Papers by Keyword: Radome

Abstract: The porous silicon nitride ceramics with low dielectric constant and high flexural strength were obtained by adding pore-forming agent through partial sintering technique. The effects of pore-forming agent amount on the properties of porous silicon nitride ceramics were investigated. Microstructure was analyzed by means of scanning electron microscopy. The results show that the porous structure is formed by the overlap of pillar β-Si₃N₄ with high length diameter ratio. The porosity of samples rises with the increase of pore-forming agent content, which leads to the decrease of the dielectric constant and loss, but the decrease of flexural strength. When the pore-forming agent of PMMA with mass fraction of 20% was added, the volume density, porosity, dielectric constant and loss of porous silicon nitride ceramics were 1.17g/cm³, 66.5%, 2.33 and 0.8×10^-3 respectively, with higher flexural strength of 75MPa which is satisfactory as low dielectric material for core layer of broadband radome.

Abstract: In this paper, both the permittivity and the microwave transmittance properties of organosilicon-matrix composites under different temperatures have been studied. In order to investigate the reason for the changing of dielectric property, both TGA and high-temperature dielectric spectrum measurement have been carried out. A theoretical model of radome, with a temperature gradient distribution, has been built to analyze the dependence of microwave transmittance property on temperature. Based on the experimental results, we can optimize the effective operating temperature of this kind of organosilicone-matrix composites.

Abstract: With the process optimizing, electromagnetic performance designing, structural strength/stiffness checking and testing, a cost-effective and environment-friendly approach to manufacturing a submarine radome and its related products at low cost is introduced in this article: The submarine radome is made of an epoxy-matrix composite reinforced with E-glass fabric through the vacuum infusion and heating cure processing.

Abstract:

This paper investigates the quasi static compression analysis behavior of a biocomposite radome using nonlinear static modeling. Bio-based fiber is proposed to be used in aircraft radome due to its low dielectric constant. In this instance, kenaf was being utilized as the natural fiber to form a hybrid combination of fiberglass/kenaf epoxy laminates. The quasi static behavior was modeled using MDNastran SOL106 Nonlinear Static. The radome was modeled as a hemispherical shell based on Beechcraft’s radome geometric configuration. The radome is designed as a four-layered laminates with randomly oriented fiberglass and kenaf. The nonlinear compression was performed in the range of 0.01 mm to 0.49 mm with a maximum reaction force of 189 N. The radome was not displaced equally or symmetrically as the translational load applied since the shape of radome is asymmetry and the surface at the top is uneven. The increment of the forces leads to elastic local flattening deformation at the apex of the radome. Its shape influences in determining the displacement and the stress to the radome.

Abstract: In this paper, we describes a novel periodical electromagnetic structure. This hybrid structure consists of an absorber layer and a frequency selective surface (FSS) layer, so-called AbFSS structure. These two layers share one dielectric substrate. The absorber layer works at K band and the FSS layer performs at X band. The unit of this structure is numerically studied. A design procedure is developed after this study. Then an AbFSS antenna radome is modelled and applied to a 2x2 microstrip patch array. The characteristics of the array with and without this novel radome are researched. The characteristics include antenna gain and monostatic RCS. The comparisons of these characteristics of the array with and without the radome demonstrate that this radome is transparent at X band and absorptive at K band. This AbFSS structure can be easily achieved in Engineering and be a good candidate for the antenna radome.

Abstract: A FSS-absorber radome with both transmissive and absorptive bands is proposed in this paper. The transmissive band is at X band and the absorptive band is at K band. The radome consists of periodical FSS-Absorber units. Each unit has two layers laminated on a substrate: a metallic layer working as frequency selective surface (FSS) and a resistive layer realizing the absorber function. Firstly, the FSS-Absorber unit is carefully studied. Then this radome-antenna array configuration is researched and simulated. The simulated gain, monostatic RCS and bistatic RCS results of a radome-4x4 patch antenna array model are compared with these simulated results of a 4x4 patch array model. These results indicate that the radome is transparent in its passband and can largely absorb the incoming electromagnetic wave in its absorptive band. The radome can be easily realized in engineering.

Abstract: The processing methods, strengthening methods, water-proof coating procedures, and some ways to improve the transmission of microwaves have been reviewed in relation to fused silica ceramics and their composites for radome applications. Fused silica ceramics are characterized by a residual porosity (up to 18%), low dielectric constant (3.06-3.32), low loss tangent (0.00053-0.0065), excellent thermal properties, but low mechanical strength (37-65 MPa). To achieve higher mechanical strength and better transmission efficiency, new randome materials would be those engineered composites consisting, for instance, of a dense layer-porous core structure, a continuous fiber reinforcement, a multilayered structure, and/or frequency selective surface (FSS) layer (s)/metamaterials.

Abstract: Based on four-terminal network theory, a multilayered model for reflective electrical thickness measurement system is presented in this paper. Using the simulation method of finite element, two crucial parameters of the measurement system are given. One parameter is the distance between the inner surface of composite and reflective mold, the other is the outer surface of composite and horn antenna aperture. This work will guarantee the design of the electrical thickness measurement system of composite.

Abstract: Radomes are adopted to ensure internal antenna systems work normally in severe environments. However, the presence of a radome will adversely affect the electricity performance of the enclosed antenna. A reasonable pre-process of the radome model is a prerequisite for completing electricity performance analysis successfully. Aiming at the difficulties of the design and assembly of curved surface parts, this paper presents a method of modeling and pre-processing by using Pro/E, Ansys and Ansys Workbench to extract element and node information effectively from the finite element model of the radome.

Abstract: Recently, ceramic composites with low dielectric constant, low loss tangent, high flexural strength and high thermal shock resistance have received a considerable attention as candidate materials for certain high speed radome. In this paper, Si₃N₄-BN ceramic composites were fabricated by dry-press processing and cold isostatic pressing, with α-Si₃N₄ and BN as starting powder, Al₂O₃ and Yb₂O₃ as sintering additives, PMMA as pore-forming agen_{Subscript text}t. After sintering for 2 h at 1750°C, porous Si₃N₄-BN ceramic composites with a three-point bending strength of 50~120MPa and a dielectric constant of 3.2~4.4 at 7~18 GHz frequency were obtained. The sintered body was mainly β-Si₃N₄ grains; BN was dispersed in the grains. The formation of β-Si₃N₄ grains was demonstrated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. Furthermore, the influence of the BN content on the dielectric and mechanical properties was also studied. The porous Si₃N₄-BN ceramic composites showed a lower dielectric constant and shrinkage. For above excellent properties, Si₃N₄-BN ceramic composites have been became one of the most hopeful candidate materials for high speed radome.