Radar Radome Research Articles

Development of an electromagnetic compatible composite-insert embedded in a double-curved sandwich panel

Composite sandwich structures, which are widely employed in engineering structures, require a multitude of inserts. In certain instances, the necessity for a specialized insert arises from the unique characteristics of a particular application. In applications such as weather radar radomes, double-curved sandwich panels should be designed with electromagnetic (EM) transparency as a primary objective. The use of metal inserts should be restricted to the absolute minimum. Given the limitations of using metal materials to protect against EM radiation and the need to enhance the load-bearing capacity of the joint against pull-out loads, a composite insert has developed as an innovative solution. In this study, a composite insert of a double-curved sandwich dome has been developed using silica nanoparticles, and its mechanical strength against pull-out load has been evaluated through both experimental and numerical analysis. The strength results obtained have been compared with analytical estimates. Additionally, the buckling of the double-curved sandwich dome against a wind speed of 220 km/h has been investigated numerically. The critical buckling load for wind loading for the full-scale sandwich radome was estimated to be 16,303 N. According to the numerical results obtained with the Abaqus finite element (FE) software, the maximum pull-out force applied to the connection area is approximately 10.7 kN. A parametric study of geometric variables and experimental results showed that it is possible to achieve a stronger composite insert (by 1 wt % nano silica particles) by 20.7% lighter and 102.65% more bearing capacity.

Reflection modulation generated by scale-free network resonator periodic structure

The pattern of resonator in a periodical array is decisive for its response under impinging electromagnetic wave. A scale-free network resonator is proposed by connecting sub-units in the form of scale free network. Scale-free network resonator array’s reflectivity near resonant frequency could be modulated at arbitrary value between zero and unity, which is different from known resonator array or frequency selective surface. Reflection amplitude modulation could generate rich behaviors, as effective medium property in wide band could be maintained near zero constant, which means zero phase shift and is favorable in radar radome structure. S-parameter analysis indicates amplitude modulation is owing to polarization conversion generated by network links. Scale-free network resonator array has application potentials in future radar radomes, electromagnetic wave lens and microwave antenna panels.

Trajectory Planning of Shape-Following Laser Cleaning Robot for the Aircraft Radar Radome Coating

Trajectory Planning of Shape-Following Laser Cleaning Robot for the Aircraft Radar Radome Coating

Nearly Ideal Transparency with Artificially Designed Meta-Atoms.

The ideal electromagnetic transparency refers to the ability of an object to remain scatteringless to any incoming waves, resulting in vacuum invisibility. However, natural solid substances can hardly be transparent in free space as they are responsive to external polarizations. Completely eliminating the polarization effect of an obstacle under arbitrary field illumination is a long-standing scientific challenge. Here, it is shown that a subwavelength meta-atom can be nearly ideally transparent in the vacuum. The overall vacuum-like property of the meta-atom is achieved through judiciously designing its internal polarization and magnetization. Remarkably, any large-scale objects made by stacking the meta-atoms inherit the vacuum-like property and are scatteringless in free space. By both the simulations and experiments, the meta-atom's peculiar property is reasonably verified. The proposed meta-atoms are excellent candidates for a wide range of applications, such as perfect radar radomes, scatteringless walls, filtering devices, and self-stealth materials.

A simple and efficient hydratable alumina gel‐casting method for the fabrication of high‐porosity mullite ceramics

AbstractIn this study, we have developed a method for the preparation of porous alumina‐containing ceramics by inorganic gel‐casting of hydratable alumina system. The gelation behavior of hydratable alumina in water and the high‐temperature phase evolution of alumina gels were clarified. In addition, extremely high‐porosity mullite ceramics were prepared using the hydratable alumina gel‐casting method combined with carbon fibers as the pore‐forming agent method. The as‐prepared mullite ceramics have a pore size of less than 10 μm, controllable high porosity of 90.6%–78.1%, a lightweight of 0.30–0.70 g cm−3, high compression strength of 1.41 ± 0.21–16.30 ± 0.20 MPa, low dielectric constants at 30 GHz of 1.34–1.79, the dielectric loss tangent of less than 3 × 10−3, and low thermal conductivities of 0.083–0.305 W/(m K). Lightweight, high strength, excellent dielectric properties, and outstanding thermal insulation indicate the potential of porous mullite ceramics for use in radar radomes or windows.

Numerical prediction of surface morphology and roughness in rotary ultrasonic face grinding SiO2f/SiO2 composite

The SiO2f/SiO2 ceramic matrix composite has been applied to fabricate high-performance radar radome because of its good wave transmission and mechanical property. The machined surface morphology and roughness of SiO2f/SiO2 ceramic matrix composite have an important impact on the service performance of radome products. This paper presented a numerical model to predict surface morphology for grinding of SiO2f/SiO2 composite. The prediction model was based on finite element method (FEM). Both conventional face grinding (CFG) and rotary ultrasonic face grinding (RUFG) of SiO2f/SiO2 composite were FEM simulated by integrating the microstructure of SiO2f/SiO2, the constitutive as well as failure mechanism of fiber/matrix, and the coupling grinding effect of multiple abrasive grits. The machined surface morphology was predicted by extracting node coordinates on simulated ground surface. The numerical prediction results were quantitatively validated using experimental results of ground surface roughness Sa. The application of the proposed prediction model not only elucidated the influence law of fiber orientations and machining parameters on ground surface quality but also revealed the different shear failure modes of SiO2 fiber during grinding process. The ground surface of SiO2f/SiO2 was deteriorated by uncut-off debonding fibers and fiber peeling pits. Ultrasonic-assisted vibration was beneficial to improve ground surface quality by force reduction and hammering effect caused by intermittent machining. However, the key prerequisite for the ultrasonic hammering effect to exert its process advantage was that the ultrasonic hammering energy could effectively fracture fibers on the ground surface rather than being absorbed by crack propagation at the fiber–matrix interface.

Wave-transparent electrothermal composite film for anti-icing/de-icing

Wave-transparent materials are essential to ensure the high-fidelity transmission of electromagnetic waves and to safeguard antenna systems in critical fields such as aerospace, transportation, and communication. However, surface icing of wave-transparent materials or antennas will severely impact their transmission and aerodynamic performance. In this study, a patterned electrothermal composite film (PEF) was prepared and optimized by relevant theories of electromagnetic leakage and frequency selective surface. The PEF demonstrated excellent rapid heating and stability, requiring only 0.4 W/cm2 power density to completely anti-ice in dynamic icing experiments. Additionally, the PEF boasted high transmittance, exceeding 80 % across an ultra-broadband range of 2–18 GHz. Furthermore, the PEF was lightweight and could be prepared in a large area. The results suggest that the PEF has the potential for valuable applications in radar radomes, wave-transmitting walls, and protective walls, particularly in cold areas.

Online prediction of grinding wheel condition and surface roughness for the fused silica ceramic composite material based on the monitored power signal

The fused silica ceramic matrix composite (SiO2f/SiO2) is characterized as one of the most promising materials in radar radomes and wave-transparent antenna windows. However, the ceramic matrix surface is rather rough, which reduces their service life in severe environments. Although precision grinding is used to improve surface quality, it gets difficult to precisely achieve the desired surface requirement due to the SiO2f/SiO2 material hardness, brittleness, and complicated fiber structure, as well as the uncertain wheel conditions. Especially the wheel condition and its influence on surface quality are unable to quantify directly. With the fast development of IoT monitoring and cyber-physical system, online prediction using process physics signals gains more interest. Power monitoring is a convenient way to obtain valuable grinding information at a relatively lower cost, making it more popular in the industry. However, the links between grinding parameters, power signal, and wheel conditions, surface quality is unclear. A series of grinding experiments of the SiO2f/SiO2 workpiece has been designed to demonstrate how the wheel conditions are indicated using the warm-cold density chart of specific grinding energy. A novel exponential polynomial model of surface roughness associated with wheel conditions indicated by the cutting power signal has been built. Compared with the conventional prediction model, REs center, MSE, and Pearson correlation coefficient are improved significantly from −0.0213, 0.029669, and 0.8695 to 0.0022, 0.022478, and 0.8710, respectively.

Dual-Band Omnidirectional Invisibility of a Thin Slab with Antiscattering Coatings on Both Sides

Making an object invisible means that an incident electromagnetic wave is not scattered with the object being present, which has been widely studied over the past few decades. Nevertheless, rendering omnidirectional invisibility for a large object in free space is still challenging. Here, we present a dual-band antiscattering coating using a double-layered metamaterial. By putting such coatings on both sides of a thin dielectric slab, omnidirectional invisibility is observed. It is shown that the peculiar double-layered metamaterial can provide electric polarization neutralization to the original thin slab, and the Maxwell Garnett mixing rule is safely invoked to guarantee the full elimination of scattering regardless of the incident angle. Full-wave simulations and experimental measurements exhibit that a composite made of a dielectric slab sandwiched by two antiscattering coatings can avoid any scattering in both the C and Ku bands with arbitrary incident angles. The proposed approach is quite simple and nondestructive to the original objects, which can be conveniently scaled to other scenarios including terahertz and optical applications, for boosting various internet of things devices, radar radomes, noninterference isolators in optics, and invisibility cloaks.

Optical meta-cage based on phase gradient metagrating

<sec>How to effectively control the refraction, reflection, propagation and wavefront of electromagnetic wave or light is always one of the advanced researches in the field of optics. In recent years, much effort has been devoted to both theoretical and experimental studies of optical phase gradient metagratings (PGMs) due to the fundamental interest and practical importance of PGMs, such as the generalized Snell’s law (GSL). Typically, the PGMs are constructed as periodic gratings consisting of a supercell spatially repeated along an interface, and each supercell consists of <i>m</i> unit cells, with <i>m</i> being an integer. The key idea of PGMs is to introduce an abrupt phase shift covering the range from 0 to <inline-formula><tex-math id="M2">\begin{document}$2\pi $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M2.png"/></alternatives></inline-formula> discretely through <i>m</i> unit cells to ensure the complete control of the outgoing waves. The phase gradient provides a new degree of freedom for the manipulation of light propagation, which has allowed a series of ultrathin devices to realize anomalous scattering, the photon spin Hall effect, and many other phenomena.</sec><sec>Intuitively, the number of unit cells <i>m</i> in a supercell does not influence the PGM diffraction characteristics, except that a small value of <i>m</i> will lead to a reduced diffraction efficiency. However, some recent studies have shown that the integer <i>m</i> plays a fundamental role in determining the high-order PGM diffractions when the incident angle is beyond the critical angle predicted by the GSL. In particular, for high-order PGM diffractions, <i>m</i> leads to a new set of diffraction equations expressed as</sec><sec> <inline-formula><tex-math id="M3">\begin{document}$ \left\{ {\begin{aligned} &{{k_x} = k_x^t - nG,{\text{ for odd L,}}} \\ &{{k_x} = k_x^r - nG,{\text{ for even L}}{\text{. }}} \end{aligned}} \right. $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20221696_M3.png"/></alternatives></inline-formula></sec><sec>In addition to the phase gradient, the integer number of unit cells <i>m</i> in a supercell is another degree of freedom that can be employed to control the light propagation. By the parity of <i>m</i>, the higher-order outgoing wave can be reversed between the anomalous transmission channel and the anomalous reflection channel.</sec><sec>In this work, according to the concept of abrupt phase and the parity-dependent diffraction law in phase gradient metagrating, we theoretically design and study an optical meta-cage. The meta-cage is a periodic structure with one period that contains <i>m</i> different unit cells. Through numerical simulations and rigorous analytical calculations, we find that the ability of meta-cage to trap light is related to the parity of the number of unit cells <i>m</i> in a supercell. Specifically, when the number of unit cells is odd, the point source placed in the meta-cage can perfectly radiate out of the meta-cage without any reflection. On the contrary, when the number of unit cells is even, the point source can hardly radiate out of the meta-cage, and all the energy is localized within the meta-cage. Moreover, such a phenomenon is robust against the disorder. These results can provide new ideas and theoretical guidance for designing new radar radome and photonic isolation devices.</sec>

A Miniaturized Frequency-Selective Rasorber With Absorption Bands on Two Sides of Passband for Antenna Dome

A miniaturized frequency-selective rasorber (FSR) with absorption bands on two sides of the passband is proposed in this letter. The FSR consists of one lossy frequency-selective surface (FSS) layer and one lossless FSS layer, and the equivalent circuit model of FSR is also analyzed. The lossy layer is composed of four electric-field-coupled (ELC) resonators loaded with four resistors, and the lossless layer comprises a square slot structure. By embedding the ELC resonators into the square ring, a passband can be added betweven the absorption bands, and the size of the overall structure can be reduced. Under normal incidence, the −10 dB absorption band is from 4.28 to 8.98 GHz and from 11.19 to 13.77 GHz. The transmission operates at 10 GHz and has a small insertion loss with 0.25 dB. Furthermore, an FSR prototype was fabricated and measured. The measured results are consistent with the simulation ones. The proposed FSR can be applied to radar radome to enhance the anti-interference and stealth performances.

Research on lightning impulse voltage discharge characteristics of electromagnetic metamaterials

Electromagnetic metamaterials have extraordinary electromagnetic characteristics., which make it widely used in the field of aircraft radar radome. However, they contain metallic microstructure units inside; which are easy to become the initial attachment area of lightning. In this paper, the combined gap lightning impulse test of the equivalent plate of electromagnetic metamaterial radome is carried out in experiment. High-speed camera was used to analysis the streamer development process. The interaction mechanism between lightning and metamaterial radome and the attachment characteristics of lightning to radome are analyzed experimentally. The research results are helpful to the lightning protection of electromagnetic metamaterial radome.

Effect of repeated thermal cycle on compressive properties of cyanate ester/quartz-based composites

The continuous fibre reinforced polymer composites are used in electronic circuits and radar radomes of defence aircraft due to lower transmission loss in the broadband microwave frequency region. Quartz fibre-reinforced cyanate ester composites are one of the best-suited materials for the radome structure of an aircraft offering exceptional electromagnetic transparency in varying operational temperatures. Moreover, this material possesses high-temperature capability with excellent mechanical and dielectric properties. The radome structure usually undergoes multiple thermal cycles during fabrication. In this work, to determine the compressive strength, a quartz/cyanate ester laminate was prepared with repeated thermal infusion followed by final curing (CE/Q_M) using resin film infusion (RFI) technique. The volume fraction of fibre, resin and void fraction were evaluated using the resin-burn off method. Finally, Ultrasonic C-scanning, a non-destructive quality evaluation and raster scanning using a multi-axis squirter system was carried out to detect and characterize the defects induced in the laminate. These data were compared to a sample produced with regular infusion followed by a curing cycle (CE/Q_S). The compressive strength of CE/Q_M (372.48 MPa) is measured to be 12% more than that of CE/Q_S (332.084 MPa). This is attributed to increased crosslink density in CE resin and strong interfacial adhesion between the resin and the fibre in the latter due to multiple thermal infusion cycles.

Diamond wheel grinding characteristics of 3D orthogonal quartz fiber reinforced silica ceramic matrix composite

Fiber-reinforced silica ceramic matrix composites (SiO2f/SiO2) have gained extensive attention in recent years for its applications in aeronautics field such as radar radome and window. However, the machining properties and mechanism of the material remain unclear. The features and mechanical properties of the material itself have a significant influence on both its machining characteristics and surface integrity. Thus, a full-factor grinding experiment is conducted using a 3D orthogonal SiO2f/SiO2 aiming to obtain its machining characteristics. The effects of grinding parameters and tools on the grinding force, surface roughness, and material damage type are investigated using a dynamometer, Scanning Electron Microscope (SEM), and Acoustic Emission (AE) analysis. The AE frequency band is analyzed, and a semi-analytical force model is established to study the difference between a single grain and wheel grinding. It was found that the changes in surface roughness correlate with the changes in grinding force, with fiber fracture being the main reason behind the increase in grinding force. Finally, the material removal mechanism was studied based on the AE analysis. It was found that the removal mechanism is fiber fracture dominated with matrix crack and debonding, and the primary sources of energy consumption are fiber fracture and friction.

Evaluation of electromagnetic effects on SINS with laser gyros, installed under radar's radome

Evaluation of electromagnetic effects on SINS with laser gyros, installed under radar's radome

A tunable metamaterial-based linear-to-circular polarization converter regulated solid state plasma in S-band

As the most widely used band in wireless communication systems, S-band is often used in many military and civil fields. In this paper, with the aid of the reconfigurability realized by the solid state plasma (SSP), a tunable metamaterial-based polarization converter is proposed and theoretically investigated. Through the premeditated excitation of the SSP resonators in the specific region, the linear-to-circular polarization conversions with two different operating states can be realized and switched to each other. The numerical results show that the polarization converter can obtain circularly polarized waves in two separate bands (2.15–2.63 GHz and 3.18–3.71 GHz) when our design is in State I, and the dual operating bands expands and merges into a consecutive ultra-wideband range (2.04–3.67 GHz) when our design is switched to State II. The total tunable working range of the presented polarization converter can essentially cover the whole S-band and the phenomenon of the isolation and fusion of the operating band possesses great potential application value in the fields of radar radomes, polarization separation, electromagnetic shielding, and so on.

Microstructure control and optimization of low temperature pressureless sintered silicon nitride−barium aluminosilicate composites

Silicon nitride–barium aluminosilicate (Si3N4/BAS) composites are promising materials for high temperature engineering applications. However, BAS is usually present in Si3N4 in the form of hexacelsian, which is an undesirable composition. In this work, the Si3N4/BAS composites containing both monoclinic-celsian and in-situ β-Si3N4 was prepared successfully. And the critical condition for coexistence of β-Si3N4 and monoclinic-celsian was also ascertained for the first time. Various methods were used to analyze the crystallization process of BAS in Si3N4 and the key factors affecting the crystallization process. Furthermore, all the prepared Si3N4/BAS composites have relatively high mechanical strength, low thermal expansion coefficient of 3.850 × 10−6/°C (32, 1000 °C) and good dielectric performance. It provides more implementation space for the structural control and optimization of Si3N4/BAS composites according to the application environment of material. This study will contribute to promote application of Si3N4/BAS composites in high temperature engineering fields such as radar radome and coating.

A Novel Instrument for Real-Time Measurement of Attenuation of Weather Radar Radome Including Its Outer Surface. Part I: The Concept

AbstractThis paper presents a unique instrument for characterizing the impact of wet radomes in radar systems. The proposed technique enables full radio frequency (RF) characterization of the radome, by evaluating its performance under a variety of conditions, including dirtiness, wetness, ice formation, and varying temperature, and providing a potential solution for future wet radome calibration methods. The reflections generated from the wet radome surface, measured from a high-resolution probe, are combined with an estimation of water absorption as a function of the precipitation rain rate, to calculate the attenuation introduced by the wet radome. This instrument is a cost-effective solution that can be integrated into an existing or new radar system.

A Novel Instrument for Real-Time Measurement of Attenuation of Weather Radar Radome Including Its Outer Surface. Part II: Applications

Abstract The concept and theory of a novel instrument to characterize the radio frequency performance of a radome under different conditions, including dirtiness, wetness, and varying temperature, was presented and discussed in Part I. The proposed concept estimates the transmittance through the radome using the reflected signal, directly measured, and an algorithm to evaluate the water absorption on the radome surface. In this second part of the paper, the proposed concept was employed to characterize the radome of an operative X-band weather radar in both dry and wet conditions.

Dynamic stability of rolling missiles with angle-of-attack feedback three-loop autopilot considering parasitic effect

This paper focuses on the dynamic stability of rolling missiles equipped with angle-of-attack feedback three-loop autopilot considering parasitic effect induced by radar radome slope. By analyzing the parasitic effect, it is found that an extra feedback loop occurs in the guidance and control system. This undesired loop will strongly affect the dynamic stability of rolling missile. Based on the differential equations expressed in the complex form, the sufficient and necessary stability condition for rolling missiles with angle-of-attack feedback three-loop autopilot considering parasitic effect is obtained. Numerical simulations and theoretical discussions are conducted to demonstrate the validity of stability condition. The results indicated that the rolling effect and parasitic effect will deteriorate the stability of autopilot designed in conventional method.