Tatjana Asenov

Sampling of stochastic electromagnetic fields

Stochastic electromagnetic fields can be described by the auto- and cross correlation spectra of the electric and magnetic field values at pairs of points in space. In this work the characterization of noisy electromagnetic fields by sampling the field values in pairs of sampling points is discussed. Sampling of the electric or magnetic field values in all pairs of a set of sampling points yields the correlation matrix of the field samples. If the near-field in a surface of reference enclosing the stochastic field sources is sampled and characterized by its correlation matrix the field radiated in the space outside the surface of reference can be calculated and described by the field correlation spectra. Depending on the number of statistically independent field sources the eigenvalue decomposition of the correlation matrix yields a compact description of the measured EM noise field.

Efficient DOA estimation of impinging stochastic EM signal using neural networks

In this paper a method for the accurate and fast determination of direction of arrival (DOA) of impinging electromagnetic signal radiated from stochastic sources in the far-field is proposed. The method is based on neural models using MLP (Multi-Layer Perceptron) artificial neural network. To illustrate the applicability of the proposed method, two MLP models for one-dimensional (1D) DOA estimation (in azimuth plane) are presented: MLP model for the estimation of angle position of one stochastic source and MLP model for the estimation of two stochastic sources position at fixed angle distance. Presented models perform very fast 1D DOA estimation and therefore they are very suitable for the real time applications. The architecture of developed models, their training results and simulation results are described. in details.

Exact analytical solution for fields in gradient index metamaterials with different loss factors in negative and positive refractive index segments

Abstract. Gradient refractive index metamaterials are of interest for various applications of transformation optics. Wave propagation through gradient index metamaterials using an exact analytical approach is investigated. Composite materials containing constituents with negative real and positive real indexes of refraction are considered. An exact analytical solution for the field distribution is obtained for the sinusoidal spatial variation of complex effective permittivity and permeability along a fixed direction, under the assumption that the wave impedance remains spatially uniform across the structure. Loss factors in the constituent materials can be different from each other corresponding to the realistic situations. Temporal dispersion can be arbitrary subject to the physical limitations imposed by the Kramers-Kronig relations. A numerical model based on the Z-transform is developed to verify the analytical results. The approach can be applied to arbitrary periodic refractive index profiles using the Fourier series method.

Efficient characterization of stochastic electromagnetic fields using eigenvalue decomposition and principal component analysis methods

Stochastic electromagnetic fields can be described by the correlation function of the field amplitudes in all pairs of space points. We show that the description of stochastic electromagnetic fields by correlation matrices can be simplified using the principal component analysis (PCA) for eigenvalue decomposition. In this paper, the principal component analysis and the eigenvalue decomposition approach are applied for decomposing and reducing the correlation matrix describing the correlations of the sampled field amplitudes. Subsequently conventional eigenvalue decomposition and the PCA approaches are compared.

Extended foster approach for equivalent circuit synthesis of lossy microwave circuits

In this paper, a circuit synthesis approach based on an extended Foster canonical expansion for representation of distributed passive lossy electromagnetic structures is described. Compact lumped element model is extracted from data provided by numerical TLM method in the time-domain and then embedded into a conventional circuit simulator. The equivalent circuit synthesis procedure is applied to the two-port low-pass and band-pass microstrip filters. The resultant circuits with elements are analyzed and the obtained S parameters results are in a good agreement with numerical results.

Time-domain modelling of graded refractive index metamaterials by using 3D TLM Z-transform method

In this paper, a numerical three-dimensional (3D) model of electromagnetic left-handed metamaterials (LH MTM) is used to describe composite right-left handed (RLH) structures with graded refractive index profile commonly named GRIN MTM. The model is developed by using the Transmission Line Matrix (TLM) Z-transform method and Drude model to account for dispersive LH MTM properties in the time-domain. GRIN slabs with abrupt, hyperbolic tangent, cosine, linear, and exponential refractive index profiles have been considered. The accuracy, efficiency and stability of the proposed approach for GRIN MTM modelling are verified by using analytical solutions.

Lossy transmision with arbitrary gradient permittivity and permeability and constant impedance throughout the structure

We present a remarkably simple exact analytical solution for the electromagnetic field distribution across an infinite metamaterial composite with an arbitrary graded variation of complex effective permittivity and permeability for the case of constant impedance across the structure. Arbitrary temporal dispersion and losses are allowed and the model is generally applicable to different inhomogeneous and anisotropic media simultaneously containing positive and negative refractive index constituents, as long as the effective medium approximation remains valid. The analytical solution is validated by a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms, where a close agreement between the analytic and numerical results is obtained.

Lossy microwave circuits — Systematic synthesis of equivalent lumped element model based on extended Foster canonical expansion

An application of systematic network model synthesis approach for representation of distributed passive lossy microwave circuits is investigated in the paper. This approach is based on a Foster canonical expansion for lossless circuits and its modification to account for losses. Equivalent compact lumped element model is extracted from the data provided by numerical TLM method in the time-domain and then embedded into a conventional circuit simulator. The synthesis procedure is applied to a lossy band-pass microstrip filter and a lossy coupled line coupler. Impact of dielectric losses of a substrate is also highlighted with the respect of the presented approach applicability.