Electronic Military & Defense Annual Resource

6th Edition

Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.

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Techniques and arbitrary combinations of those in a cable bundle. Cable bundles can include braided or solid tubular shields. In Figure 5, a cable bundle consisting of several wires has been routed slightly above the metal bottom of the helicopter. For a realistic analysis, large parts of the helicopter are made not of metal but of carbon-fiber-reinforced composite material or glass. In a schematic environment, the cables have been terminated with resistors. Instead of resistors, more-general RLC circuits, Touchstone files, or SPICE netlists could also have been applied. The blade antenna on top of the rotorcraft is transmitting 30 W of power, some of which enters the helicopter and interferes with the systems. The lower graph shows the voltages delivered to the cable terminals as a function of rotor angle. Depending on the system and the specifications, the design engineer can evaluate how much shielding to apply to the cable bundle. Radar Cross Section (RCS) For studies of rotorcraft visibility to radar, two regimes are of interest. Over-the-horizon HF radar, operating with wavelengths of 10-100 m, may excite the blades and detect a distinct modulation on the reflected signal 6 that makes it stand out from clutter. To analyze this situation, the MoM with Numerical Green's Function is well-suited. On the other hand, radar operating in the GHz range is more likely to observe narrow reflection spikes from large faces or complicated reflections due to multiple bounces inside the air frame. Since the radar wavelength is short relative to the target size, asymptotic methods are most suited. PO often is used for a quick look, while RL-GO, with multiple reflections, provides a more thorough analysis (Figure 6). If needed, asymptotic methods can be hybridized with rigorous ones (e.g., to analyze the RCS of engine air inlets). Propagation The study of flight scenarios and link budgets in a complicated terrain with hills and vegetation requires dedicated propagation analysis software that can handle the large geometries involved. Figure 7 depicts a coverage map in mountainous terrain, and the coverage was determined with the dominant path model (Altair's winProp 7 software was used in the creation of this example). This method determines rapidly which propagation path between the transmitter and any location will be the dominant one — a faster approach than a full analysis of all possible ray paths. Reflections and diffractions are included. Conclusions Rotorcraft encounter many environmental electromagnetic challenges. The impact of the rotating blades on antenna patterns, antenna coupling, interference, and radar visibility compound the engineering challenges. However, various simulation methods, properly applied, can help to overcome each of these challenges in an efficient manner. n References 1. FEKO, Comprehensive Electromagnetic Analysis Software Suite (part of Altair HyperWorks), www.altairhyperworks.com/FEKO. 2. U. Jakobus, Overview of Hybrid Methods in FEKO: Theory and Applications, 2010 International Conference on Electromagnetics in Advanced Applications (ICEAA), pp. 434- 437 3. A.C. Polycarpou, C.A. Balanis, and A. Stefanov, Helicopter Rotor-Blade Modulation of Antenna Radiation Characteristics, IEEE Trans. Ant. Propagat., Vol. 49, No. 5, pp. 688-696, May 2001. 4. M.S. Reese, C.A. Balanis, C.R. Birtcher, and G.C. Barber, Modeling and Simulation of a Helicopter-Mounted SATCOM Antenna Array, IEEE Antennas and Propagation Magazine, Vol. 53, No. 2, pp. 51-60, April 2011 5. U. Jakobus, M. Bingle, W. Burger, D. Ludick, M. Schoeman, and J. van Tonder, Method of Moments Accelerations and Extensions in FEKO, 2011 International Conference on Electromagnetics in Advanced Applications (ICEAA), pp. 62-65 6. P. Pouliguen, L. Lucas, F. Muller, S. Quete, and C. Terret, Calculation and Analysis of Electromagnetic Scattering by Helicopter Rotating Blades, IEEE Trans. Ant. Propagat., Vol. 50, No. 10, pp. 1396-1408, October 2002 7. WinProp V13, Altair Engineering, Inc., www.altairhyperworks.com/winProp. Electronic Military & Defense Annual Resource, 6th Edition 12 Figure 6: Radar cross section determined with ray-launching geometrical optics Figure 7: Transmitter coverage in a mountainous terrain determined with the Dominant Path Model Dr. Martin Vogel is principal application engineer at Altair Engineering, Inc. He earned his M.S. in physics from Leiden University and his Ph.D. in electromagnetics from Delft University of Technology, both in the Netherlands. From 1985 through 1996, he worked for TNO Defense and Security, a Dutch defense contractor. In 1996 he had a one-year assignment at Kirtland Air Force Base in New Mexico. From 1996 until 2011 he worked for ANSYS (Ansoft until 2008) as a senior application engineer and in several other roles, followed by a sabbatical abroad. Dr. C.J. Reddy is vice president business development- electromagnetics, Americas at Altair Engineering, Inc. He received his Ph.D. in electrical engineering from the Indian Institute of Technology, Kharagpur, India. Dr. Reddy was a research associate at NASA Langley Research Center and previously a research fellow at the Natural Sciences and Engineering Research Council (NSERC) of Canada. Dr. Reddy also is president of Applied EM Inc., a senior member of IEEE and AMTA, and the publisher of 35 journal papers, 54 conference papers, and 17 NASA Technical Reports, to date.

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