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This paper presents a theory of the time-domain radar cross section (RCS) of objects in discrete random media. The time-domain formula is obtained by applying the inverse Fourier transform of the t...

On October 13, 2019 is the ninetieth birthday of the renowned physicist Professor Valerian I. Tatarskii. He is one of the founders of the international journal Waves in Random and Complex Media and...

Second order statistical moments of scattered electromagnetic waves in the turbulent magnetized plasma slab with electron density fluctuations are calculated applying the modify stochastic smooth perturbation theory and the boundary conditions. The obtained results are valid for arbitrary correlation function of electron density fluctuations. Stokes parameters are analyzed both analytically and numerically. The theory predicts that depolarization effect caused by second Stokes parameter may be important in scintillation effects. Numerical calculations are carried out for new spectral function of electron density fluctuations containing both anisotropic Gaussian and power-law spectral functions using the experimental data. Polarimetric parameters are calculated for different anisotropy factor and inclination angle of elongated small-scale irregularities with respect to the magnetic lines of forces. The relationship between the scintillations and the polarimetric parameters is important. Web of Science 8 2 84 77

Statistical characteristics of scattered electromagnetic waves in the turbulent magnetized plasma caused by electron density fluctuations are calculated using complex geometrical optics approximation taking into account both diffraction effects and polarization coefficients. Scintillation level normalized on the variance of the phase fluctuations is analyzed analytically and numerically for small-scale plasma irregularities using the experimental data. New properties of the electromagnetic wave scintillations have been revealed. It is shown that splashes arise in the ionosphere leading to the turbulence and generation of new oscillations (waves and/or Pc pulsations) propagating in space and the terrestrial atmosphere. Turbulence extending in the lower atmospheric layers can influence on the meteorological parameters leading to climate change. Web of Science 81 165 159

We present a physics-based channel matrix that establishes the connection between electromagnetism and information theory. The approach is based on impedance matrices and related to the scattering matrix formulation. Cavities and random media support a wave chaotic behaviour that yields an exponential proliferation of multiple paths due to the presence of multiple reflection or scattering. It is shown that fading can be included using the random coupling model (RCM). This model leads to theoretical and numerical predictions of the probability density function of the mutual information in large and complex electromagnetic environments. The effect of losses and modal density on channel capacity can thus be explored and channel hardening bounds quantified.

The ionosphere is greatly influenced by ionizing radiation including both electromagnetic flux and energetic particles. The ionosphere is immersed in a magnetic field and the interactions of radio waves with the ionosphere are complex and exhibit the following properties: anisotropy, absorption, dispersion, birefringent. The ionospheric effects on radiowave systems depend upon the focus of the treatment. The development of inhomogeneous electron density structures is responsible for radiowave signal fluctuations. A comprehensive treatment of radiowaves propagation in the ionospheric plasma is based on the investigation of the statistical moments of both amplitude and phase fluctuations of scattered radiation. In this paper analytical calculations of the statistical characteristics in the conductive collision magnetized ionospheric plasma have been carried out for the first time using the complex geometrical optics approximation. Stochastic wave equation of the phase fluctuations includes both dielectric permittivity and conductivity tensors which are random functions of the spatial coordinates and time. Using the boundary conditions correlation function of the phase fluctuations has been obtained for arbitrary second order statistical moment of electron density fluctuations (large and small ionospheric plasmonic structures); observation points are spaced at small distance. The index of refraction contains both ordinary and extraordinary waves. Angular power spectrum (broadening, shift of its maximum) of scattered electromagnetic waves is investigated. It was shown that Hall’s, Pedersen, and longitudinal conductivities have a substantial influence on the frequency fluctuation of an incident wave. Doppler spread associated with random ionospheric structure, and Doppler shifts associated with relative motion of the ray path with respect to the elongated plasmonic structures. Spatial-temporal broadening of the spatial spectrum depends on the anisotropy factor of elongated plasma irregularities, inclination angle with respect to the lines of forces of geomagnetic field, collision frequency between plasma particles, conductivity fluctuations, and the movement of ionospheric plasmonic irregularities. Shift of the spectral maximum changes the sign depending on the anisotropy factor of elongated plasma irregularities, inclination angle with respect to the lines of forces of geomagnetic field and conductivity fluctuations. Numerical calculations and spatial-temporal modeling are carried out for both large and small-scale ionospheric plasma irregularities using experimental data and experimentally observing power-law spectrum of electron density fluctuations. The obtained results are useful for solving the reverse problem restoring plasma parameters, in satellite communication and navigation systems that operate in the earth-space regime. The influence of the conductivity fluctuations on the second order statistical moments will open new horizons in understanding and forecasting new phenomena in the upper ionosphere caused due to spatial-temporal parameters fluctuations.

Statistical characteristics of scattered ordinary and extraordinary electromagnetic waves in the magnetized plasma are considered using the smooth perturbation method. Diffraction effects and polarization coefficients are taken into account. Second order statistical moments of scattered radiation are obtained for arbitrary correlation function of electron density fluctuations. Broadening of the spatial power spectrum and displacement of its maximum, wave phase structure function and the angle-of-arrivals are obtained for three-dimensional spectral function containing anisotropic Gaussian and power-law spectral functions. Scintillation level of scattered radiation is analyzed for different parameters characterizing anisotropic plasma irregularities for the ionospheric F-region. The spectral widths (first and second moments) of the power spectrum and scintillation periods are calculated for “frozen-in” drifting elongated plasma irregularities using the experimental data.

The technology of “through-the-wall radar imaging” enables seeing through walls by reconstructing the image based on backscattered waves passing through an optically opaque dielectric wall. However, when the electromagnetic waves cannot penetrate the shielding walls (such as metallic walls), a problem called “hard-wall radar imaging” (HWRI) must be investigated. As the objects are located in the shadow region, where only the diffracted field can be reflected back via edges, conventional imaging techniques are not applicable. The HWRI problem is an imaging scenario with an intrinsic multipath of signal propagation. Therefore, it has been studied using a model-based time-reversal (TR) decomposition of TR operator imaging method. In this paper, an imaging technique with a distributed transmitting and receiving array is proposed as a robust way resolving the problem with a low signal-to-clutter ratio in TR imaging. In this method, the interelement response matrix is collected for the construction of the covariance matrix, from which the geometry of the hard wall is determined from the direction of arrival by the multiple signal classification techniques. Next, the adaptive interference cancellation technique is applied to suppress the interference terms in the image function due to the multipath effects. The experimental results were obtained from a distributed multiple-input multiple-output radar system and show that this method is useful not only for the detection of a weak object echo but also for the localization of multiple targets hidden behind the wall.

Second order statistical moments of the phase fluctuationsare obtained taking into account the boundary condition,diffraction effects and polarization coefficients of theordinary and extraordinary waves. The variance and thecorrelation function are calculated for arbitrary 3D spectralfunction of electron density fluctuations containing bothanisotropic Gaussian and power-law spectra; anisotropycoefficient and the orientation angle of elongated plasmairregularities. The phase scintillation index and thescintillation level are analyzed numerically. Maximum ofthe scintillation index for small-scale irregularities is in theinterval 0.2-0.3 corresponding to the moderate scintillationintensity, within the weak-scatter regime. Splashes arerevealed for different anisotropy factor of elongated largescaleirregularities varying orientation angle with respect tothe lines of force of geomagnetic field. Scintillation index iscalculated for small-scale irregularities using the “frozenin”assumption and taking into account movement of rigidirregularities. Log-log plots of the power spectrum of theintensity fluctuations have the same minimums satisfyingthe “standard relationship” of scattered ordinary andextraordinary waves. It was shown that the normalizedscintillation level growth in both non-fully-developeddiffraction pattern and in transition zone increasinganisotropy factor. Rising orientation angle scintillation leveldecreases and splashes arises in fully developedscintillation region.

This paper gives a summary of the key research developments of electromagnetic waves in random media during the past 100 years, emphasizing the statistical multiple scattering theories applied to geophysical remote sensing and imaging of biological media by electromagnetic, optical, and ultrasound waves. This summary also includes considerations of integration of random media theories and signal processing. Radiative transfer theories have been extensively applied to remote sensing, imaging, and detection; recent developments include coherent effects in multiple scattering, acoustic multi-physics, and time-reversal imaging. This paper concludes with a discussion of possible future studies and research development.

General dispersion equation is obtained at arbitrary inclination angles of the external magnetic field and wave vector of an incident EM wave. Statistical characteristics of the phase fluctuations of scattered high frequency EM waves in the collision magnetized plasma caused by electron density and external magnetic field fluctuations taking into account polarization coefficients for both ordinary and extraordinary waves are calculated analytically. The influence of collision frequency, anisotropy factor and angle of inclination of prolate irregularities of electron density fluctuations with respect to the geomagnetic field of lines on the broadening of the spatial power spectrum is analyzed. Phase portraits of the phase fluctuations caused by the geomagnetic field fluctuations are constructed at different spatial parameters characterizing magnetic field and electron density fluctuations. Numerical calculations are carried out for the ionospheric F -region parameters using experimental data.

This chapter discusses some of the fundamentals of metamaterials including transformation electromagnetics (EM) and cloaking. Most encountered materials in practice have relative permittivity greater than one, except plasma whose relative permittivity is less than one, and relative permeability equal to one, except magnetic materials. Artificial magnetic materials have magnetic properties not found in nature even though the materials are nonmagnetic. Split‐ring resonators (SRRs) are a typical example. A man‐made chiral material consisting of a collection of metal helices is another example. The chapter also discusses another example that is bianisotropic media. SRR has been studied for use in magnetic resonance. Its size can be small and can be used as a homogeneous medium. The chapter further discusses a new and different application of the coordinate transformation, not for producing a new material, but for using the transformation to solve a wave scattering problem. Finally, it considers a wave propagating over a rough surface.

This chapter reviews the fundamental definitions and formulations related to antennas, aperture antennas, linear antennas, and arrays. The most useful measures of antenna characteristics are directivity and gain. The exact current distributions on an antenna such as a wire antenna must be determined by solving the complete boundary value problem. In many practical antennas, the approximate current distributions are known based on more exact calculations or on experimental data. The chapter presents the radiation field due to given current distributions. It gives some examples of the radiation fields of known current distributions based on the formulation. Current distribution on a wire antenna is approximately sinusoidal. The chapter considers microstrip antennas that are made of a thin patch of metal on a grounded dielectric slab. Thus, it can be viewed as a half‐wavelength transmission‐line cavity with open terminations at both ends where the power leaks out.

This chapter discusses the characteristics of porous media and seismic coda waves. One of the important examples of a porous medium is oil shale. One is the permittivity and conductivity of the porous medium as given by Archie's law. The other is the flow of liquid such as oil through the porous medium as given by Darcy's law and "fluid" permeability, which is different from the "magnetic" permeability concept we commonly use in electromagnetic studies. The study of porous media is closely related to the "percolation theory" and the "fractal". The permeability of a porous medium such as shale is a measure of the resistance to the flow of a fluid through the medium. The chapter shows typical seismic waves observed at the receiver. The study of the P‐coda, S‐coda, and Rayleigh‐coda is critical to the understanding of the total seismic radiation.

Many bodies of practical interest may be closely approximated by cylindrical structures, spheres, and wedges. The scattering and absorption characteristics of these bodies are important in many practical problems. This chapter investigates the scattering of waves from these objects and the effects of these structures on the radiation characteristics of antennas. It presents a number of powerful analytical techniques, including the Fourier transform, saddle‐point technique, Watson transform, residue series representation, and geometric optical solutions. The chapter also investigates the radiation from an axial dipole located near the conducting cylinder. One of the important characteristics of antennas is the radiation pattern, the behavior of the field at a large distance. It is important to develop an alternative representation that may be useful in describing waves for more practical and complex shapes. The Watson transform technique offers this alternative representation which may be used for more complex problems.