tin oxide (ITO) film is added in the middle of the RAGs to change the impedance characteristics. This study clarifies the mechanism influencing radar wave absorption characteristics through design parameters (unit length and sheet resistance) and radar characteristic parameters (frequency, incident angle, and polarization mode). The absorption peak gradually shifts towards lower frequencies with the increase in unit length from 8 to 16 mm of the grille. The integrated average absorption first increases and then decreases with the increase in sheet resistance from 100 to 800 Ω/□ applied as ITO film in the middle of the grille. When the unit length of RAG is 12 mm and 400 Ω/□, the sheet resistance is applied, and a 90% absorption bandwidth is achieved to 100% within the 8–18 GHz band. The 90% absorption bandwidth reaches 72.3% in the 2–18 GHz band while maintaining absorption above 40% in the 2–8 GHz band. The integrated average absorption reaches 0.887, and the 90% absorption bandwidth increases to 255.6% of the original model’s bandwidth. The results indicate that the proposed RAGs based on metasurface exhibit broadband absorption performance and high angular stability, providing technical support for further application of these grilles in aircraft engine inlets.

Achieving Broadband RCS Reduction on Curved Surfaces through Gradient Unit Design and Partition Layout Strategy

Novel metastructure designs can efficiently manipulate electromagnetic responses. However, achieving exceptional electromagnetic manipulation capabilities in conformal states remains challenging. Herein, we proposed an innovative method that integrates gradient units with the partition layout strategy to facilitate broadband radar cross section (RCS) reduction under different curvatures. The proposed metastructure demonstrates broadband impedance matching characteristics through a gradient multi-layer design and exhibits strong adaptability to complex structures owing to the application of additive manufacturing technology. It demonstrates a remarkable -10 dB RCS reduction across a wide frequency bandwidth of 5.4–18 GHz in its planar state by integrating the micro-material composition and macro-geometry design while maintaining RCS reduction within the central angle range up to 90°. This paper presents a straightforward and innovative approach for constructing conformal metastructures, highlighting their potential applications in both military and civilian domains.

Ultra-wide band and high efficient Polarization converting metasurface employing Bell-shaped unit cell for RCS reduction

Polarization is a dominant parameter regarding communication systems in recent times. The standard polarization techniques can be used only to a certain extent because of their huge size and limited bandwidth constraints. A design of bell-shaped polarization converting metasurface (PCMS) is presented in this paper which is highly efficient for Radar cross section (RCS reduction) and also operates in ultra-wideband. The designed PCMS attains a polarization conversion ratio of more than 90% by demonstrating the transformation of the linear polarization wave to its orthogonal counterpart. The PCMS is arranged in a triangular chessboard configuration to reduce the RCS. RCS reduction is obtained by achieving destructive interference, accomplished by two unit cells. The two unit cells, PCMS and its mirror will have a phase difference of 180 ± 37°. The phase cancellation is obtained by rotating and arranging the proposed PCMS at 90°, 180° and 270°. RCS reduction is obtained in a frequency range from 4 GHz to 24.8 GHz with 144% FBW. This PCMS is verified experimentally. A good agreement is found between the simulation and the experimental results.

Lightweight dielectric-magnetic synergistic necklace-shaped Co@NCP/carbon nanofiber composites for enhanced electromagnetic wave absorption

In order to solve the problem of impedance mismatch of carbon fiber absorbing materials, it is crucial to create a carbon-based absorbing material with a special structure, synergistic magnetic and dielectric properties. In this paper, necklace-shaped Co@N-doped carbon polyhedron /carbon nanofiber (Co@NCP/CNF) composites with synergistic magnetic and dielectric properties are successfully fabricated by electrospinning. Compared with Co@NCP and CNF, the optimal minimum reflection loss of Co@NCP/CNF composite is -66.14 dB at 2.89 mm and the maximum effective absorption bandwidth is 6.24 GHz (11.76-18.00 GHz) at 2.25 mm at a low filler load of 10 wt.%. The necklace-like structure, the coupling effect of dielectric and magnetic materials and the heterogeneous interface form multiple polarizations, conductive losses and multiple loss mechanisms to optimize impedance matching and attenuation performance, which is conducive to excellent absorption performance. More importantly, the radar cross section (RCS) reduction is as high as 24.02 dB·m2, which has proven to have a good absorption effect in actual application environments. This work combines the advantages of Co@NCP and CNF very well, which provides guidance for designing EM waves nanocomposite fiber absorbers with lightweight and strong absorbing properties.

One-Click to 3D: Helical Carbon Nanotube-Mediated MXene Hierarchical Aerogel with Layer Spacing Engineering for Broadband Electromagnetic Wave Absorption.

MXenes are 2D materials known for their unique electromagnetic wave absorption (EMWA) properties arising from their varied composition and structure. In this study, a one-step ice-assisted process is utilized to directly transform 2D MXene into 3D single-layer MXene aerogels (SMAs). Furthermore, the interlayer spacing of the SMAs is optimized by incorporating helical carbon nanotubes (HCNTs). Because of the van der Waals interaction between the MXene nanosheets and HCNTs, the assembled HCNT@MXene aerogels (HMAs) exhibited a regular porous structure and moderate conductivity, leading to significantly enhanced electromagnetic responses, as demonstrated by finite element simulation. The HMAs showed an exceptional EMWA, with a minimum reflection loss of -51.45 dB and an effective absorption bandwidth of 6.48 GHz at 3.0 wt.% filler ratio. Additionally, visualization of surface charge distribution and power loss density characteristics clarified the underlying EMWA mechanisms. By employing a hollow structure gradient metamaterial design, the effective EMWA bandwidth is further expanded to 13.98 GHz. Additionally, HMAs exhibited the maximum radar cross-section reduction values with 27.08 dBm2. Moreover, the HMAs exhibited excellent thermal insulation capability. This paper presents a straightforward yet effective method for fabricating MXene aerogels and offers valuable insights for the development and application of MXene-aerogel-based EMW absorbers.

Hierarchically structured composite with 3D interlocking architecture for multi-band defense

The development of high-performance electromagnetic wave absorbing (EMWA) materials for radar stealth applications poses a persistent challenge, particularly when addressing the demanding requirements of diverse frequency bands in increasingly complex and dynamic environments. Precisely tailoring the microstructure of these materials presents a powerful strategy for achieving multifunctional integration and unlocking new possibilities for practical applications. In this work, we present a novel hierarchically structured composite foam with 3D interlocking architecture, fabricated through a straightforward foaming and calcination process. It features a unique dual three-dimensional continuous phase structure that facilitates the formation of an efficient conductive network, promoting free electron mobility and enhancing polarization loss. The composite demonstrates exceptional EMWA performance, exhibiting a wide effective absorption bandwidth (EAB) of 6.1 GHz and a remarkable absorption intensity of -63.2 dB along with RCS reduction value up to 28.7 dB m2. Furthermore, the composite illustrated strong infrared stealth properties and efficient photothermal conversion abilities. When heated to 56°C, its surface temperature only increased by 4°C in 10 minutes. Under direct sunlight, its surface temperature rose from 21°C to 71°C in just 6 minutes. Lightweight, flexible, and adaptable to diverse environmental conditions, the HCC composite holds significant promise as a multi-spectrum defense material. Its versatility makes it an ideal candidate for integration into a wide range of equipment, clothing, and wearable technologies, offering advanced capabilities for radar, infrared, and visible light signature reduction.

On Intake–Compressor Interactions Within an Integrated Propulsion System

Abstract The integration of a propulsion system into the airframe can contribute to the overall aircraft performance and is beneficial for military applications due to a reduction of the aircraft radar cross section. On the other hand, engine integration calls for serpentine engine intake systems in which generally combined pressure-swirl distortions are provoked, which affect the performance of the propulsion system. The military engine intake research duct was designed to provoke a large-scale flow separation as well as a combined pressure-swirl distortion. The serpentine research duct is tested in both a remote- and close-coupled setup with the Larzac 04 turbofan engine to assess the aerodynamic interactions between the flow within the intake duct and the compression system. The upstream effect of the compression system on the steady-state duct flow is within the range of expectations. Less is known from the open literature with regard to the unsteady character of the flow in such a setup. Three distinct unsteady flow phenomena caused by the serpentine shape of the duct are identified up- and downstream of the low pressure compressor in the remote-coupled setup. An additional distinct low frequency unsteadiness is provoked with a configuration which features vortex generators for flow control. All phenomena are largely attenuated by the upstream effect of the compressor in the close-coupled setup. Nonetheless, the surge margin is massively reduced due to the inflow distortion and stall cells within the first stage of the low pressure compressor are visualized at high thrust settings of both the remote- and close-coupled setup, which are expected to impact the durability of the compression system.

Rare earth doped magnetoelectric composites for enhanced electromagnetic wave absorption

Magnetoelectric electromagnetic wave absorption materials (EWAMs) with multiple loss mechanisms have shown remarkable results in solving electromagnetic (EM) interference and radar stealth. However, due to the Snoek limit, the magnetic properties are affected to some extent. Hence, based on low-cost two-dimensional graphite nanosheets and magnetic ferrite, a rare-earth doping strategy is innovatively proposed, aiming to develop a high-efficiency EWAM. Specifically, taking advantage of the significant differences in magnetic moments and dimensions between Gd and Fe ion, the modified ferrite owns unusual magnetic properties and dielectric capacity. Further, direct control of the EM parameters is achieved by finely tuning the component ratio, which in turn optimizes the response characteristics of EM wave absorption. Experimental results show a maximum reflection loss of −64.04 dB and a wide effective absorption bandwidth covering 4.88 GHz, corresponding to the absorption efficiency of −42.7 dB/mm and 3.25 GHz/mm, respectively. The outstanding performance is related to the synergistic effect of multiple loss management and impedance matching, and further confirmed by the radar cross section (RCS) reduction of 29.15 dBsm. Thus, the novel way opens a new horizon for the next magnetic-based EWAMs.

A facile strategy for customizing multifunctional magnetic‑dielectric carbon microflower superstructures deposited with carbon nanotubes

The novel fabrication of multiple components and unique heterostructure can inject infinite vitality into the electromagnetic wave (EMW) attenuation field. Herein, through the self-assembly of polyimide complexes and catalytic chemical vapor deposition, porous carbon microflowers were synthesized accompanied by carbon nanotubes (CNTs). By regulating the metal ions, the composition and structure of the as-obtained hybrids are modified correspondingly, and thus the adjustable thermal management and EMW absorption capabilities are obtained. In detail, the rich pores and huge specific surface area endow the hierarchical structures with distinguished thermal insulation ability (λ<0.07). The carbon framework and CNTs are beneficial for consuming EMWs via conductive loss and defect polarization loss while reducing the filling ratio and thickness. The doped heteroatoms and abundant heterointerfaces generate ample dipole polarization and interface polarization losses (supported by DFT calculation). The metal nanoparticles uniformly embedded in the carbon framework offer optimized impedance matching, proper defect polarization, and suitable magnetic loss. Accordingly, the synergy of magnetic-dielectric balance and flower-like superstructure enables FNCFN2 and NNCFN2 to accomplish remarkable microwave absorbing capacity with thin thickness (14 wt.%). Therefore, respectable specific reflection loss and specific effective absorption bandwidth are acquired (215.39 dB mm–1 and 22.10 GHz mm–1, 257.23 dB mm–1 and 22.12 GHz mm–1 respectively), superior to those of certain renowned carbon-based absorbers. The simulation results of electric field intensity distributions, power loss density, and radar cross section reduction (maximum value of 36.02 dBm2) also verify the prominent radar stealth capability. Moreover, the customizable approach can be applied to other metals to obtain fulfilling behaviors. Henceforth, this work provides profound insights into the relationship between structure and performance, and proposes an efficient path for mass-producing multifunctional and high-performance EMW absorbers with excellent thermal properties.

Efficient polarization conversion metasurface for scattered beam control and RCS reduction

This study proposes and experimentally validates a multifunctional, ultra-wideband polarization conversion metasurface. The design integrates polarization conversion and electromagnetic scattering functions into a single structure, enabling applications in polarization conversion, beam control, and effective reduction of the radar cross-section (RCS). The metasurface achieves linear-to-circular polarization conversion with an axial ratio (AR) of less than 3 dB across dual-band ranges of 14.6–26.8 GHz and 31–33.5 GHz. Additionally, by adjusting metallic resonant rings within the unit structure, cross-polarization conversion with a polarization conversion ratio (PCR) greater than 0.9 is realized in the 13.6–29.8 GHz frequency range, maintaining excellent stability even at oblique incidence angles up to 50°. Leveraging the phase cancellation principle, various coding arrays are designed to precisely control the scattered beams, reducing the RCS by more than 10 dB. The comparison of simulation and experimental results further validates the wide application potential of this polarization converter in fields such as wireless communication, antenna engineering, and radar stealth.

Surface Impedance Modulation of FSS Composite Absorber for RCS Reduction at Normal and Grazing Incidence

Surface Impedance Modulation of FSS Composite Absorber for RCS Reduction at Normal and Grazing Incidence

Low-profile, wideband RCS-reduction antenna array based on a metal-ink hybrid metasurface.

In this study, a highly flexible metal-ink hybrid metasurface that can be integrated with planar structures is proposed. The metasurface achieves wideband absorption performance while maintaining an efficient transmission window. Based on equivalent circuit model analysis, an aperture-coupled antenna array was integrated with the metasurface, enabling simultaneous wideband radar cross-section (RCS) reduction and high-performance radiation. The integration of the metasurface and antenna array allowed the overall structure to maintain a low profile. Simulation results show that the proposed array achieves a 10 dB RCS reduction against a metal plate of the same size over the [2.03, 8.11] GHz range, with a fractional bandwidth of 119.9% under x-polarized wave incidence. Under y-polarized wave incidence, a 10 dB RCS reduction is achieved at both [2.12, 5.1] GHz and [6.1, 8.06] GHz, with fractional bandwidths of 82.5% and 27.6%, respectively. Moreover, the array maintains a peak gain of 26.3 dBi and sidelobe levels less than -18 dB. The experimental results align well with the simulated results. The proposed low-RCS antenna array offers potential advancements in planar antenna technology, enhancing stealth capabilities.

Anisotropic hypocycloid inspired 3-bit digital coding metasurface for radar cross section reduction

Abstract Recently, researchers have realized various exotic electromagnetic control devices using the coded metasurfaces, sparking a broad investigation into the phase or amplitude-based encoding method, as well as their combination, in the field of metasurface design. In this paper, to evaluate the influence of random mutual coupling between the adjacent element on the scattering performance of metasurface, and also to minimize the backward radar cross section (RCS) of metal plate targets, a novel encoding approach combining the reflection phase and element-form has been proposed. During the implementation process, an anisotropic hypocycloid inspired 3-bit digital coding metasurface was designed. It consists of 9 different element-forms, with each capable of providing 7 phase states. Simulation results demonstrate that the random mutual coupling introduced by the proposed elements does not significantly affect the RCS performance of the metasurface. With a good polarization insensitivity property for both linearly and circularly polarized waves, the designed 3-bit digital coding metasurface can achieve more than 20 dB RCS reduction at 10 GHz, while simultaneously transmitting additional information by encoding the element forms. The good consistency between theoretical simulation and sample testing unequivocally validates the precision of the design, this paper may serve as a useful reference for expanding the design methods of metasurfaces.

Bamboo-Based Carbon/Co/CoO Heterojunction Structures Based on a Multi-Layer Periodic Matrix Array Can Be Used for Efficient Electromagnetic Attenuation.

With the popularization of wireless communication, radar, and electronic devices, the hidden harm of electromagnetic radiation is becoming increasingly serious. The design of green biomass carbon-based interface heterojunctions based on lightweight porous materials can effectively protect against electromagnetic radiation hazards. In this work, we constructed an anisotropic heterojunction interface with magnetic and dielectric coupling based on a honeycomb-like periodic matrix multi-layer array repeating unit. The removal of lignin components from bamboo through oxidation enriches the impregnation pores and uniform adsorption sites of the magnetic medium. Further, in situ pyrolysis promotes the formation of a large number of electric dipoles at the interface between the magnetic medium and dielectric coupling inside the periodic cell carbon skeleton, enhancing interface polarization and relaxation. Local carrier traps and uneven electromagnetic density enhance dielectric and hysteresis losses, resulting in excellent impedance matching. Therefore, the obtained bamboo-based carbon multiphase composite absorbent has satisfactory electromagnetic loss characteristics. At a thickness of 1.55 mm, the effective absorption bandwidth reaches 5.1 GHz, and the minimum reflection loss (RL) value reaches -54.7 dB. In addition, the far-field radar simulation results show that the sample has an excellent RCS (radar cross-section) reduction of 33.3 dB·m2. This work provides new directions for the diversified development of green biomass and the optimization of the design of magnetic and dielectric coupling in periodic array structures.

The Effect of the Wall Thickness of the Material Loaded Cavity On the RCS Reduction

In this paper, the effect of a parallel plate waveguide's wall thickness on radar cross-section reduction (RCS) is rigorously analyzed for H-polarization by using the Wiener-Hopf Technique, when the waveguide region is loaded with dielectric material and terminated with a perfect electric conductor (PEC) plate. Transfer matrices are incorporated into the analysis to account for the effect of different material layers through continuity relations. The Fourier transforms of the diffracted field and the boundary conditions yield a modified scalar Wiener-Hopf equation of the second kind (MWHE-2). The classical procedure to solve the MWHE-2 is applied and the approximate expression of the diffracted far field is obtained. Numerical results are given by comparing with the results available in the literature for the case of the wall thickness of the cavity not being considered.

Broadband 3-bit coding metasurface antenna with integrated radiation and scattering performance.

This paper presents the design of an integrated metasurface antenna, which combines a central radiating patch with a quadru-arc (QAS) structure. The metasurface antenna simultaneously achieves high-gain radiation and complex scattering functionality. The modulation of the radiation function is primarily achieved through phase manipulation of the power division feed network, while modulation of the X-polarization scattering function is mainly accomplished by adjusting the arc of the QAS. The effectiveness of this design is verified by designing two metasurface antennas with distinct functionalities. The feed network phases are arranged in a checkerboard pattern in the first approach, resulting in four-beam radiation with a gain of 16 dBi per beam. Additionally, the scattering component utilizes eight scattering structures with a phase difference of 45 degrees to form a 3-bit coding, enabling vortex beam scattering. The second configuration arranges the feed network in phase with the deflected beam, resulting in a deflected beam radiation pattern characterized by a gain of 22.3 dBi. The scattering function is optimized using a simulated annealing-genetic algorithm for phase alignment, resulting in the achievement of RCS reduction across a wide bandwidth range of 8-24 GHz. The proposed metasurface antenna is ultimately fabricated and subjected to rigorous measurements.

Gradient metasurface covered with water-based channels for reconfigurable RCS reduction

A gradient metasurface covered with water-based channels (GMWC) is proposed for RCS (radar cross section) reduction reconfiguration. The amplitude and phase response of the metasurface unit covered by the water-based channel (WC) is altered, which results in a change in the monostatic scattering of the GMWC. Under the normal incidence of X-polarized plane waves, the RCS reduction of GMWC shows different levels when different water channels are activated. The simulated results show that the average RCS reduction of GMWC increases from 5 dB to 20 dB in 5 dB steps in the 6 GHz to 8.2 GHz frequency band under four different reconstruction states (10000;01000;00100;00001). Besides, GMWC has an average RCS reduction of 10 dB within UWB (4–18 GHz) under state 10000. Finally, GMWC is fabricated and measured, and the measured results are in agreement with the simulated results. The RCS reduction reconfiguration characteristic of GMWC has potential application in target camouflage.