Anomalously small retardation of bound (force) electromagnetic fields in antenna near zone

At fundamental level this work uncovers the actually incomplete knowledge of the energy transmission and propagation related to bound (force) electromagnetic (EM) fields. To deal with this problem, we present an experimental approach to a separate study of propagation characteristics of bound and radiation EM fields produced by antennas in a vacuum. A series of our recent experiments continues (J. Appl. Phys., 101 (2007) 023532; 102 (2007) 013529) with improved technical realizations extended for different ultra-high-frequency (UHF) radiation wavelengths. The experimental results show anomalously small retardation of bound EM fields within about the half of the near zone size. Copyright c © EPLA, 2011 EM fields emitted from any antenna have different dependence on the distance in regions close and far from the source. This fact is due to the complex EM field structure which, according to classical electrodynamics (CED), has two components essentially different by nature: velocity-dependent (bound) and accelerationdependent (radiation) fields [1–4]. In static and quasistatic limits, bound contributions are also known as force fields. For antennas with spatial dimensions much smaller than the EM radiation wavelength λ, bound fields are dominant within the near zone (R λ 2π ) whereas EM radiation components prevail in the far zone (R≫ λ 2π ). This difference is clearly used in the vast area of antenna theory and measurements [5], providing main antenna characteristics in terms of only radiation fields. Within the complementary theoretical context of quantum electrodynamics (QED), there are also compelling reasons for distinguishing real photons (quanta of radiation) from virtual photons as carriers of EM interaction. In fact, both real and virtual photons have different properties corresponding to those of classical radiation and bound fields, respectively, since CED represents the classical limit of QED. A particular example shedding light upon the EM field structure is the radiation from an electrically small dipole (a)E-mail: [email protected] antenna [6]. The electric field consists of three terms: p R and ṗ R are due to bound fields, whereas p̈ R is the radiation component. The theoretical studies of the characteristics of the field surrounding the electrically small dipole antenna at a particular time t are well known and the procedure dates back to the pioneer work of Hertz [7] who plotted the electric field lines near the dipole, still resembling those of the electrostatic dipole. As time advances, field lines go away from the dipole with a finite velocity that was observed in Hertz’s early experiments (1888). However, modern texts on classical electromagnetism and the history of physics make no emphasis on the fact that Hertz studied the propagation of the whole EM field with no separation on bound and radiation fields (concepts not available in the XIX century). Moreover, Hertz’s observations of EM waves propagation were effected in the far zone [8], i.e. where radiation is dominant. In fact, Hertz achieved an operating wavelength of about 6m (∼50MHz), starting observation from 1–2m [7]. Nowadays, all typical near-field antenna measurements are designed to provide information on antenna’s far-field patterns (full-size maps of the EM field phase and amplitudes) from their measured near-field data [9]. Thus, neither Hertz at the end of the XIX century nor modern near-field antenna measurements from the early period in the middle of the XX century up to present days made no