Characterizing near field radiation is a difficult problem, but spectral analysis simplifies the calculation through a Fourier-transform relationship
Characterizing and understanding electromagnetic radiation has been a focal point of research worldwide for more than a century and still remains an important problem today. When analyzing the radiation from an antenna, scientists and engineers are most often concerned with the antenna’s so-called far-field properties. The far-fields are the electromagnetic fields occurring at distances where the antenna approximately appears as a point, i.e. the distance to the antenna is much larger than the overall extent of the antenna. At these distances, the radiated electromagnetic fields behave similarly to plane waves, and analyzing the radiation becomes simplified due to several key approximations. The region of space corresponding to distances much larger than the antenna size is often termed the far-field region, and the distances associated with this region can be extremely far from the antenna depending on its size. While the far-field antenna properties tend to be the primary concern for connectivity or sensing matters, there has been a recent interest in finding the electromagnetic fields at any location in the vicinity, especially in the near-field region close to the antenna. The figure on the right depicts a pedestrian in the near-fields of a large antenna and a satellite in the far-field several miles away. Electromagnetic radiation behaves very differently in these two different regions. My latest contributions have been towards revisiting these theories and modifying the analysis to enable researchers to characterize the absolute near-field values with only the knowledge of the far-field patterns and the radiated power. I worked in a group to integrate a systematic approach to finally give electric field values in V/m to system designers. In a recent collaboration between UCLA and JPL, this approach was used to validate the RapidScat reflector antenna design, which is now operating onboard the International Space Station.
Related Publications
- Antenna measurements through planar near field apparatus: An educational paradigm linking electromagnetic theory, sampling techniques, and FFT
Y. Rahmat-Samii and J. M. Kovitz, “Antenna measurements through planar near field apparatus: An educational paradigm linking electromagnetic theory, sampling techniques, and FFT,” 32nd URSI General Assembly and Scientific Symposium, Montreal, QC, 2017.
- Normalized Plane Wave Spectra: Quantification of Measured Near-Field Distributions for the ISS-RapidScat using Measured Far-field Patterns
Y. Rahmat-Samii, J.M. Kovitz and L.R. Amaro, “Normalized Plane Wave Spectra: Quantification of Measured Near-Field Distributions for the ISS-RapidScat using Measured Far-field Patterns,” in Proceedings of the IEEE Antenna and Propagation Society International Symposium, pp. 1702 – 1703, July 2015.
- Novelties of Spectral Domain Analysis in Antenna Characterizations: Concept, Formulation, and Applications
Joshua M. Kovitz and Yahya Rahmat-Samii, “Novelties of Spectral Domain Analysis in Antenna Characterizations: Concept, Formulation, and Applications,” in Advanced Computational Electromagnetics Methods and Applications, pp.1-82, Artech House, 2015.