Nebojsa Doncov

1D and 2D economical FIR filters generated by Chebyshev polynomials of the first kind

Christoffel–Darboux formula for Chebyshev continual orthogonal polynomials of the first kind is proposed to find a mathematical solution of approximation problem of a one-dimensional (1D) filter function in the z domain. Such an approach allows for the generation of a linear phase selective 1D low-pass digital finite impulse response (FIR) filter function in compact explicit form by using an analytical method. A new difference equation and structure of corresponding linear phase 1D low-pass digital FIR filter are given here. As an example, one extremely economic 1D FIR filter (with four adders and without multipliers) is designed by the proposed technique and its characteristics are presented. Global Christoffel–Darboux formula for orthonormal Chebyshev polynomials of the first kind and for two independent variables for generating linear phase symmetric two-dimensional (2D) FIR digital filter functions in a compact explicit representative form, by using an analytical method, is proposed in this paper. The formula can be most directly applied for mathematically solving the approximation problem of a filter function of even and odd order. Examples of a new class of extremely economic linear phase symmetric selective 2D FIR digital filters obtained by the proposed approximation technique are presented.

TLM modeling of the circular cylindrical cavity loaded by lossy dielectric sample of various geometric shapes.

The modeling of the cylindrical metallic cavity with circular cross-section loaded by lassy dielectric sample of various geometric shapes is done by using the Transmission-Line Matrix (TLIVP method. For modeling purposes, a hybrid symmetrical condensed node (HSCN) in cylindrical coordinates, developed and implemented in the appropriate software, is applied. The proposed TLM models for several characteristic geometric shapes of the lassy dielectric sample are described in detail, the modeling process is discussed and the influence of the load form on the resonant frequencies of the cavity is investigated In addition, the applied TL 11 approach is experimentally verifiedfor two cases of cavity load form.

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.

Lossy gradient index transmission optics with arbitrary periodic permittivity and permeability and constant impedance throughout the structure

A remarkably simple exact analytical solution is obtained for the electromagnetic field distribution across infinite metamaterial-containing composites with any arbitrary periodic 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.

Hybrid Empirical-Neural Model of Loaded Microwave Cylindrical Cavity

A hybrid empirical-neural (HEN) model, to account for a loading effect of arbitrary raised dielectric slab in a microwave cylindrical metallic cavity, is presented. It is based on combination of an approximate model, as a rough empirical knowledge holder, and multi-layer perceptrons (MLP) neural network. In comparison with the model based only on MLP network, more accurate and efficient resonant frequencies calculation is achieved.

Neural networks-based DOA estimation of multiple stochastic narrow-band EM sources

Localization of multiple stochastic narrow-band electromagnetic sources in the far-field is considered in the paper. Artificial neural networks-based approach is proposed to allow for an efficient direction of arrival (DOA) determination of electromagnetic signals radiated from stochastic sources as one of the key steps in the source localization procedure. It uses correlation matrix, obtained by signal sampling via antenna array in far-field scan area, to train an appropriate model based on MLP (Multi-Layer Perceptron) neural network. Proposed approach is validated on the example of a neural model performing accurate and fast one-dimensional (1D) DOA estimation of the position of three stochastic sources placed at fixed angle distance in azimuth plane.

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.

Neural Network Approach for Efficient DOA Determination of Multiple Stochastic EM Sources in Far-field

An efficient approach for determination of incoming direction of electromagnetic (EM) signals radiated from multiple stochastic sources in far-field is presented in this paper. The approach is based on using a neural model realized by the Multi-Layer Perceptron (MLP) artificial neural network. MLP neural model, successfully trained by using correlation matrix of signals sampled by receiving antenna array, can be used to accurately determine a direction of arrival (DOA) of radiated EM signals and afterward a location of each of multiple stochastic sources in azimuth plane. Presented model is suitable for real-time applications as it performs fast the DOA estimation. The model architecture, results of its training and testing as well as simulation results are described in details in the paper.

A combined wave digital/full-wave electromagnetic approach used for response calculation in equivalent networks of microwave circuits

In this paper, a combined wave digital/full wave electromagnetic (EM) approach is used to synthesize wave digital networks of microstrip structures with step and capacitive gap discontinuities. The wave digital approach is applied to model uniform transmission lines in these structures, while the full-wave EM tool provides a generalized S-parameter description of discontinuities, used to generate their approximate equivalent network models. In the case of capacitive gap discontinuity in the end-coupled structures, the synthesis procedure is based on equivalent circuit representation by using admittance (J-) inverters and half-wavelength resonators. Wave digital model of J-inverter is formed by use of a two-port parallel adaptor. The combined technique is used for efficient modeling and analyzing of two different types of microstrip band-pass filters.

Shielding Effectiveness Estimation by using Monopole-receiving Antenna and Comparison with Dipole Antenna

Abstract In this paper, a numerical analysis of shielding properties of a protective metal enclosure has been performed by simulating a receiving antenna placed inside. Here, the main focus is put on the monopole antenna type. This antenna type is used in an experimental set-up to measure the shielding effectiveness (SE) of the enclosure as often as some other antennas such as dipole. Numerical model, based on the Transmission-Line Matrix (TLM) method, is applied to numerically investigate an impact this antenna might have on a detected level of electromagnetic (EM) field when it is used in the SE measurements. As in experiments, the estimation of SE of an enclosure in the numerical model is performed based on the current induced on the antenna, directly provided by a compact TLM wire model. The model accuracy is verified through a comparison with the experimental results from the literature. The analysis includes the monopole antenna with different radii and lengths, in order to consider changes in the resonant frequencies and the SE level of enclosure. Finally, the enclosure with either the monopole or the dipole is simulated in order to compare their influence on EM field distribution inside the enclosure.