Radar Absorbing Research Articles

Control of dielectric properties of micropattern printed fabric for radar absorbing structures

Recently, research has been carried out on radar absorbing structures (RASs) that simultaneously perform structural functions and provide low observability. The method of imparting conductivity by mixing a resin with conductive particles, such as carbon nanotubes, has been utilized since the early stages of RASs. This is advantageous because it enables high permittivity through a relatively simple process. However, the electromagnetic properties vary considerably, and the structure fabrication is complicated owing to the high viscosity. Additionally, it is challenging to analytically predict the electromagnetic properties of specimens before their permittivity can be measured. In this study, a high permittivity composite material was investigated, wherein the permittivity can be controlled and predicted analytically. Printed electronics were applied on the surface of glass fabric using a conductive paste to produce a micropattern printed fabric (MPF). The MPF was then studied to predict and control the permittivity of the composite material. In an MPF, conductive particles are distributed into micropatterns designed on the surface of glass fabric; therefore, uniform permittivity was obtained and could be controlled by moderating the parameters of micropatterns, such as pattern size and aspect ratio. The mechanical properties of the MPF were also investigated.

VMFNet: visual-microwave dual-modality real-time target detection model for detecting damage to curved radar absorbing materials.

Damage to radar absorbing materials (RAMs) reduces the stealth capabilities and battlefield survivability of the equipment. Research on RAM damage detection technology is key to outfield equipment maintenance. In this paper, an intelligent RAM damage detection method based on visual and microwave modalities is proposed. A compressed sensing planar-scanning microwave imaging method based on a range migration algorithm (RMA) imaging operator and fast Gaussian gridding nonuniform fast Fourier transform (FGG-NUFFT) is proposed, achieving high imaging quality and speed. A dual-modality, curved RAM dataset (DCR dataset) is constructed, composed of visual images and microwave images showing two kinds of damage: round shedding and strip cracks. A new dual-modality target detection model, the visual-microwave fusion network (VMFNet), is designed to detect RAM damage. Its mean average precision (mAP) reaches 81.87%, and its inference speed reaches 35.91 fps. A visual network (VisNet) and microwave network (MicNet) are designed as the backbone of VMFNet for extracting the visual and microwave features of RAMs. A path aggregation network (PANet) unit is designed to fuse the multiscale features of the two modalities, resulting in good retention of shallow-level features and high detection accuracy. The head contains different receptive fields and outputs three scales of detection results, effectively detecting damage of different sizes.

Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe1.9Gd0.1O4) nanoparticles and CoFe1.9Gd0.1O4/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe1.9Gd0.1O4 nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe1.9Gd0.1O4 ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe1.9Gd0.1O4 ferrite nanoparticles and CoFe1.9Gd0.1O4/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe1.9Gd0.1O4/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.

Preparation, Characterization, and Microwave Absorption Properties of Cobalt-Doped SrFe12O19 Nanoparticles

Ferrite is the major absorbing components of conventional radar absorbing materials (RAM). However, conventional RAM made of the single-absorbing components cannot meet the comprehensive requirements of “thin, wide, light, and strong.” To overcome this limitation, a composite compound of cobalt-doped SrFe12O19 nanoparticles is currently exploited to improve absorbing ability. SrFe12−xCoxO19 (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25) composite ferrites were prepared using the sol-gel method. Results show that the powders obtained are pure lead-magnetite ferrite, and the properties of the samples are improved evidently after Co substitution. At room temperature, the samples substituted using Co exhibit typical permanent magnetism. When x = 0.2, the maximum saturation magnetization and coercivity of the powders are 55.8 A·2/kg and 302.4 kA/m, respectively. The real complex permittivity part of SrFe12−xCoxO19 first increases and then decreases with the increase in x and has a maximum value of x = 0.2. The complex imaginary permittivity part fluctuates with the increase in x; it first decreases, then increases, and finally decreases. With the increase in x, the complex permeability real part of the sample does not change much between 2 GHz to 16 GHz but first increases and then decreases in the range of 16-18 GHz. The imaginary part of the complex permeability first increases and then decreases, reaching its maximum at x = 0.2. The attenuation constants and absorbing properties of the samples before and after substitution were analyzed. The matching thickness of strontium ferrite (SrFe12O19) is 5.2 mm, the matching thickness of SrFe11,8Co0.2O19 (x = 0.2) is reduced to 2.4 mm, the minimum reflectivity is −24.7 dB (13.8 GHz), and the microwave absorption bandwidth lower than −10 dB is 4.7 GHz (11.6-16.3 GHz). These results indicate that an appropriate amount of Co substitution could greatly improve the absorbing performance of SrFe12O19. This study provides a simple method for the preparation of Co doped strontium ferrite. The microwave absorbing properties of the composite powders are excellent and have potential engineering application value.

Thickness optimization of a double-layered microwave absorber combining magnetic and dielectric particles

The purpose of this study is to optimize the thickness of the double-layered microwave absorber for obtaining the highest absorption. The graphenic-based carbon compounds and Fe3O4 magnetic particles were combined to fabricate the double-layered absorber. The thickness was optimized by employing a genetic algorithm (GA) to obtain high reflection loss values. These samples at a thickness of 2 mm were measured for reflection loss (RL) with a Vector Network Analyzer (VNA). Input variables, such as relatively complex permeability and relatively complex permittivity, were obtained using a conversion program that uses Nicolson-Ross-Weir (NRW) method from VNA S-parameter values (S11 and S21) data. By entering the permeability and permittivity of the complex relative to GA, the thickness can be optimized to produce high value. Optimization of the double-layer thickness of 12 absorbers produces the optimum thickness of = 5.99 mm and = 0.87 mm among the materials combination, which results in a high (−44.69 dB). This optimization is very important for designing double-layer radar absorbing material (RAM) which results in high values.

Impact of the exfoliated graphite on magnetic and microwave properties of the hexaferrite-based composites

RAM (Radar absorbing materials) is strategically important to prevent the targets from being identified. A necessary condition for the absorption of most of the incoming radiation, depending on a combination of conductivity, permittivity, and permeability of the composite's different components, is wave impedances balanced at an air/shield interface. The paper presents a novel RAM developed with the use of exfoliated graphite (EG) for the preparation of composite samples in polyvinyl fluoride (PVDF) in the presence of magnetic inclusion of hexaferrite (HF). The prepared samples were characterized by X-ray diffraction (XRD) and Raman spectroscopy. The morphology was studied by using scanning electron microscopy (SEM). The magnetic properties of all the samples were analyzed by using a vibrating sample magnetometer (VSM). The composites were tested for RAM properties using a vector network analyzer (VNA) in the range of 0.7–7 GHz. The study shows the optimum weight percentage of HF, PVDF, and EG for obtaining high RAM. Inside the prepared composites, EG acts as a conductive path, increasing dielectric and magnetic losses, both of which are critical for trapping incoming electromagnetic radiations and improving total electromagnetic shielding by absorption. In maintaining conductive trajectories in electromagnetic radiation absorption, EG has a significant role in raising the overall shielding efficiency (performance) by more than 50 dB, indicating that the prepared composites in this study can absorb 99.9% of the incoming electromagnetic radiation. The studied composites can be promising absorption blocks in electromagnetic interference (EMI) shielding applications.

Intrinsically conducting polymer (ICP) coated aramid fiber reinforced composites for broadband radar absorbing structures (RAS)

In this study, a composite radar absorbing structure (RAS) was developed using intrinsically conducting polymer (ICP)-coated aramid fiber reinforced polymer composites (AFRPs). Dielectric aramid fibers fabric were fabricated by simple dip-coating with PEDOT:PSS and PANI:CSA conducting polymers. The electrical conductivity, dielectric constant, radar absorbing performance in the X-band range (8–12 GHz) and mechanical properties of the ICP-coated AFRP RAS were investigated with respect to the type and composition ratio. As a result, the optimal type and composition ratio of the ICPs were presented. The facile process of the ICP coating on the reinforcing fibers will help further the exploitation of conducting polymers for RAS.

Fabrication and assessment of an electrochromic and radar-absorbent dual device based on the new smart polythiophene-based/RGO/Fe3O4 ternary nanocomposite

Both polymeric electrochromic and radar absorption materials have been considered as science hotspots over the past few decades. However, integrating both properties (electrochromic and radar absorption) in a single device has not been addressed to fabricate a multifunctional device so far. Thus, here, we endeavor to shed light on this uncharted area by presenting a new smart ternary nanocomposite (polythiophene-based/RGO-Fe3O4) which can provide both electrochromic and microwave absorbent features simultaneously. In this regard, we synthesized the binary Fe3O4-RGO nanocomposites with different contents of Fe3O4 nanoparticles. Then, this binary nanocomposite is utilized in combination with a polythiophene-based conductive polymer as a tricolor (RGB) organic electrochromic material to synthesize the smart ternary nanocomposite through both in-situ polymerization and physical mixing methods. The ternary nanocomposites containing different weight fractions of Fe3O4-RGO nanoparticles were used to assemble the rigid and flexible ECD devices using flat and fiber substrates such as glass-indium tin oxide (glass-ITO), polyethylene terephthalate-indium tin oxide (PET-ITO) and stainless steel wire (SSW). By applying a voltage of −2.1 to 2.1 v, a reversible color-switching ability was observed between green color (oxidized state), and red color (reduced state) for all ECDs. The average switching time and color memory for the SSW cell were determined to be about 3 s and 155 min, and for both glass-ITO and PET-ITO cells to be 2 s and 210 min, respectively. Additionally, the microwave absorption properties of the prepared ternary nanocomposites were characterized by measuring the electromagnetic parameters such as permittivity, permeability, and reflection loss. A ternary nanocomposite with 3 mm thickness filled with 50 wt% Fe3O4-RGO exhibited a maximum reflection loss as high as −30.2 dB (92% absorption) at 12.3 GHz (in the range of x-bond) with 1.1 GHz bandwidth.

Effect of Filler Concentration and Time Sonication of ZnO Composite for Radar Absorbing Material Applications

Effects of filler concentration and sonication time on the structure, morphology, reflection loss and absorption percentage of ZnO composite was investigated. The structure, morphology, reflection loss and absorption percentage of the composite was investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Vector Network Analyzer (VNA). The ZnO composite was made by solution mixing method with the epoxy resin as a filler varied of 10 wt%, 20 wt%, and 30 wt%. The hardener was mixed to the ZnO composite by the composition of 2: 1. The sonication time was varied of 30, 45 and 60 minutes. The XRD showed that the crystal structure of ZnO composite was confirmed as a hexagonal structure and the structure was not change for all composite. The VNA results showed that the optimum reflection loss value was-9.37042 dB at the frequency of 12.3 GHz for the filler composition of 20 wt% and sonification time of 45 minutes. On the other hand, the minimum reflection loss value was-6.86845 dB at the frequency of 12.3 GHz for the filler composition of 10 wt% and sonification time of 45 minutes. In addition, the optimum absorption percentage was 18 % at a filler composition of 10 wt% with 60 minutes sonication time. This study demonstrates a promising method to improve a microwave absorption of ZnO composites.

Wide-angle, Ultra-wideband, and Polarization-insensitive Circuit Analog Absorbers

Most previous circuit analog absorbers only considered absorption performance under normal incidences, leading to bad absorption for large incident angles, particularly those > 30°. With the advancement in modern bistatic radar detection technology, radar electromagnetic waves may come from different spatial directions, thereby necessitating radar absorbers with high absorption performance under normal and oblique incidences. Thus, in this paper, we present a novel wideband absorber comprising a conductive square-loop array embedded with lumped resistors and a well-designed Wide-Angle Impedance Matching (WAIM) layer. Results show that the WAIM layer can significantly improve absorption under oblique incidences. To make the absorber design clear and simple, an Equivalent Circuit (EC) and strict calculating formulas are proposed under normal and oblique incidences. Fractional bandwidth is increased into 137.1% through measurement under normal incidence, and the structure has a common fractional bandwidth of at least 110.5% for at least 10 dB reflection reduction when the incidence angle < 45°. The similarity among EC calculated, simulated, and measured results proves the validity of the designed absorber.

Design of an Optical Transparent Absorber and Defect Diagnostics Analysis Based on Near-Field Measurement.

To reduce the electromagnetic wave interference caused by cavity resonance or electromagnetic wave leakage, herein, an optical transparent radar absorbing structure (RAS) was designed using transparent conductive oxides (TCOs) with a high optical transmittance and electrical conductivity, and a procedure was proposed for detecting possible defects in the fabrication and operation and for assessing the influence of the defects on the electromagnetic performance. To detect locally occurring defects in planar and three-dimensional absorbing structures, a measurement system based on an open-ended near-field antenna capable of producing small beam spots at a close distance was constructed. Moreover, the reflection characteristics of the transparent RAS were derived from a simplified multiple reflection equation, and the derived results were compared with the analysis results of an equivalent circuit model to predict the surface resistance of the TCO coating layer, based on which the presence of defects could be confirmed. By using the experimental results, the predicted surface resistance results of the coating layer and the results measured using a non-contact sheet resistance meter were compared and were found to correspond, thereby confirming the effectiveness of the proposed defect detection method.

Additively manufactured metastructure design for broadband radar absorption

BackgroundRecent advances in material science and electronics led to the rapid development of communication devices and radar detection techniques resulting in an ever-increasing demand for improved stealth performance of air vehicles during scouts. Absorber design employing metastructure concept has recently become a popular approach to improving radar stealth performance. Metastructure permits the realization of desired absorption characteristics by careful design of geometrical structures and material compositions. In this study, a metastructure designed based on graphite SLS composite for radar absorption has been demonstrated. The unit cell of the proposed structure is simulated by COMSOL Multiphysics to determine the frequency-dependent absorption characteristic of the structure. It is fabricated by using a low-cost selective laser sintering technique of additive manufacturing technology.ResultsThe prototype, while measured, shows effective absorption bandwidth of 1.04 GHz that is in reasonable agreement with the simulated response of 2.08 GHz. The optimized structure exhibits ≤ − 10 dB reflectivity within a broad frequency range extending from 7.60 GHz to 18.00 GHz under normal incidence in both TE and TM polarizations. Furthermore, the absorption performance under different polarizations and incident angles has been investigated. Results indicate that the absorber displays polarization indifference and exhibits a wide-angle of incidence tolerance of up to 45° in TE polarization and 30° in TM polarizations.ConclusionIn this paper, the feasibility of using graphite SLS material to design and 3D print a metastructure design for radar absorbing has been established as confirmed by the simulation and the measurement results. The advantages of low cost, ultra-broad operating band, wide-angle of incidence feature, and polarization insensitivity qualifies the proposed absorber for stealth and electromagnetic shielding applications.

Development and Investigation of PEDOT:PSS Composition Coated Fabrics Intended for Microwave Shielding and Absorption.

This study presents the investigation of the electromagnetic properties and resistance performance of electrically conductive fabrics coated with composition containing the conjugated polymer system poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS). The developed fabrics were intended for electromagnetic radiation (EMR) shielding in microwave range and for absorbing microwaves in radar operating range, so as to act as radar absorbing materials (RAM). The measurements of reflection and transmission of the developed fabrics were performed in a frequency range of 2–18 GHz, which covers the defined frequencies relevant to the application. Four types of fabrics with different fiber composition (polyamide; polyamide/cotton; wool and para-aramid/viscose) were selected and coated with conductive paste using screen printing method. It was found that EMR shielding effectiveness (SE) as well as absorption properties depend not only the amount of conductive paste topped on the fabric, but also resides in the construction parameters of fabrics. Depending on such fabric structural parameters as density, mass per unit area, type of weave, a layer of shield (or coating) just sticks on the fabric surface or penetrates into fabric, changing the shield thickness and herewith turning SE results. Meanwhile, the fiber composition of fabrics influences mostly bonding between fibers and polymer coating. To improve the resistance performance of the developed samples, a conventional textile surface modification technique, atmospheric plasma treatment, was applied. Initially, before plasma treatment and after treatment the fabrics were evaluated regarding an aqueous liquid repellency test, measuring the contact angles for the water solvent. The influence of plasma treatment on resistance performance of coated fabrics was evaluated by subjecting the plasma treated samples and untreated samples to abrasion in the Martindale abrasion apparatus and to multiplex washing cycles. These investigations revealed that applied plasma treatment visibly improved abrasion resistance as a result of better adhesion of the coating. However, washing resistance increased not so considerably.

High temperature metamaterial enhanced electromagnetic absorbing coating prepared with alumina ceramic

At present, a series of challenges are impeding large-scale application of high temperature radar absorbing coatings (RACs), such as complex preparation of raw material and complicated technology of processing. In this paper, we designed and experimentally demonstrated a high-temperature metamaterial RAC (MRAC) with strong absorption and thin thickness, which is composite of radar absorbing coating and a layer of metamaterial. To avoid complex preparation of raw materials, pure alumina was selected as the radar absorbing coating. Plasma spraying and screen printing were employed to simplify the sample preparation to produce the absorbing coating and the metamaterial layer, ensuring its feasibility and practicality. The metamaterial layer was prepared with a high temperature conductive paste and it improved the impedance matching of the coating and regulated the electromagnetic (EM) resonance, which allows more EM waves to be absorbed. Therefore, excellent high temperature absorption was also achieved with relatively small thickness. At 800 °C, the MRAC reflection loss (RL) below −5 dB almost covered the frequency of 10–18 GHz with a thickness of only 1.5 mm. This new metamaterial has broad application prospects by the virtue of its simplicity and convenience in manufacture.

Simple synthesis of conductive poly aniline/cobalt ferrite magnetic nanocomposite: its radio waves absorption and photo catalyst ability

Photo-catalytic activity of cobalt ferrite/polyaniline magnetic nanocomposite was investigated for degradation of four Azo dyes (acid black, acid brown, acid violet and Congo red). For this purpose at the first step CoFe2O4 nanoparticles was synthesized via a fast and simple precipitation method. CoFe2O4/polyaniline nanocomposites were then prepared using simple polymerization method of aniline monomer. The absorption property of radio waves in the microwaves band by cobalt ferrite–polyaniline nanocomposites was studied as well. The results introduce the cobalt ferrite–polyaniline nanocomposites as a radar absorbing coatings. The crystal structure was studied using X-ray diffraction and particle size was determined by scanning electron microscopy. Vibrating sample magnetometer was used for magnetic analysis and by applying Fourier transform infrared spectrometer, the purity of the material was also determined. Photocatalytic activity of nanocomposites was investigated by analyzing UV–Vis spectrograph. In order to examine the radar absorption properties of cobalt ferrite/polyaniline nanocomposites, the absorption of radio waves in the range of 8–12 GHz was measured. These samples have absorption peaks around bandwidth 12–12.5 GHz and absorption amounts were about 70 percent and decrease reflecting was around − 6.4 dB frequency ranges.

Radar Absorbing NiCo Nanoparticles in Carbon Matrix of Nanocomposites in the Microwave Range

The paper focuses on the synthesis of NiCo/C nanocomposites comprising the Ni–Co alloy nanoparticles uniformly distributed and stabilized in a carbon matrix. The synthesis is performed by using IR pyrolysis of organometallic precursors obtained from a mixture of dymethylformamide solutions of polyacrylonitrile, nickel and cobalt chloride hexahydrates. It is shown how the synthesis temperature and the metal concentration in precursors affect the size and composition of the Ni–Co alloy nanoparticles. Electromagnetic properties of NiCo/C nanocomposites are investigated in the range of 3–12 GHz. The influence of the synthesis conditions is studied in relation to the frequency profiles of the reflection and absorption coefficients. It is shown that radar absorbing properties of NiCo/C nanocomposites can be controlled by changing the synthesis conditions.

Enhancing Microwave Absorbing Properties of Nickel-Zinc-Ferrite with Multi-walled Carbon Nanotubes (MWCNT) Loading at Higher Gigahertz Frequency

The rapid growth of electronic systems and devices operating within the gigahertz (GHz) frequency range has increased electromagnetic interference. In order to eliminate or reduce the spurious electromagnetic radiation levels more closely in different applications, there is strong research interest in electromagnetic absorber technology. Moreover, there is still a lack of ability to absorb electromagnetic radiation in a broad frequency range using thin thickness. Thus, this study examined the effect of incorporating magnetic and dielectric materials into the polymer matrix for the processing of radar absorbing materials. The experiment evaluated the sample preparation with different weight percentages of multi-walled carbon nanotubes (MWCNT) mixed with Ni0.5Zn0.5Fe2O4 (Nickel-Zinc-Ferrite) loaded into epoxy (P) as a matrix. The prepared samples were analysed by examining the reflectivity measurements in the 8 – 18 GHz frequency range and conducting a morphological study using scanning electron microscopy analyses. The correlation of the results showed that different amounts of MWCNT influenced the performance of the microwave absorber. As the amount of MWCNTs increased, the reflection loss (RL) peak shifted towards a lower frequency range and the trend was similar for all thicknesses. The highest RL was achieved when the content of MWCNTs was 2 wt% with a thickness of 2 mm with an RL of – 14 dB at 16 GHz. The 2.5 GHz bandwidth corresponded to the RL below -10 dB (90% absorption) in the range of 14.5 – 17 GHz. This study showed that the proposed experimental route provided flexible absorbers with suitable absorption values by mixing only 2 wt% of MWCNTs.

Phase Transition of Fe₃O₄ Magnetic Material Based on Observation of Curie Temperature and Hysteresis Curve: Micromagnetic Simulation Study

Phase transition yesng happens to the material magnetite (Fe3O4) is an interesting phenomenon to study because it has many important applications, one of which is RAM (Radar Absorbing Material). The magnetic properties of nanomaterials are known to be influenced by their size. In this simulation research, the research objective was to analyze the temperature value of the Curie and the hysteresis curve of the Fe3O4 material with variations in the size of the material sample cube of 5 nm, 8 nm, 10 nm, 12 nm, and 15 nm. In this study, using a micromagnetic simulation method based on atomistic models with the Vampire program. The results showed that the Curie temperature value in the Fe3O4 material was influenced by variations in the size of the material. The Curie temperature values when the side sizes of the cube are 5 nm, 8 nm, 10 nm, 12 nm, and 15 nm, namely 650 K, 635 K, 650 K, 665 K and 645 K. The characteristics of the hysteresis curve for Fe3O4 material based on simulations at each material size (5 nm, 8 nm, 10 nm, 12 nm, and 15 nm) for several temperatures (0 K, 328 K, 473 K and 773 K) indicate that there is a change in the coercivity and field values. saturation.

Microwave Heat-Treated Electronic Waste Constituted X-Band Radar Absorbing Structure Using Electromagnetic Mixing Model Assisted Optimization Strategy

Potential radar absorbing material (RAM) for suppressing electromagnetic (EM) wave over a range of oblique angles of incidence are needed in many applications. In this article, an attempt is being made to build cost-effective and efficient RAM using the EM characterization of microwave heat-treated (MHT) electronic waste followed by an EM mixing model-assisted analytical approach. The robust and facile top-down fabrication technique is employed for the development of heterogeneous composites, which are further subjected to microwave heat treatment at distinct power wattages. The magneto-dielectric spectrographic analysis of samples is carried out in the range of 8.2 to 12.4 GHz. The Debye parameters are optimized and succeeded to obey EM property of the synthesized samples. Jaya's algorithm is adopted for the optimal design of single and dual-layer RAMs at normal and oblique angle incidence based on the constitutive EM parameters under certain restrictive conditions. The embraced MHT method prompts an improvement in microstructure coherency that further increases absorption bandwidth (BW). As a result, a 2.1 mm thick single layer RAM achieves a minimum reflection coefficient (RC) of -17.1 dB at 10.3 GHz with a 100% BW below -10 dB threshold. The groundbreaking findings are obtained by performing a three-fold study of dual-layer RAMs, culminating a minimum RC of -47.8 dB at 11.8 GHz with a layer thickness of 1.8 mm. This article shows that the microwave heat-treated composites have enormous potential in the development of lightweight and broadband RAMs for stealth applications.

In‐band radar cross‐section reduction of the slot array antennas by RAM‐based frequency selective surfaces

A method for reducing radar cross-section (RCS) of the slot array antenna by utilising the radar absorbing material, while preserving the radiation performance simultaneously, is proposed and discussed. The scheme is based on the implementation of the multilayer frequency selective surface-radar-absorbing material (RAM) capable of operation over a wide frequency band. The use of radar absorbing material on an antenna’s radiation screen causes a change in surface current, resulting in the radiation pattern of the antenna. Therefore, by designing the coating pattern of the radar absorbent material as a substrate and a capacitive patch as a unit cell on the antenna board, the reduction of 19 dB RCS at X-band and minimum antenna gain loss (3dB) is achieved. To demonstrate the proposed solution, a 30-cm diameter slot array antenna, which is considered as a test case, is coated by RAM and radar cross section reduction (RCSR) is dramatically accomplished over a frequency band ranging from 8 to 12 GHz. It is worth mentioning that the obtained RCSR at 9.4 GHz is as much as 19 dB. Subsequently, the proposed method can be a candidate for reduction of RCS in slot array antennas, considering the remarkable RCSR and acceptable effect on radiation characteristics.