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Shaped Radome and Embedded Frequency Selective Surface Modeling for Large-Scale Platforms
Navy SBIR 2016.1 - Topic N161-022 NAVAIR - Ms. Donna Attick - [email protected] Opens: January 11, 2016 - Closes: February 17, 2016 N161-022 TITLE: Shaped Radome and Embedded Frequency Selective Surface Modeling for Large-Scale Platforms TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors ACQUISITION PROGRAM: PMA 290 Maritime Surveillance Aircraft OBJECTIVE: Develop software tool(s) that accurately predicts on-platform electromagnetic interactions with realistic antenna radome covers, including those with an embedded frequency selective surface (FSS). DESCRIPTION: Depending on their design, protective and aerodynamic radome covers can have a significant impact on the installed radiation patterns of the antenna(s) behind them, which is usually deleterious to the application supported by the antenna. This important fact must be considered when new or upgraded antenna systems supporting applications such as high-bandwidth data links, electronic attack (EA), non-cooperative target identification, anti-jamming capability, etc., are being planned for integration under a radome with a new or existing platform. For example, multi-bounce interactions between the antenna and the radome or between different parts of the radome can produce secondary beams and raise sidelobe levels. In addition, radomes can modify an airframe�s radar signature and distort the signature contribution of structures behind them. Furthermore, radomes sometime embed a frequency-selective surface (FSS) layer to filter electromagnetic waves as they pass through their cover. The design of a FSS, combined with the FSS�s conformity to the radome shape, frequently leads to cross-polarization effects and grating lobes that affect radar signatures and installed radiation patterns in complex ways. Current state-of-the-art tools based on ray-tracing techniques are available for predicting installed antenna performance and radar signatures on electrically large airframes (UHF and above) described by realistic 3-D CAD models; however, , their material modeling capabilities, (based on tables of reflection and transmission coefficients for thin dielectric layers), are too simple to accurately model the impact of radomes. For example, the thickness of each radome varies continuously across the radome, requiring a finely grained stair stepping of separate coating tables to capture this variation, and this is extremely difficult to configure in practice. In the case of a FSS radome, the FSS and surrounding radome layers can be simulated as a planar periodic structure to build the table(s) of coefficients. This approach, however, loses important phenomenology, such as distortion and truncation of the FSS lattice when applied to the actual radome structure. Further, such tables must strip out any information about cross-polarization scattering and grating lobes generated by the planar FSS simulation code because the ray-tracing codes are powerless to exploit this information, at least in current practice. Often, the problem boils down to insufficient geometric characterization, since exploiting this additional information requires knowledge of how the FSS elements are oriented within the radome and somehow communicating this to the ray-tracing code. An innovative approach is needed to modeling radomes and FSS radomes in ray-tracing codes that can account for variable thickness, cross-polarization, grating lobes, and other higher-order effects. This approach must be able to exploit detailed information generated by rigorous simulation of the periodic FSS structure, and do so in such a way that can properly account for deformation and truncation of the FSS lattice when applied to realistic radome shapes. Successful applicants will demonstrate access to mature and proven ray-tracing technology for solving installed antenna and radar signature problems on general high-resolution structures, particularly large-scale airframes, including the rights to modify these tools, in order to eventually integrate the new algorithms. As part of the solution, the tool user must be able to visualize the radome and its deformed FSS lattice within the Graphical User Interface (GUI), and the user must have simple controls for adjusting the deformation and truncation details. It is also important that such modeling and visualization capability be incorporated in a proven and mature ray-tracing tool that can solve general-purpose installed antenna and radar signature problems on realistic airframe CAD models. The capability must be able to handle problems of antennas and arrays located behind radomes while capturing interactions with the rest of the platform. PHASE I: Develop and demonstrate asymptotic ray-tracing algorithms for modeling radomes of continuously varying thickness, with and without FSS layers, that address the modeling deficiencies. Identify an existing FSS code or full-wave solver that is well suited to provide higher-order effects data on the FSS to feed these new algorithms. Demonstrate that the new algorithms can exploit these higher-order outputs, such as cross-polarization scattering coefficients and additional propagating modes (i.e., grating lobes). Cross-validate these new algorithms with explicit, full-wave solutions on suitably scaled problems while additionally demonstrating how these new techniques could be integrated with these tools to solve the large-scale problem (e.g., radomes positioned in front of an antenna and attached to a full-scale aircraft). PHASE II: Develop a prototype tool or tools for predicting radiation patterns of antennas/arrays behind radomes and their radar signatures. The tool(s) should interface to a functioning FSS code or full-wave solver for simulating the planar periodic lattice and that is delivered with the tool(s). Implement the tool(s) with a GUI for problem setup. The GUI design should emphasize ease-of-use in the context of configuring and visualizing arbitrary radome shapes. Also develop and implement an algorithm within the same tool(s) for conforming an FSS lattice to the radome. The tool should provide simple controls for adjusting the deformation and truncation of the FSS lattice while providing 3-D visual feedback on the conformed lattice. PHASE III DUAL USE APPLICATIONS: Integrate the FSS/radome simulation capability developed in Phase II with a robust ray-tracing tool(s) for predicting installed radiation patterns and radar signatures of general 3D structures described by high-fidelity CAD models. The integrated tool(s) should support simulations of realistic airframes with one or more antennas or arrays located behind radomes. The technology developed under this topic will provide significant modeling-and-simulation benefits to a variety of commercial and military applications wherever antennas and arrays are installed behind radomes on platforms, including aircraft, ships, spacecraft, and fixed installations. The resulting tool(s) will also be invaluable in advanced radome and FSS radome design. REFERENCES: 1. Munk, B. A. (2000). Frequency Selective Surfaces, Theory and Design. New York: Wiley. Retrieved from http://onlinelibrary.wiley.com/book/10.1002/0471723770 2. Ling, H., Chou, R., & Lee, S. W. (February 1989). "Shooting and bouncing rays: calculating the RCS of an arbitrarily shaped cavity," IEEE Trans. Antennas Propagat., Vol. 37, No. 2, p. 194-204. Retrieved from http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=18706 3. Chew, W. C. (1990). Waves and Fields in Inhomogeneous Media. Van Nostrand Reinhold. 4. Kozakoff, D. J. (1997). Analysis of Radome-Enclosed Antennas. Norwood, MA: Artech House. 5. Kim, J. H., Chun, H. J., Hong, I. P., Kim, Y. J., & Park, Y. B.(2014). "Analysis of FSS radomes based on physical optics method and ray tracing technique". IEEE Antennas and Wireless Propagat. Ltrs. Vol. 13, p. 868-871. Retrieved from http://ieeexplo KEYWORDS: Modeling And Simulation; Antenna; Computational Electromagnetics; Radar Signature; Radome; Frequency Selective Surface TPOC-1: 631-673-8176 TPOC-2: 301-342-2637 Questions may also be submitted through DoD SBIR/STTR SITIS website.
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