Andrey O. Perov

Explicit Conditions for Virtual Boundaries in Initial Boundary Value Problems in the Theory of Wave Scattering

This paper deals with the problem of finding a correct way of restricting the computational domain in the FDTD-method in its application to the analysis of transient wave processes in infinite homogeneous regions containing compact inhomogeneities. The formulation of the explicit ABCs (Absorbing Boundary Conditions) in such a way that they do not distort the physical model simulated by the mathematics, and the incorporation of these ABCs in the computational scheme form the basis of the approach presented here. A number of numerical results are given, illustrating in particular the performance of the exact ABCs in comparison with lower order approximations.

Abnormal propagation of EMW through below cutoff holes and intrinsic oscillations of waveguide objects and periodic structures

Spectral theory is used to explain the effect of propagation through below cutoff holes. Intrinsic oscillations of the corresponding waveguide and periodic open resonators are studied. Their influence on the frequency characteristic is demonstrated for various structures: from waveguide to array.

Natural oscillations providing 90° polarization plane rotation by planar chiral double-slot irises

The common origin of the “enhanced transmission” through small holes and polarization plane rotation (“optical activity”) resonances peculiar for a pair of conjugated planar chiral irises is demonstrated. The eigenoscillation spectra are studied extensively from the “aperture” eigenoscillations of plane junctions responsible for the “enhanced transmission” through the planar chiral iris up to the eigenoscillations of “dihedral” symmetry formed in a composite double slot planar chiral iris. Their excitation results in polarization plane rotation of the dominant mode in a square waveguide. A new compact unit for TE01 to TE10 conversion operating within 5–10% frequency band is proposed and validated experimentally. All conclusions are valid for various types of metasurfaces based on the “fish-net” gratings.

Model Problems of Pulse Sensing

The radio-locating means for determination of layered media parameters and visualization of objects or voids hidden in them have gained wide-spread acceptance in various fields, namely, civil engineering, geodesy, use of hydraulic-engineering structures and of oil-pipe-lines, etc. The solution of the engineering problems arising therewith requires the development of essentially new approaches. Traditional theoretical and experimental methods have made possible only the first generation of radars with both small signal penetration depth and incomplete retrieval of useful information from remote sensing data. Quite reasonable hopes for improvement of the situation are widely associated with the construction of radars based on nonsinusoidal waves. A central theoretical problem here consists in correct interpretation of the results of measurements, demanding for its solution adequate mathematical models (and algorithms) describing the transient processes in the part of space under research. Model problems of pulse sensing are initial boundary value ones in unbounded regions with inhomogeneous compact objects. The key to the effective solution of them lies with a proper truncation of the computational domain in finite-difference methods, i.e. in a limitation of such kind that, on the one hand, reduces the essentially open problem to the closed one, and, on the other hand, does not effect on accuracy and reliability of the data obtained. Our paper is just devoted to the analysis of this problem. In the first section, the problem of scattering of nonsinusoidal waves by a perfectly conducting compact object imbedded in an inhomogeneous half-space with an irregular boundary is considered. The second section is devoted to the extension of the results to other situations peculiar for pulse sensing: an inhomogeneous compact object and a stratified dielectric structure in a field of nonsinusoidal waves and a pattern-forming structure. All model problems are two-

Recent advances in computational electromagnetics for microwaves in IRE NASU

Recent advances in problem-oriented and general-purpose microwave-oriented software and applications developed in the department of computational electromagnetics are considered. Numerical-analytical automatic mode-matching based models are extended on the objects given in cylindrical coordinate system. The geometry has to be specified as the set of piece-wise coordinate fragments in Cartesian (MWD1 or MWD2 with account of edge behavior) or in Cartesian or cylindrical coordinates (MWD3) with automatic cross-section geometry recognition and subsequent formation of corresponding mode-matching technique and S-matrix based numerical algorithms. The future extension to the double-periodical screens and multilayer printed circuits (MWD4) is described moving to terahertz frequency band and “metamaterial” investigations. A set of new microwave devices is proposed which are based on the nonstandard physical principles such as the fringing field interaction, new types of eigen-oscillations of 3D open objects and artificial “optical activity”. They are the band-stop and band-pass waveguide filters, antenna-feed units, polarization rotators, twists etc.

Eigenmodes and polarization rotation in the conjugate stacked structures

The system of conjugated stucked screens with rotational symmetry is considered to rotate polarization of the insident plane wave. It is discussed connection between the symmetry of the structure and its polarization response. The new dihedral eigenmodes, which are origin of the such resonant behaviour are investigated and illustreted by numerical results.

On the nature and general regularities of optical activity in planar-chiral double-layer metamaterials

The most interesting examples of various double-layer metamaterials that provide “optical activity” are presented to reveal the motivation of use of different cell topologies. The phenomena of the giant “optical activity”, existence or lack of perfect matching, multi-band phenomena, the role of higher space harmonics, and influence of space spectrum rarefying are considered and explained based on the spectral theory of opened structures.

Polarization Plane Rotation by Arbitrary Angle Using

A compact waveguide polarization rotator, able to turn the polarization plane by an arbitrary angle, is proposed. Its operational principle is based on a strong electromagnetic coupling between two conjugated quadruple-slot planar-chiral irises in a square waveguide by the below cutoff modes. The physical interpretation for the observed phenomenon is provided based on the analysis of the eigenoscillations of such a D4 symmetrical object considered as an open waveguide resonator. It is demonstrated that there exist two perfect matching points controlled by the iris geometry and width of the narrow gap between two planar chiral components. The reported unit has a bandwidth of several percent with return loss better than 20-30 dB. The conclusions of this work are fully applicable to double-periodical two-layer screens or metasurfaces having such square cells.

{ D}_{4}

An exact full-wave model for a design of multi band horns based on the hybrid mode matching and Winner-Hopf method is described. The model is well suited for optimization owing to the mode-matching approach. The complex horn structure is constructed from a set of fundamental building blocks, and the scattering matrix of the entire device is found by cascading of the scattering matrices of the individual components. The main steps of the realization for a three-band (S/X/Ka) feed horn compatible with VLBI2010 standards are considered.

Symmetrical Structures

A possibility to design a compact polarization rotator based on the structures of dihedral symmetry is studied. Here, the diaphragms with several equal rectangular apertures are considered as dihedral symmetry structures. Ultimate performances of the rotators considered are obtained by using different optimization procedures. They demonstrate acceptable reflection in the predetermined frequency band The rotators that achieve the polarization plane rotation by an angle of choice are examined as well.