Radar Cross Section Reduction Research Articles

Dual Resonance Behavior and Enhanced Microwave Absorption Performance of Fe3O4@C@MoS2 Composites with Shape Magnetic Anisotropy.

Ternary hierarchical Fe3O4@C@MoS2 composites and binary hierarchical Fe3O4@C composites were successfully fabricated by a modified mixed solvothermal method, a self-oxidation polymerization method, and a hydrothermal process. Their magnetic properties and microwave absorption performance were investigated. Dual resonance behavior was observed in the Fe3O4@C@MoS2 composites. One of the resonances was attributed to natural resonance with a resonance frequency of 2.58 GHz, which was much higher than that for Fe3O4 bulk (1.5 GHz). The other originated from the superparamagnetic/ferromagnetic relaxation with a resonance frequency of 12.45 GHz. The minimum reflection loss (RLmin) reached -64.30 dB with a matched thickness of 2.24 mm at 11.64 GHz, and the maximum effective absorption bandwidth (EABmax) covered 6.39 GHz with a matched thickness of 1.89 mm. In addition, the maximum Radar cross section (RCS) reduction value reached 31.90 dB m2 at a scattering angle of 0°. Electron holography analysis confirmed a dense magnetic absorption network in the Fe3O4@C@MoS2 composites. The boost in microwave absorption performance was caused by the synergistic effects of magnetic and dielectric properties owing to the ternary hierarchical structure, shape magnetic anisotropy, and incorporation of 1T/2H MoS2. Besides, the binary hierarchical Fe3O4@C composites also exhibited good absorbing performance caused by natural resonance, with an RLmin of -52.90 dB at 5.80 mm, an EABmax of 5.98 GHz at 3.38 mm, and a relatively high RCS reduction value of 13.04 dB m2 at θ = 20°. This work paves the way for designing multicomponent hierarchical absorbers with broadband and intensive microwave absorption.

An ultra-wideband coding phase gradient metasurface for RCS reduction

ABSTRACTIn this work, an ultra-wideband coding phase gradient metasurface (CPGM) is proposed for radar cross section (RCS) reduction. The design process is presented in detail, in which eight types of coding elements are proposed firstly by using Pancharatnam-Berry (P-B) phase. The eight types of coding elements have different reflection direction or phase response under the same EM-wave incidence for they can introduce a series of phase gradients with different directions or starting-values under both right-handed and left-handed circular-polarized incidences, so the proposed CPGM composed of these coding elements has excellent performance in RCS reduction. The simulated results show that, compared with a pure metallic plate with the same size, the RCS of the CPGM can be reduced more than 10 dB in the ultra-wide frequency band of 9.2–46.2 GHz under normal incidence with arbitrary polarization, the relative bandwidth is up to 133.6%; moreover, the RCS reduction under oblique incidence with arbitrary polarization can still be kept larger than 9.3 dB in the frequency band of 13.1–42.5 GHz when the incident angle is increased to 45°. Finally, one experiment is carried out, a reasonable agreement exists between the simulated and experimental results.

A HYBRID STRUCTURE OF FREQUENCY SELECTIVE SURFACE AND MAGNETIC ABSORBING SALISBURY SCREEN FOR WIDEBAND RADAR CROSS SECTION REDUCTION

This article presents a novel hybrid physical mechanism that combines frequency selective surface (FSS) and Salisbury-type absorption to create a structure that can reduce the radar cross section (RCS) over a wide frequency range. The proposed design integrates a lossy sheet composed of a magnetic absorbing material (MAM) with a traditional Salisbury screen and a FSS of a T-ring resonator. The Salisbury screen effectively absorbs incoming waves when illuminated by a plane wave with normal incidence. Furthermore, the integration of a T-ring resonator generates high-order reflection beams, thereby enabling the selection of absorption band. Simulation results demonstrate that the proposed structure enables tunable RCS reduction between 2 and 18 GHz under various conditions with normal incidence. The combination of broadband absorption mechanism with frequency selective resonance allows to construct a perfect structure both in terms of bandwidth and frequency selection of absorption.

Facilitating learning adaptive V-tail of a supersonic missile for radar cross-section reduction during interval flight

To study the V-tail inclination of a supersonic missile that meet the requirements of low electromagnetic scattering characteristics in interval flight, an automatic tilt scheme is presented. The improved annealing algorithm is used to determine the optimal solution of the V-tail tilt angle, where multiple scattering of the physical optics plus physical theory of diffraction is used to calculate the radar cross section (RCS) of the target. The results show that the optimal solutions of V-tail inclination are different in various flight intervals of the horizontal observation field. In the forward side flight interval, changing the initial azimuth has less influence on the optimal solution of V-tail tilt angle, while more influence on the missile RCS indicator. In the side tail flight interval, the RCS level of the missile is low, and there is an optimal solution and a few feasible solutions for the V-tail inclination. The feasible solution of V-tail tilt angle in the lateral flight interval is obviously increased. The presented automatic tilt scheme is effective for studying the low scattering performance of the supersonic missile V-tail.

Investigations on electromagnetic scattering characteristics of aircraft rudder considering electromagnetic discontinuities

This work investigates the scattering characteristics of the rudder structure of aircraft considering electromagnetic discontinuities through multi level fast multipole algorithm (MLFMA) of the computational electromagnetics. Firstly, the scattering characteristics of the rudder seam and its influence on the omnidirectional radar cross section (RCS) are performed. Based on the traditional high-frequency analysis theory, the source and spatial contribution distribution of seam scattering are further studied. Numerical results demonstrate that the sidewall of the rudder seam is an important scattering source, and the radar absorbing material (RAM) coated on the sidewall of the seam has a good RCS reduction effect. In addition, this work presents the influence of the rudder deflection on the stealth performance, analyzes the effect of the rudder movement of the ordinary aileron and the split drag rudder on the scattering characteristics of the whole aircraft. The common aileron has little effect on the stealth performance of the aircraft, and it only causes scattering peak in the direction opposite to the control surface. However, the split drag rudder has great damage to the opposite direction stealth performance of the aircraft. When its deflection angle is 45°, the mean value of the opposite direction RCS increases by about two orders of magnitude compared with the deflection angle 0° state. The results indicate that the structure of aircraft rudder has a significant impact on the RCS characteristics of the whole aircraft.

RCS reduction metasurface based on orbital angular momentum

A novel radar cross-section (RCS) reduction metasurface is designed, fabricated, and experimentally characterized to flexibility control wavefront and efficiency generated orbital angular momentum (OAM). The metasurface is composed of several square loops with different reflection phases. Utilizing the property of the OAM phase singularity, the metasurface presents a significant RCS reduction along the propagation axis. Simulation results show that RCS reduction over 40 dB for normal incident plane waves at 7.6 GHz. For further clarity the physical mechanism of the RCS reduction, the near-field and 3D far-field features of the metasurface are discussed in detail. Two prototypes are fabricated and experimented with different topological charges. Good agreement is achieved between full-wave simulations and measurements. The design methodology provides an alternative to low-RCS and wavefront modulation design.

Broadband RCS reduction by means of disordered coding metasurfaces

Pattern Search (PS) optimization algorithm has been used for the design of disordered coding metasurfaces with the aim of reducing both monostatic and bistatic Radar Cross Section (RCS) in the 26–40 GHz frequency range. On this basis, high and low phase-state unit-cells have been defined with special attention to the minimization of coupling between the elementary patterns, thus allowing a quasi-constant 180° phase difference over a broad frequency range. Then, finite size metasurfaces have been designed and fabricated using the printed circuit board technological process. Finally, the experimental characterization of various disordered samples leads to −10 dB monostatic RCS reduction over a relative frequency band broader than 35% with a good agreement with both simulated and analytic theoretical predictions. This illustrates the relevance of disordered coded patterns for RCS reduction as well as the PS optimization approach as a design method of coding metasurfaces.

Extremely wideband low-RCS polarization conversion metasurface based on multivariate phase destructive interference.

In this paper, a polarization modulated metasurface to improve the magnitude and expand the bandwidth of radar cross section (RCS) reduction is presented. Two physical mechanisms are responsible for the reflection diffusion of the proposed metasurface. One is the functionality of controlling the spatial distribution of polarization response, and the other is the capability of spanning the entire 2π phase range by making full use of the variable sizes and height difference of unit cells to achieve superwideband phase cancellation. A 10 dB monostatic RCS reduction is obtained from 3.87 to 92.89 GHz (a ratio bandwidth of 24:1) for both polarizations under normal incidence by simulation, which is identical to experimental results and theoretical analysis. The proposed method for suppressing vector fields in an extremely wide band may hold promising potentials for suppression of acoustic, electromagnetic, optical and other elastic waves.

Wideband Multifunctional Polarization Converter: Application to Low Radar Cross-Section Radiating System

In this article, a wideband linear-to-linear and linear-to-circular reflective polarization converter is discussed. The proposed polarization converter can efficiently convert an incoming wave with a linear polarization into a reflected wave with orthogonal polarization in the frequency ranges: 7.63–12.21 GHz and 19.34–21.2 GHz. Moreover, a circularly polarized reflected wave in the frequency band of 13.85–18.50 GHz is also obtained. The proposed polarization converter constitutes a split-ring and a metallic strip cut in the middle designed on an ultrathin single substrate layer (thickness of 0.079λ o, where λ o corresponds to wavelength at center frequency of lowest operational bandwidth). The study related to angular dependence of the proposed polarization converter is also carried out and a stability upto 15° is achieved at the lower and upper-frequency bands of operation, respectively. A prototype of the proposed polarization with 25 × 25 cells of the converter is fabricated and measured. Measurement results are in consensus with their simulated counterparts. Furthermore, a 12 × 12 array of the proposed polarization converter is used to study the radar cross-section (RCS) reduction ability of a microstrip patch antenna operating in X-band. The average RCS reduction of about 11 dBsm is obtained at normal incidence. The proposed polarization converter can be utilized in X/Ku/K frequency band applications.

Low-profile shared-aperture metasurface array antenna with ultra-wideband radar cross section reduction and circularly polarization

This paper proposes a circularly-polarized (CP) metasurface antenna with ultra-wideband radar cross section (RCS) reduction. Initially, the relationship between RCS reduction and phase difference with different reflection amplitudes is analyzed theoretically. Inspired by the shared-aperture principle, a high-frequency resistive layer is introduced into the antenna element to further fulfill ultra-wideband RCS reduction and low-profile requirements. Numerical simulations demonstrate that the inserted layer has no effect on the radiation performance of the antenna array. Then, the proposed element and its orthogonal unit are arranged in a checkerboard pattern for good CP radiation. In this configuration, the proposed metasurface array antenna has a maximum gain of 16.7 dBi with 72.1% aperture efficiency. The bandwidth of 5 dB RCS reduction with x- and y-polarized incidences is 7.10–17.95 GHz and 7.34–17.85 GHz, respectively. The proposed design is verified by the fabrication of prototype antennas and measurements.

A wideband acoustic cloak based on radar cross section reduction and sound absorption

In this paper, by analogy with the theory of radar cross section (RCS) reduction in electromagnetics, we propose a design method for an acoustic invisibility cloak, which can achieve wideband acoustic stealth performance. The cloak consists of two sets of subwavelength metasurface units with phase differences within a range, which can achieve good RCS reduction in a wide band. At the same time, it overcomes the shortcomings of narrowband and high directional dependence of previous metasurface stealth cloaks based on phase gradient distribution. Using a simple resonant cavity metasurface structure, the invisibility cloak based on wideband scattering reduction and sound absorption is realized. Because of its simple structure and wide working frequency band, the RCS stealth cloak has wide engineering application potential.

A Low RCS and Array-Insensitive FSS Wideband Radome

In order to further expand the RCS reduction model of the miniature broadband antenna, a four-notch shaped FSS radome insensitive to the number of array elements is designed based on the multi-layered medium Green’s function and the transflective coefficient of the finite radome is derived. The calculated results are in good agreement with the infinite array, showing broadband transmission performance in both C-band and X-band. The electric field distribution and far-field distribution of a finite FSS array are given and the effects of a 5 × 5 array in a V-shaped structure on the surface of a miniature broadband antenna on its gain coefficient and RCS reduction characteristics are calculated numerically. The results show that the designed radome exhibits good array element insensitivity and far-field scattering reduction characteristics and achieves significant in-band and out-of-band RCS accurate reduction under the premise of constant antenna radiation performance. At normal incidence, the single-station RCS in the passband and stopband are as low as −35 dB and −32.66 dB, respectively. The maximum reduction in the transmission band reaches 20.96 dB under oblique incidence and the projection size of the radome decreases with the increase in the bottom angle of the radome but the RSC reduction performance is basically unaffected and can be adjusted flexibly according to actual needs. The above results provide a theoretical basis and technical support for the application of FSS radome in RCS reduction in micro wideband antennas.

In-situ construction of volcanic rock-like structures in Yb2O3 modified reduced graphene oxide and their boosted electromagnetic wave absorbing properties

Creating porous structures is a practical method for enhancing the impedance matching and interfacial polarization of dielectric materials, which in turn leads to improved electromagnetic (EM) wave absorption performance. However, the use of nanoparticles, nanorods, and two-dimensional materials to construct a simple porous structure typically has a minor effect on the EM parameters and interface polarization. To improve impedance matching and reduce the reflection of EM waves while simultaneously enhancing interfacial polarization, a more rational structure for dielectric materials is desired. Herein, a ytterbium oxide/reduced graphene oxide (Yb2O3/rGO) composite with a volcanic rock-like structure is proposed to exhibit outstanding impedance matching and loss capacity and achieve high EM wave performance. The addition of Yb2O3 is utilized to induce the formation of porous structures with varying morphologies. Yb2O3 not only significantly improves the polarization loss but also facilitates volcanic rock-like structure construction, thus improving the EM wave performance. As a result, the Yb2O3/rGO composites with a volcanic rock-like structure exhibit outstanding EM absorption performance, including three-band absorption (C, X, and Ku bands), as evidenced by their minimum reflection loss (RLmin) of −57.2 dB (equivalent to 99.9999% effective absorption) at 11.6 GHz when the matched thickness is 2.1 mm and an effective absorption bandwidth (EAB) of 4.2 GHz. Simulations in the CST microwave studio further validate the benefits of the composite's unique structure, which shows a radar cross-section (RCS) reduction value of up to 38.1 dB m2. This work offers valuable insights for the development of next-generation EM wave absorption materials through the implementation of a well-designed and distinctive structure.

Reconfigurable integrated structures with functions of Fabry–Perot antenna and wideband liquid absorber for radar system stealth

This paper proposes a functionally reconfigurable integrated structure of a Fabry–Perot (FP) antenna and wideband liquid absorber. First, a two-layer partial reflecting surface (PRS) has been designed. Then, a patch antenna is used to act as the source antenna. By combining the source antenna with the PRS, an FP antenna has been designed. What’s more, taking full advantage of the reflective properties of PRS, a liquid broadband absorber is then designed. Last, the integrated structure with two functions has been realized. It can be used as the FP antenna or the liquid absorber through the extraction and injection of ethanol. In this way, it is effective to switch between stealth and detection states which can be used in different electromagnetic environments. The PRS is elaborately tailored to serve as both a component of the FP antenna and the metal ground of the broadband liquid absorber. Then the integrated structure is realized by combining the FP antenna with the liquid absorber. The PRS is composed of patches on the top layer of the substrate and the square loop on the bottom. The liquid absorber is composed of a 3-D printed container, 45% ethanol layer and the PRS is used to serve as the metal ground. The formula of Mie resonance theory has been extended and used to design the liquid absorber. The gain of the antenna is 19.7 dBi when the ethanol is extracted. When the ethanol is injected, a wideband liquid absorber is achieved. The absorption band (S11 < − 10 dB) ranges from 4 to 18 GHz. The absorption bandwidth is over 133%. The monostatic RCS reduction bands of the structure with ethanol range from 4 to 18 GHz and the average RCS reduction is 28.4 dBsm. The measured and simulated results are in good agreement.

An Ultrathin Polarization Free Asterick-Shaped Metamaterial Absorber with Quad-Band Characteristics

In this paper, a quad-band absorber is proposed and developed, which is exhibiting ultrathin and polarization insensitive behaviour. It has been designed to be operated in S, C, and Ku bands with absorptions peaks at more than 95%. The proposed absorber is implemented on a FR4 glass epoxy laminate with an equivalent electrical thickness of 0.0108 λ0, where λ0 is the wavelength corresponding to the lowest frequency of operation. This confirms the ultrathin nature of the structure. The absorption performance of the proposed structure has been characterized under normal and oblique incidences followed by their experimental verification. Presented results demonstrate highly polarization-independent behavior of the proposed absorber due to its symmetric geometry. Also, the electromagnetic field distributions have been studied to acquire better insight of the absorption mechanism corresponding to distinct elements present in the structure. It is characterized in terms of its behavior as metamaterial, which ensures the miniaturization. The proposed absorber is suitable to be used in applications like radar cross section reduction, stealth technology, radio frequency identification, and electromagnetic compatibility.

Design and Implementation of a Novel Radar Cross Section Reduction Metasurface Covering 12.5-17.4 GHz and 20.5-36.2 GHz

Based on the theory of polarization conversion, this paper designs and implements two electromagnetic units with a 180-degree reflection phase difference in the range of 10-40 GHz. By coding and optimizing the spatial arrangement of the two basic units to obtain a metasurface, which makes the incident electromagnetic waves reflect diffusely, the energy in a single beam direction is reduced to realize the reduction of the radar cross section (RCS). The full wave simulated and experimental results of the reduction of the RCS of the metasurface have been presented. The RCS of the proposed metasurface can be reduced by more than 10 dB in the two broadband bands of 12.5-17.4 GHz and 20.5-36.2 GHz, and the maximum reduction can reach 26 dB, compared with a metallic surface of the same size. In addition, the optimized metasurface can also maintain a good reduction effect under oblique incident wave directions of 30, 45, 60, and 70 degrees. A very good agreement between simulation and measurement results is observed.

Wideband Low-RCS Step-Type Cavity-Backed Stacked Dielectric Resonator Antenna for Unmanned Aerial Vehicle Communications

This letter explains the design of a cavity-backed stacked dielectric resonator antenna (SDRA) with wider impedance bandwidth (IBW) and improved gain for C-band and S-band applications. The antenna mainly comprises of four dielectric resonators stacked above one another of varying size and shape. Combining the SDRA with step-type cavity and conformal radome forms the final antenna. The antenna provides a wider IBW of 103% (2.07–6.55 GHz), dual-band axial ratio bandwidth of 27.90% (2.38–3.15 GHz) and 16% (5.01–5.88 GHz), respectively. The antenna provides a maximum gain of 9 dBi. The final cavity-backed antenna offers a good radar cross-section reduction ranging from 2–8 GHz for both normal and oblique incidence angles. Hence the proposed SDRA with the dual-layer cavity is applicable for unmanned aerial vehicle communications.

A Super Diffuse Broadband RCS Reduction Surface Design Based on Rotated Phase Coding Polarization Conversion Metasurfaces

A Super Diffuse Broadband RCS Reduction Surface Design Based on Rotated Phase Coding Polarization Conversion Metasurfaces

Radar absorption characteristics of ceramic oxide fiber/aluminosilicate-sendust composite structure at ultrahigh temperatures

This study proposes a novel radar-absorption structure (RAS) composed of Nextel 601 fiber and a geopolymer-based aluminosilicate matrix for withstanding high temperatures and providing effective electromagnetic (EM) absorption performance. To measure its complex permittivity and permeability in the X-band frequency range, we dispersed flake-type sendust particles with different sizes and contents in the matrix. The complex permittivity increased with increasing size and content of the sendust particles, which was attributed to the increase in dielectric polarizations and electrical conductivity of the composites. Furthermore, the simulation studies of the designed RAS showed excellent EM absorption performance, with a thickness of 4.25 mm, revealed a maximum return loss (RLmax) of −24 dB with a broad absorption bandwidth (BW @ −10 dB) of 8.3 GHz at room temperature (RT). Similarly, the measurement of fabricated RAS exhibited a RLmax of −19.2 dB and a broad absorption BW of 5.45 GHz at RT in the S- and X-band frequency range (6.95–12.4 GHz). However, in X-band measurements conducted at elevated temperatures, the RLmax values declined, reaching −8.04 dB at 9.87 GHz and −10.97 dB at 9.45 GHz observed at 900 °C and 1200 °C, respectively. This decrease in EM absorption performance can be ascribed to variations in impedance matching conditions arising from factors such as dielectric and magnetic losses, as well as shifts in frequency. In addition, the significant RCS reduction of the proposed RAS indicates its applicability to hypersonic aircraft.

Ultra-Thin Fss Based Radar Absorbing Structure For X-Band Applications

Radar Absorbing Structures (RAS) are widely used in defense applications in order to reduce the electromagnetic reflections from predominant hotspots. With majority of military radars operating in X-band, thin frequency selective absorbers catering to this frequency range are the need of the hour especially for airborne platforms. In this regard, a novel ultra-thin Frequency Selective Surface (FSS) based RAS with superior absorption performance in the frequency range of 8GHz to 12GHz is presented. The absorption characteristics and radar cross-section (RCS) of the RAS has been analysed using commercially available EM simulation software. Further, the ultra-thin RAS, with a thickness of 0.053l at the centre frequency, has been fabricated and the performance parameters have been measured. The measurement results show that the percentage of power absorbed by the proposed RAS is greater than 90% over majority of X-band. In addition, it provides atleast 8dB RCS reduction (RCSR) in monostatic as well as bistatic modes of operation in comparison with its metallic counterpart of identical dimensions.