TECHNOLOGY AREAS: Information Systems, Ground/Sea Vehicles, Sensors, Electronics

OBJECTIVE: Develop and demonstrate effective design tools for optimizing the electromagnetic radiation efficiency of military platform integrated antennas.

DESCRIPTION: There is interest in improving the performance of vehicular antennas in the HF through lower UHF bands (i.e., 2 MHz through 450 MHz). At the same time, there is a desire to reduce the visual signature of the antennas. Newman showed that the radiation efficiency of a small antenna, mounted on a structure, could be increased substantially by positioning it appropriately. In essence, the antenna functions as a probe that excites currents on its supporting structure. The position of the probe is chosen to induce currents that produce the desired response in terms of some predefined performance criteria, such as power gain or radiation pattern.

More than one location may be necessary in order to meet the criteria over a given frequency band. Some locations may result in substantial improvements in radiation efficiency, while others may result in little or no improvement. A second and related problem is the selection of an operating frequency which optimizes the radiation efficiency. The optimum location at one frequency may not be the optimum at another frequency. The antenna designer may not have complete freedom in selecting location and frequency. However, how the efficiency varies with frequency and location can help in the design of an optimal military platform integrated antenna.

For some simple configurations, the optimum positions might be determined merely by examining the approximate current distribution on the platform. However, in general the optimum probe position is not obvious. The focus of this topic is the development and demonstration of effective design tools for optimizing military platform integrated antennas. There may be several possible approaches to this development. However, the Method of Characteristic Modes, first described by Garbacz and then refined by Harrington and Mautz, may prove to be useful. The determination of Characteristic Modes may involve considerably less computation and also give more physical insight. The Characteristic Modes are real currents on the surface of a conducting body. The Characteristic Modes have orthogonality of the radiated fields. Associated with each Characteristic Mode is an eigenvalue. The eigenvalues are important because the radiation of a particular Characteristic Mode is indicated. In order to improve substantially the efficiency of an antenna mounted on a military platform it is necessary to excite modes which are effective radiators. The use of the Method of Characteristic Modes would be most applicable where the platform is not electrically large. As the electric size of the support structure increases, more and more characteristics modes are effective radiators. In this case, the exact antenna location and operating frequency is likely to be less critical.

PHASE I: Assemble a preliminary design framework for optimizing the electromagnetic radiation efficiency of a military platform mounted antenna. Perform a preliminary evaluation of the design tools to demonstrate utility.

PHASE II: Develop the user-oriented design tools for optimizing the electromagnetic radiation efficiency of a military platform mounted antenna. Demonstrate the utility of the design tools with application to military platforms with special emphasis on HF through UHF antennas on USMC platforms.

PHASE III: Dual Use Applications: This effort will provide an important foundation for optimizing the performance of platform embedded antennas in appropriate frequency bands.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The focus of this topic is the development and demonstration of effective design tools for optimizing military platform integrated antennas. This value of this capability is not limited to military platforms. As indicated in the professional publications, antenna engineers are attempting to address antenna integration in a wide variety of commercial platforms, including automobiles, trucks, boats and airplanes. This topic could provide a capability that would substantially improve antenna engineering for both military and commercial applications.

REFERENCES:
1. Austin, B. A. and K. P. Murray, "The Application of Characteristic-Mode Techniques to Vehicle-Mounted NVIS Antennas," IEEE Transactions on Antennas and Propagation, AP-40, February 1998.

2. Harrington, R. F. and J. R. Mautz, "Theory of Characteristic Modes for Conducting Bodies," IEEE Transactions on Antennas and Propagation, AP-19, September 1971.

3. Harrington, R. F. and J. R. Mautz, "Computation of Characteristic Modes for Conducting Bodies," IEEE Transactions on Antennas and Propagation, AP-19, September 1971.

4. Liu, D., R. J. Garbacz and D. M. Pozar, "Antenna Synthesis and Optimization Using Generalized Characteristic Modes," IEEE Transactions on Antennas and Propagation", AP-38, July 1992.

5. Newman, E. H. "Small Antenna Location Synthesis Using Characteristic Modes", IEEE Transactions on Antennas and Propagation," AP-27, July 1979.

6. Rockway, J. D. , Y. Kuga, and A. Ishimaru, S. T. Li, C. W. Manry, J. W. Rockway, "Resonant Confocal Imaging (RCI) of Resonant Spatial Current Modes of Structures in the Resonant Region," National Radio Science Meeting, Boulder, Colorado, January 1999.

7. Wu, W, B-Z Want, X-S Yang and Y. Zhang, "A Pattern-Reconfigurable Planar Fractal Antenna and its Characteristic-Mode Analysis," IEEE Antennas and Propagation Magazine, June 2007.

KEYWORDS: Computer-Aided Design; Computational Electromagnetics Antennas; Characteristic Modes; antenna-platform coupling; RF radiation; antenna efficiency

TPOC: Diana Arceo
Phone: (619)553-6344
Fax:
Email: [email protected]
2nd TPOC: John Moniz
Phone: (703)696-2492
Fax:
Email: [email protected]