April 22, 2022
Colloquium Topic: Ray and Wave Optical Methods for Solving Large EM Radiation And Scattering Problems
Ray and Wave Optical methods provide tools for solving short wavelength electromagnetic (EM) radiation and scattering problems in engineering applications. At moderate to high frequencies, the EM fields exhibit a highly local character, namely, waves can be tracked “locally” as plane waves along incident, reflected and diffracted ray paths, etc.. Thus ray methods offer vivid physical insights into the radiation and scattering mechanisms which in turn provide valuable information to design engineers. The diffracted rays were intoduced by Keller in his Geometrical Theory of Diffraction (GTD) via systematically extending Geometrical Optics (GO) concepts. In its original form the GTD exhibits discontinuities or singularities within ray shadow boundary and caustic (focal) transition regions; therefore, in practice, a uniform version of the GTD, e.g., the UTD which overcomes ray discontinuities and singularities must be used. Within transition regions containing a confluence of both shadow boundaries and caustics, the UTD exhibits singularities and it must generally be augmented there by wave optical methods such as the Equivalent Current Method (ECM), Physical Optics (PO) or its refinements, namely the Iterative Physical Optics (IPO), or the Physical Theory of Diffraction (PTD). The UTD is a ray technique while PO, IPO, PTD and ECM require an integration over high frequency currents on the radiating object; thus the wave optical methods are less efficient. Furthermore, exact series solutions or numerical solutions to exact governing integral equation (IE) or partial differential equation (PDE) formulations can become rapidly cumbersome and even intractable at high frequencies. Some applications of the above methods to treat large antenna/scattering problems will be presented.
Colloquium Speaker: Prabhakar Pathak
Prabhakar H. Pathak received his Ph.D. (1973) from The Ohio State Univ.( OSU), in the Dept. of ECE. Currently, he is Prof. Emeritus at OSU. He was also an Adjunct Prof. at the Univ. of South Florida. He is regarded as a co-developer of the Uniform Geometrical Theory of Diffraction (UTD). His interests are in the development of Ray, Wave, and Beam optical methods in frequency (and time) domains, for solving electrically large antenna and scattering problems of engineering interest. He has also developed some Hybrid methods which combine the best features of any of the above methods with numerical methods to solve electromagnetic (EM) problems which cannot otherwise be solved in a tractable fashion by any of the methods when used alone. His work is specifically applicable to the prediction of EM radiation and coupling associated with small antennas, or large phased array antennas, placed on or near large structures (e.g. on airborne, spaceborne or naval platforms) as well as to the EM scattering by such structures. He has presented many invited lectures in the USA and abroad; also he has published 7 book chapters and several journal and conference papers. Recently he has authored a book with R. J. Burkholder (co author) entitled Electromagnetic Radiation, Scattering and Diffraction. He was an Assoc. Ed. for IEEE Trans. AP; an IEEE AP distinguished lecturer (DL) during 1991-1993; chair of that DL program (1995-2005); member of IEEE AP-S AdCom (2010). He received the 1995 IEEE AP Schelkunoff best paper award, the 1996 George Sinclair Award from the OSU ElectroScience Lab, the 2009 ISAP best paper award, the IEEE 3rd Millennium Medal from AP-S, and the 2013 IEEE AP-S Distinguished Achievement Award. He is a Life Fellow of IEEE and member of URSI Commission B.