Unified theory of near-field analysis and measurement: Nonmathematical discussion

A new unified theory of near-field analysis and measurement emphasizes highly accurate, extremely efficient data processing to yield, e.g., radiation, receiving, and scattering patterns, and absolute gain values. The theory includes 17 types of plane rectangular and plane radial scanning, a more accurate and efficient plane polar scanning, spherical scanning, various types of circular cylindrical scanning, many procedures for determining complex dyadic scattering patterns, the extrapolation method for gain and effective area, and application of symmetry analysis to scattering and inverse scattering analysis. High accuracy is obtained by expressing the fields as linear combination of exact solutions of the differential equations involved (Maxwell's in the electromagnetic (EM) cases) and by using exact expressions for their transformations under coordinate changes. High efficiency is obtained with natural orthogonalities of both the solutions and transformation coefficients with respect to integration, especially summation, and implemented with the fast Fourier transform (FFT) as an approximation-free symmetry decomposition. The unified theory is based upon relativistic and gauge invariances, symmetry analysis, and the scattering matrix theory; it yields all the preceding facets and systems, both electromagnetic and scalar, and the single unified notation, general equations, and explicit expressions for the quantities which vary with the physical or scanning system. A nonmathematical discussion of other papers on the theory is provided. Many of the conceptual errors of the literature are corrected. The advantages and limitations of near-field measurements are described, and scanning systems are compared.