Nebojsa Doncov

University of Niš | NIS · Faculty of Electronic Engineering

Artificial neural networks‐based module for fast direction‐of‐arrival (DoA) estimation of the signal received by multi‐element textile wearable antenna array (TWAA) is proposed in this paper. The developed multilayer perceptron (MLP) DoA module considers the effects of changing the gain of the antenna elements, the distance between the antenna elem...

The impact of deformations on wearable antenna performance has been analyzed both experimentally and computationally. However, the reported results have been inconsistent and often contradictory. This paper highlights how the choice of computational mesh, namely cubic and curvilinear cylindrical mesh, that are applied to the problem of cylindricall...

This paper presents the suitability and computational features of the cylindrical TLM approach, when it is used as an accurate and efficient alternative for the analysis of the bending effect on performances of the antenna operating in an on-body mode. A design goal was to create the model of the rectangular patch antenna wrapped around the part of...

In this paper, the impact of an electromagnetic absorber inside a protective metal enclosure is analyzed. The absorber is put inside the enclosure in order to improve its shielding effectiveness, especially at the first resonant frequency. Different absorber's sheet positions inside the enclosure are analyzed. The absorber sheet dimensions are fitt...

MLP_DoA module, being an integral part of the smart TWAA DoA subsystem, intended for fast DoA estimation is proposed. Multilayer perceptron network is used to create the MLP_DoA module that provides a radio gateway location in azimuthal plane at its output when a spatial correlation matrix, found by receiving the radio gateway signal using two-elem...

We present general approach for antenna design and optimization based on consensus of results from a number of independently trained deep neural networks. The aim of using the consensus is to reduce the uncertainty of results from a single deep neural network. The approach leads to several orders of magnitude faster antenna optimization and design...

Accurate near-field measurements for either deterministic or stochastic electromagnetic fields characterization require a relevant process that removes the influence of the probes, transmission lines, and measurement circuits. The main part of the experimental work presented here is related to a calibration procedure of a test setup consisting of a...

Z-TLM based compact modeling approach for dispersive media exhibiting magnetoelectric coupling is presented in this paper. Scattering parameters based representation of considered medium is created in a form of compact model by extracting effective electromagnetic parameters using a retrieval method, and implementing them into a non-uniform TLM gri...

Hierarchical neural model for an efficient one‐dimensional direction of arrival (DoA) estimation of stochastic electromagnetic (EM) sources with a variable radiation power is proposed. Model is trained to provide an azimuth position of such sources based on a spatial correlation matrix obtained by a signal sampling at a reception point and then use...

Numerical computational methods on a Cartesian grid and analytical approaches face many problems and limitations when modeling antenna structures of circular/cylindrical geometry is concerned. This paper presents possibilities and computational demands of the cylindrical TLM approach with a wire modeling ability, implemented through in-house develo...

This paper introduces a design of a frequency adjustable dual-band circular patch antenna with a gap-ring-slot accompanied by a study of a cylindrical TLM method effectiveness and capabilities. The antenna is fabricated on Rogers 4003 substrate and measured results have been used to validate the used approach. Through comparison with corresponding...

In order to provide a constant and complete operational picture of the maritime situation in the Exclusive Economic Zone (EEZ) at over the horizon (OTH) distances, a network of high frequency surface-wave-radars (HFSWR) slowly becomes a necessity. Since each HFSWR in the network tracks all the targets it detects independently of other radars in the...

With maximum range of about 200 nautical miles (approx. 370 km) High Frequency Surface Wave Radars (HFSWR) provide unique capability for vessel detection far beyond the horizon without utilization of any moving platforms. Such uniqueness requires design principles unlike those usually used in microwave radar. In this paper the key concepts of HFSWR...

Compact modeling approach of anisotropic media by using the Z-TLM method is proposed. Thin anisotropic multilayer material is efficiently described through connection procedure between two Z-TLM mesh cells, by using the scattering parameters to create a digital filter-based compact model. Model is incorporated into non-uniform TLM grid given here i...

Neural model capable to accurately and efficiently predict a propagation delay of electromagnetic signal in the ionosphere is proposed in this paper. The model performs this prediction for a given geographic location in Europe between 40?(N) and 70?(N) latitude and 10?(W) and 30?(E) longitude, according to the following parameters: particular day i...

MultiLayer perceptron (MLP)-based neural model for an efficient 1D DoA estimation of highly correlated stochastic EM sources is proposed. Model extracts this information from a spatial correlation matrix obtained by sampling stochastic signals by a receiving antenna array. Algorithm for optimal selection of correlation matrix elements from the uppe...

In this work, a novel design of patch antenna with two symmetrical slits and two closely spaced resonances is proposed. Novel patch antenna demonstrates a great flexibility in impedances adjustment at both resonances that is of a great importance in the design of series fed antenna arrays with a large number of radiating elements. Printed antenna w...

This letter addresses the ability of the TLM method with an incorporated compact wire model, both adjusted to the cylindrical grid, to accurately model a coaxially fed patch-ring antenna together with an investigation of the computational efficiency in a modeling procedure. Design of the antenna has included an optimization of the coaxial feed loca...

This paper analyzes the impact of an incident plane wave direction on the shielding effectiveness of a metal enclosure with hexagonal or square air-vents. The analysis is conducted based on the compact TLM air-vent model for hexagonal and square perforations, for small azimuth and elevation angles of the incident plane wave. It is shown that even a...

Global Christoffel–Darboux formula for different polynomials has already been used for the filter design. Here, this formula for orthonormal Chebyshev polynomials of the second kind and for two independent variables is applied in generating novel class linear-phase two-dimensional (2-D) finite impulse response (FIR) digital filter functions. In thi...

One-dimensional (1D) Transmission Line Matrix (TLM) method with Z-transforms, is applied in the paper to allow for an efficient time-domain simulation of thin anisotropic conductive panel of dispersive behavior. It uses a digital filter model to incorporate the scattering coefficients of the panel at two TLM cells interface in order to avoid a fine...

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 ot...

Wave digital filters (WDFs) represent a class of digital filters with a particular interest. WDFs were developed initially by Alfred Fettweis in the early 1970s for digitizing lumped electrical circuits composed of inductors, capacitors, resistors, and other elements of classical network theory. Full-wave electromagnetic (EM) modeling techniques a...

In this paper, the shielding properties related to a protective metal enclosure with airflow aperture arrays are numerically analyzed. As a numerical model, a TLM method, either in a conventional form based on fine mesh to describe apertures presence or enhanced with the compact air-vent model is employed. The main focus in the paper is on examinin...

Stochastic electromagnetic fields can be described by correlation spectra. In this paper, we describe modeling of the aperture field for a cavity with multiple stochastic sources for field excitation within the cavity with an arbitrary degree of correlation between the sources. In this modeling approach, the contribution to the aperture field from...

An efficient neural network-based approach for tracking of variable number of moving electromagnetic (EM) sources in far-field is proposed in the paper. Electromagnetic sources considered here are of stochastic radiation nature, mutually uncorrelated, and at arbitrary angular distance. The neural network model is based on combination of probabilist...

In this paper, a numerical analysis of the shielding properties related to a protective metal enclosure with ventilation apertures is performed. As a numerical tool, the TLM method, either in conventional form based on fine mesh to describe apertures presence or enhanced with the compact air-vent model is used. The main focus in the paper is on exa...

This paper investigates possibilities and advantages of the integral cylindrical TLM method when the subject of modelling is a coax-fed circular patch antenna with a shorting pin and an annular ring. To point out advantages of the cylindrical TLM mesh, obtained results representing S11 parameter and input impedance of the modelled antenna are compa...

In this paper, a neural model intended to efficiently determine the number of moving electromagnetic sources of stochastic radiation in the monitoring space sector is presented. Neural model is based on a probabilistic neural network. As an illustration, one-dimensional case is considered in which the noisy sources are moving only in the azimuth pl...

The paper investigates the feeding structures for printed antenna arrays with parallel reflector and their influences on antenna parameters. Two printed antenna arrays are presented. The first consists of ten series fed symmetrical dipoles with tapered impedances. The second is the array of eight symmetrical dipoles that are fed by a tapered distri...

A mixed modeling technique combining an electromagnetic (EM) modeling with a wave digital approach is employed here to get the scattering parameters of microstrip chamfered bend structures. This paper provides a two-port equivalent wave digital network model of microstrip right-angled bend configuration. The effects of discontinuity are more accura...

In this paper,a digital filtertechnique is used for an efficient modelling of thin anisotropic conductive materials.Appropriate digital filter is developed to incorporate the scattering parameters of an anisotropic conductive panel allowingto includeits presencewithout the need to model the panelthickness. The filter is implemented in the Z-TLM met...

An original analytical method, based on modified Christoffel–Darboux formula, is used in the paper in order to synthesise a linear-phase band-pass finite impulse response (FIR) filter function that can have an effect of Hilbert transformer. New structure of the band-pass FIR filter in recursive realisation, together with the corresponding differenc...

The transmission-line matrix method enhanced with the compact wire model in a cylindrical grid is used for modelling of a coaxially loaded cylindrical cavity resonator with probes inserted into the cavity. Benefits of using a cylindrical grid instead of rectangular, related to precise modelling of cavity boundaries, a coaxially shaped dielectric sa...

An efficient direction of arrival (DOA) estimation of multiple electromagnetic sources by using artificial neural network (ANN) approach is presented in the paper. Electromagnetic sources considered here are of stochastic radiation nature, mutually uncorrelated and at arbitrary angular distance. The approach is based on training of the ANN in which...

This paper presents an artificial neural network (ANN)-based model for two-dimensional direction of arrival (DOA) estimation of two coherent sources. The proposed model is composed of two neural networks, one for each radiating source. Datasets for training and testing of the neural model are formed assuming narrowband signal model and a 4 × 4 rect...

Shielding effectiveness of a protective metal enclosure with apertures and receiving antenna placed inside is numerically considered. The purpose of the antenna, here considered as a dipole, is to detect the electromagnetic (EM) field level within the enclosure and to transfer this information via a coaxial cable to a network analyzer. This follows...

This article presents development and validation of an artificial neural network (ANN)-based model for accurate two-dimensional direction of arrival estimation of two coherent sources. The ANN model is developed using simulated signals and its performance is evaluated by measurements inside an anechoic chamber. Simulations and experiments show good...

3-D TLM approach based on the cylindrical grid and enhanced with the compact wire model has been used for modelling of an inverted circular microstrip patch (IMCP) antenna with the coaxial feed. The simulated results have been compared with the measured results and rectangular grid based TLM results. Additional, the influence of the air gap height...

This paper deals with an impact of receiving antenna placed in a metal enclosure on an electromagnetic field distribution within the enclosure, and thus on its shielding effectiveness. In an experimental setup, a frequently used tool for measuring the electromagnetic field level at certain points within the enclosure is a dipole antenna connected t...

In this paper, numerical model of metal enclosure with apertures and monitoring antenna is considered for the purpose of accurate shielding effectiveness calculation. TLM method incorporating wire node model is used to account for the presence of monitoring dipole or monopole antennas used in practice to detect the level of electromagnetic field at...

The application of the extremal property of Christoffel-Darboux formula for classical continual orthonormal polynomials to the theory of synthesis of continual filter functions and digital multiplierless linear phase One-Dimensional (1D) and Two-Dimensional (2D) FIR filter functions is completely studied and described by analytical methods, and the...

In this paper, a generalization of the wave digital models of admittance inverters is done, aiming to increase a number of types of microstrip structures that can be modeled bz using wave digital filter theory. Wave digital networks of admittance inverters (J, +90o ) and (J,-90o ), are described in details and developed here based on scattering par...

This paper explores applicability of the integral TLM method in a cylindrical grid for the purpose of modelling of coax-fed microstrip antennas in configurations of the circular patch antenna and cavity-backed inverted microstrip antenna. Obtained results representing S11 parameter are compared with corresponding results reached by the rectangular...

In this paper, MLP neural network-based approach is proposed for an efficient direction of arrival (DOA) estimation of multiple narrow-band electromagnetic sources of stochastic nature in far-field. Neural network is trained to perform the mapping from the space of signals described by correlation matrix, obtained by signal sampling in far-field sc...

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 f...

This paper outlines the concept of combined wave digital/full-wave electromagnetic (EM) approach and its use to synthesize wave digital network of microstrip structure with parallel-coupled line sections. The synthesis procedure is based on equivalent circuit representation by using admittance (J-) inverters and half-wavelength resonators. J-invert...

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 p...