Over the last year, I have been collaborating with Prof. Rahmat-Samii on a project with JPL related to the characterization of radiation in the near field zone of large antennas, such as reflector dish antennas. Our goal was to quantify the absolute magnitudes of the electric field distributions in their respective V/m values. Our approach relies on the spectral theory of radiation, which has often been termed the Plane Wave Expansion technique. The beauty of this approach is that one can relate electromagnetic fields on a plane by a Fourier transform operation F, as depicted in the figure below.
The Plane Wave Expansion allows us to relate fields on a plane by a Fourier transform F. We can also relate the Plane Wave Spectrum to the far-field distributions, giving us the link we need to characterize the near-fields.
Previously, researchers were mainly interested in relative distributions of the near-fields, and they used this technique to quantify the relative values. Our primary contribution is in modifying the calculations to give the exact electric field values in V/m, which rely on an FFT calculation. We recently published a book chapter that outlines the systematic procedure one might take to efficiently characterize the near-field distribution using the Plane Wave Spectrum using only the far-field patterns and radiated power. This has important applications for measurements, where knowledge of the measured far-field patterns and radiated power could be used to validate near-field levels which were previously estimated through simulation. The chapter was entitled “Novelties of Spectral Domain Analysis in Antenna Characterizations: Concept, Formulation, and Applications” and was included in the book Advanced Computational Electromagnetics Methods and Applications. The book was published by Artech House, Inc and can be found here.