Antenna Optimization for UAV Platforms Using Characteristic Modes
Jeffrey Chalas, Kubilay Sertel, John L. Volakis
ElectroScience Laboratory, The Ohio State University, Columbus, OH
Long distance data links involving unmanned aerial vehicles (UAVs) are typically done in the 3 – 30 MHz band. That is, such communications utilize ionosphere reflections and atmospheric low-attenuation windows. However, given the small size of UAVs, the physical size of such HF antennas are excessively large, even for antennas that reach the well-known Chu-Harrington limits (L. J. Chu, J. App. Phys, 19, 1163-1175, 1948). Furthermore, such HF antennas are very narrowband and suffer from low radiation efficiency due to their low radiation resistance and inherent conductor losses (R. C. Hansen, Electrically Small, Superdirective, and Superconducting Antennas, Wiley, 2006). As a result, broadband antennas covering the HF to lower-UHF bands are not practical for small UAVs. Separate antenna systems are, therefore, frequently implemented to accommodate the different frequency bands. Beyond the miniaturization challenges, another issue relates to antenna performance when mounted on the UAV platform in the presence of complex materials and other electronics. In this paper, we consider the theory of characteristic modes (CM) (R. F. Harrington and J. R. Mautz, IEEE Trans. AP-19, 5, 622-628, 1971) to significantly improve the radiation behavior of electrically small platform mounted antennas. We examine antenna placement on UAV platforms with the aim to automatically optimize wideband performance and radiation patterns in the HF to lower-UHF bands. This can be achieved through a characteristic mode optimization process that incorporates material and geometry modifications (as well as lumped element loading) at specific platform locations. Since CM calculation is a numerical procedure, limitations presented by the computational speed of off-the-shelf eigen-solvers need be addressed. We will demonstrate efficient procedures for mode tracking that improve computational efficiency and overcome numerical ambiguities. In particular, a broadband, optimized CM design will be presented for a UAV model using FEKO, a commercially available moment method solver.
IEEE Antennas and Propagation Society International Symposium (APSURSI)
2010
July
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