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Introduction. Computer-aided design systems for microwave devices are an effective tool for assessing the backscattering characteristics of complex-shaped objects. However, these calculations are often associated with significant computational costs, especially at large values of the ratio of the characteristic dimensions of the object to the wavelength. The use of asymptotic methods in combination with the mesh coarsening of object partition can significantly reduce these costs. However, in each practical case, this leads to a deterioration in the accuracy of the estimates obtained, which is hard to predict.Aim. Comparative assessment of the results of modeling the scattering field in the CAD of microwave devices using various methods for calculating and detailing the object model in the decimeter and centimeter wavelength ranges.Materials and methods. The research object was an anti-tank guided missile FGM-148 Javelin. The scattering field of Altair FEKO microwave devices was modeled in CAD using the methods of moments and physical optics in the frequency range from 1 to 10 GHz and angles from 0 to 180°. A comparison of one-dimensional backscatter diagrams and radar images obtained using these methods was carried out.Results. For the class of objects under consideration, the method of physical optics provides acceptable accuracy at frequencies of 5 GHz and higher with a step of partitioning the model surface of the order of one centimeter and a total calculation duration of the order of several minutes (Intel Core i5-4460 PC / 3.2 GHz / 8 MB RAM). At lower frequencies, acceptable accuracy and a similar calculation duration are achieved when calculating by the method of moments and a partitioning step of about 20 cm. The possibility of using the Altair FEKO CAD system for modeling radar images of objects with a resolution of at least 20 cm is demonstrated.Conclusion. The results obtained complement the well-known studies in the field of comparative assessment of the time and accuracy characteristics of various methods for calculating the scattering field of objects in the CAD of microwave devices.

The paper considers one of the numerical methods to solve problems of scattering electromagnetic waves on the systems formed by parallel-oriented cylindrical elements – two-dimensional photonic crystals. The method is based on the classical partition approach used for solving the wave equation. Тhe method principle is to represent the field as the sum of the primary field and the unknown secondary field scattered on the medium elements. The mathematical expression for the latter is written as the infinite series according to elementary wave functions with unknown coefficients. In particular, the N elements-scattered field is found as the sum of N diffraction series in which one of the series is composed of the wave functions of one body and the wave functions in the remaining series are expressed in terms of the eigenfunctions of the first body using addition theorems. Further, to meet the boundary conditions, on the surface of each element, we obtain systems of linear algebraic equations with the infinite number of unknowns – the required expansion coefficients, which are solved by standard methods. A feature of the method is the use of analytical expressions to describe diffraction on a single element of the system. In contrast to most numerical methods, this approach allows one to obtain information on the amplitude-phase or spectral characteristics of the field only at the local points of the structure. The high efficiency of this method stems from the fact that there is no need to determine the field parameters in the entire area of space occupied by the multi-element system under consideration. The paper compares the calculated results of the transmission spectra of two-dimensional photonic crystals using the considered method with the experimental data and numerical results, obtained by other approaches, and demonstrates their good agreement.

ispartof: PHYSICAL REVIEW C vol:102 issue:6 status: published

The reflected field calculation from the object can be described with the set of point reflectors with the coordinates in electromagnetic wave plane of incidence corresponding to two-dimensional grid nodes with rather small-sized step. At the same time, the single scattering model which does not consider the re-reflection and point elements cross impact is used in the reflected field calculations. The rapid direct and inverse transformation algorithm is used. The numerical solution algorithms of the direct and inverse scattering problems on the object are offered. The method uses the ray representations scattering fields which are based on the Huygens-Fresnel principle. The graphic diagram of the reciprocal object positioning and the observation plane from the reflected electromagnetic field object is represented. The double reflecting Gaussian surface is graphically figured. The figures of the module and the complex amplitude electric field strength of the reflected wave from a double Gaussian surface argument are provided. To shape the surface of the unknown object the recovery shape algorithm is used, by means of reflected wave phase. This algorithm is based on finding the complex matrix elements in dependence on absolute phase, which is proportional to the appropriate point object distance.

The paper considers the problem of finding the power flux density of signals reflected from two objects with different symmetric scattering matrices when they are irradiated with a completely polarized wave. The authors consider the case when the eigenvalues of the matrix are different given the form of the unitary diagonalization of the matrix for this case. The relation defining the diagonal elements of the factor is given. A comparison is made between the power flux density of the signals reflected from two objects with different scattering matrices when they are irradiated with a completely polarized wave. The power flux density of the electromagnetic wave reflected by this object is determined mathematically. Based on the definition of the scattering matrix, a transition to incident waves is performed. A parameter characterizing the degree of polarization anisotropy of the fluctuating object is given. The ratio for radar contrast is given. It is concluded that if the vector of the incident electromagnetic wave differs only in the scalar multiplier from the eigenvector of the matrix, the radar contrast will reach its maximum value. When the vector of the incident wave is proportional to the eigenvector, the value of the radar contrast reaches its minimum value. A problem is considered when the scattering matrices of two objects are simultaneously reduced to a diagonal form by means of a congruence transformation. Conditions are determined under which the Graves matrix of two scattering objects is reduced to diagonal form by means of a congruent transformation. A necessary and sufficient condition for the existence of a polarization basis is obtained in which the scattering matrices of two objects will simultaneously have a diagonal form.

The reliability of non-linear junction detectors (NLJD) at detection of radio-electronic devices (RD) and scatterers of corrosion origin of the type “metal-oxide-metal” (MOM-structures) is investigayed. It is revealed that the presence of MOM-structures in the study space substantially impair the reliability of NLJD at revealing RD with the “small” non-linear effective area of dispersion (NEAD) of the probing signal. In this case determination of threshold levels of multiple harmonics and their ratios will not improve the efficiency of the NLJD use, which is associated with the peculiarities of MOM-structures current-voltage characteristics (CVC). The contacts between the metals Al, Cr, Ni have CVC with asymmetry, which are determined by the thickness and area of the oxide. The asymmetry can be of two types – positive and negative, have a clear and quasi-clear manifestation. It is shown that the choice of the optimal threshold ratio ensures the reliability of NLJD only upon detection of MOM-structures with quasi-clear CVC asymmetries of two types. In the case of MOM-structures with a clear CVC asymmetry of two types, the efficiency of the use of NLJD initially requires a significant decrease of levels of spurious emissions of the transmitting antenna., Исследована надежность детекторов нелинейных переходов (NLJD − Non Linear Junction Detector) при обнаружении радиоэлектронных устройств (РЭУ) и рассеивателей коррозионного происхождения типа “металл-окисел-металл” (МОМ-структур). Выявлено, что наличие в исследуемом пространстве МОМ-структур существенно ухудшает надежность NLJD при выявлении РЭУ с “малой” нелинейной эффективной площадью рассеивания (НЭПР) зондирующего сигнала. При этом задание пороговых уровней кратных гармоник и их соотношений не улучшит эффективность использования NLJD, что связано с особенностями вольт-амперных характеристик (ВАХ) МОМ-структур. Контакты между металлами Al, Cr, Ni имеют ВАХ с асимметрией, определяемые толщиной и площадью окисла. Асимметрия может быть двух типов  положительной и отрицательной, иметь явное и квазиявное проявление. Показано, что выбор оптимального порогового соотношения гарантирует надежность NLJD лишь при обнаружении МОМ-структур с квазиявными асимметриями ВАХ двух типов. В случае МОМ-структур с явной асимметрией ВАХ двух типов, обеспечение должной эффективности использования NLJD изначально требует существенного снижения уровней побочных излучений передающей антенны., Досліджена надійність детекторів нелінійних переходів (NLJD − Non Linear Junction Detector) при виявленні радіоелектронних пристроїв (РЕП) і розсіювачів корозійного походження типу “метал-окисел-метал” (МОМ-структур). Виявлено, що наявність в досліджуваному просторі МОМ-структур істотно погіршує надійність NLJD при виявленні РЕП з “малою” нелінійною ефективною площею розсіювання (НЕПР) зондуючого сигналу. При цьому завдання порогових рівнів кратних гармонік і їх співвідношень не поліпшить ефективність використання NLJD, що пов'язано з особливостями вольт-амперних характеристик (ВАХ) МОМ-структур. Контакти між металами Al, Cr, Ni мають ВАХ з асиметрією, що визначаються товщиною та площею окислу. Асиметрія може бути двох типів − позитивною і негативною, мати явний і квазіявний прояв. Показано, що вибір оптимального порогового співвідношення гарантує надійність NLJD лише при виявленні МОМ-структур з квазіявними асиметріями ВАХ двох типів. В разі МОМ-структур з явною асиметрією ВАХ двох типів, забезпечення належної ефективності використання NLJD спочатку вимагає істотного зниження рівнів побічних випромінювань передавальної антени.

We demonstrate that optical Fano resonance can be induced by the anisotropy of a cylinder rather than frequency selection under the resonant condition. A tiny perturbation in anisotropy can result in a giant switch in the principal optic axis near plasmon resonance. Such anisotropy-induced Fano resonance shows fast reversion between forward and backward scattering at the lowest-energy interference. The near and far fields of the particle change dramatically around Fano resonance. The topology of optical singular points and the trajectory of energy flux distinctly reveal the interaction between the incident wave and the localized surface plasmons, which also determine the far-field scattering pattern. The anisotropy-induced Fano resonance and its high sensitivity open new perspectives on light-matter interactions and promise potential applications in biological sensors, optical switches, and optomechanics.