Andrey Osipov

Mono- and Bistatic Scattering Reduction by a Metamaterial Low Reflection Coating

Significant reduction of mono- and bistatic scattering cross sections of an electrically large metallic cube through the application of an electrically thin metamaterial low reflection coating operating in the Ka-band (30-40 GHz) is described. A coating composed of a metallic array of sub-wavelength sized capacitively loaded strip inclusions printed on top of a thin, slightly lossy and grounded substrate has been designed and fabricated to experimentally evaluate the performance of the coating in scattering reduction. The scattering reduction is estimated by comparing the mono- and bistatic scattering patterns of the coated and uncoated cube. The measurement results are compared with full wave and physical theory of diffraction simulations, and the possibility of accurately modeling the low reflection coatings with impedance boundary conditions is pointed out.

Experimental Characterization of a Broadband Transmission-Line Cloak in Free Space

The cloaking efficiency of a finite-size cylindrical transmission-line cloak operating in the X-band is verified with bistatic free space measurements. The cloak is designed and optimized with numerical full-wave simulations. The reduction of the total scattering width of a metal object, enabled by the cloak, is clearly observed from the bistatic free space measurements. The numerical and experimental results are compared resulting in good agreement with each other.

Bistatic scattering characterization of a three-dimensional broadband cloaking structure

Here we present the results of full experimental characterization of broadband cloaking of a finite-sized metallic cylinder at X-band. The cloaking effect is characterized by measuring the bistatic scattering patterns of uncloaked and cloaked objects in free space and then comparing these with each other. The results of the measurements demonstrate a broadband cloaking effect and are in good agreement with numerical predictions.

A simple approximation of the Maliuzhinets function for describing wedge diffraction

A new approximation of the Maliuzhinets function /spl psi//sub /spl Phi//(/spl alpha/) by a single cosine function is proposed. This is the simplest approximation of the function available in the literature. The use of the cosine approximation permits representing fields scattered by nonmetallic wedges in terms of elementary functions only. The accuracy of the approximation, as applied to the case of an impedance wedge under normal illumination, is estimated both analytically and numerically.

Mechanisms of high-frequency scattering from impedance bodies with unit relative surface impedance

Characteristic features of electromagnetic scattering from electrically large bodies with the surface impedance equal to the wave impedance of the surrounding medium are described. It is shown that such value of the impedance significantly reduces not only the specular reflection but also the diffraction contributions from creeping and edge-diffracted waves.

Physical theory of diffraction for scatterers with low reflection surface

Scattering from bodies with the surface impedance matched to the wave impedance of the surrounding medium is particularly weak. The corresponding impedance surface is referred to as the low reflection surface. The paper describes application of the physical theory of diffraction to the simulation of scattering from electrically large low reflection bodies. Since the main specular contribution is low, the focus is on accounting for corrections due to the edges in the scattering surface.

An Improved Image-Based Circular Near-Field-to-Far-Field Transformation

An improved version of the near-field-to-far-field transformation (NFFFT) for determining the radar cross section (RCS) of electrically large targets from the scattered field measured with a monostatic radar over a circle in the near field of the targets is presented. The characteristic feature of the proposed NFFFT is an improved imaging operator which is derived by requiring that the integral transformations involved in the NFFFT scheme be self-consistent for every electrically small scatterer. The presented NFFFT version is expected to lead to more accurate RCS values for strongly asymmetric targets measured at smaller facilities.

Scattering Cross Sections of Impedance-Matched Bodies

Electromagnetic scattering from bodies with the surface impedance equal to the wave impedance of the surrounding medium shows a number of extremal features, including vanishing axial backscattering cross section in the case of bodies of revolution. This paper examines various scattering cross sections (mono- and bistatic, total scattering, absorption, and extinction) of electrically large arbitrarily shaped impedance-matched bodies, and it is shown that the backscattering cross section of arbitrarily shaped convex impedance-matched bodies vanishes in the optical limit. Furthermore, it is conjectured that considered as functions of the surface impedance, the mean total scattering cross section has a global minimum and the mean absorption cross section a global maximum when the body is illuminated by plane waves with random incidence direction and polarization.

Imaging by a double negative metamaterial slab excited with an arbitrarily oriented dipole

The imaging capability of nonideal double negative metamaterial slabs excited by arbitrarily oriented electric or magnetic dipoles is investigated. A dipole oriented parallel to the interface of the slab excites transverse electric and transverse magnetic modes simultaneously, which are transmitted unequally by the slab if either the slabs relative permittivity (er) or permeability (μr) or both are perturbed from the ideal case, i.e., er=μr=−1 for a slab in vacuum. Approximations in the electrostatic limit, valid for modes with large wave numbers, fail to predict this phenomenon, and more accurate analysis of the field distribution in the vicinity of the image plane behind a nonideal slab becomes important. By expressing the fields in terms of a one‒dimensional Hankel transform in the spectral domain and using an adaptive Gauss‒Kronrod quadrature, a tool for evaluating the spatial field intensity in the vicinity of the image plane behind the slab is developed. The calculated field intensities reveal that a double negative slab does not focus in the three‒dimensional space and is only capable of two‒dimensional imaging.

An improved image-based near-field-to-far-field transformation for cylindrical scanning surfaces

An improved image-based circular near-field-to-far-field transformation (NFFFT) developed recently by the authors for smaller measurement facilities and for targets with pronounced scattering centers offset from the center of the imaging area is extended to a cylindrical scanning surface. Scanning over a surface instead of a circle permits RCS estimations for targets whose size in the direction perpendicular to the measurement plane is comparable to their extension in the measurement plane. The approach consists in near-field imaging of the target, followed by integration of the image. The focusing operator, which is used to generate the image, is built in such a way so that the image of an electrically small PEC sphere is exactly the delta function. The paper describes the effect of various transformation parameters such the sampling rates in the input data and in the image domain on the quality of RCS estimations.