Marija Nikolic | University of Belgrade (original) (raw)

Papers by Marija Nikolic

Abstract In this paper a novel design of a wideband antenna that can operate in two different, c... more Abstract In this paper a novel design of a wideband antenna that can operate in two different, complementary UWB sub-bands is presented. The proposed antenna is a dual layer design, consisting of a microstrip feed line with embedded PIN diodes on the back side of ...

We consider the problem of using electromagnetic sensing to estimate targets in complex environme... more We consider the problem of using electromagnetic sensing to estimate targets in complex environments, such as when they are hidden behind walls and other opaque objects. The often unknown electromagnetic interactions between the target and the surrounding area, make the problem challenging. To improve our results, we exploit information in the multipath of the objects surrounding both the target and the sensors. First, we estimate building layouts by using the jump-diffusion algorithm and employing prior knowledge about typical building layouts. We also take advantage of a detailed physical model that captures the scattering by the inner walls and efficiently utilizes the frequency bandwidth. We then localize targets hidden behind reinforced concrete walls. The sensing signals reflected from the targets are significantly distorted and attenuated by the embedded metal bars. Using the surface formulation of the method of moments, we model the response of the reinforced walls, and inco...

There are several sensitive spots in the WIPL analysis of the interdigital microwave filters. If ... more There are several sensitive spots in the WIPL analysis of the interdigital microwave filters. If it is not treated properly, the end effect causes significant errors in determination of their central frequencies. Coarse segmentation leads to underestimated coupling among transmission lines. Proper and careful modeling in WIPL can improve the overall accuracy of the numerical results. To that purpose, several metallic interdigital filters have been designed, machined, measured, and modeled by WIPL. The theoretical results were refined with the aim to match experimental data. Hence, guidelines are derived about the required accuracy of integration and approximation in WIPL, as well as subdivision of critical surfaces. The deducted rules can serve in the analysis of similar classes of coupled-line microwave filters, such as combline filters.

2010 IEEE Antennas and Propagation Society International Symposium, 2010

UWB antennas with embedded stubs or slots can create a notch in the frequency range. The frequenc... more UWB antennas with embedded stubs or slots can create a notch in the frequency range. The frequency notch and therefore the reduced radiation intensity is confined to frequencies used by other applications in order to achieve reduced interference. However the use of such resonant elements causes additional notches at the frequencies which equal to even or odd multiples of the

2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011

Abstract This paper discusses a microstrip fed UWB monopole antenna with a triple notch character... more Abstract This paper discusses a microstrip fed UWB monopole antenna with a triple notch characteristic. The three notches are designed to occur at the WiMAX frequency range, the WLAN and at a third frequency in the higher end of the UWB range. Each of the three ...

2007 2nd IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing, 2007

InSection 4,wedevelop thescalable approach were Estimating buildings layouts usingexterior radarl... more InSection 4,wedevelop thescalable approach were Estimating buildings layouts usingexterior radarlowresolution estimates areusedtoinitiate amorerefined measurements isa challenging taskinvolving the estimation. Finally, inSection 5,wepresent someresults of electromagnetic modeling, manyunknown parameters, and thesimulations limited numberofsensors. We propose using thejump- diffusion (1-4) algorithm asapowerful stochastic tool that 2.ELECTROMAGNETICMODELING canbeusedtodetermine thenumber ofwalls, estimate their unknown poiin an otepaaees.e mrv h Inourmodeling, weusea2Dmethodofmoments(MoM) unknownpsacode since electromagnetic modeling ofelectrically large convergence rateofthejump-diffusion algorithm by 3D structures ... 3Dstructures (such asbuildings) iSstill inadmissibly time developing aniterative procedure thatfirst finds low- consuming. However, theapproach we propose toestimate resolution estimates, whicharethenusedtoinitiate our theinterior ofthebuilding isgeneral andcanbeeasily moreaccurate estimation. Ourefficient usageofthe applied to3Dproblems. available frequency bandwidth, improves thecomputationalWe havedeveloped theMoM codebygeneralizing the speed thatotherwise wouldbehampered bytheforwardprogramfrom(5)toinclude arbitrarily shapedlossy- electromagnetic modeling.

2014 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2014

2010 48th Annual Allerton Conference on Communication, Control, and Computing (Allerton), 2010

We develop a near-field compressive sensing (CS) estimation scheme for localizing scattering obje... more We develop a near-field compressive sensing (CS) estimation scheme for localizing scattering objects in vacuum. The potential of CS for localizing sparse targets was demonstrated in previous work. We extend the standard far-field approach to near-field scenarios by employing the electric field integral equation to capture the mutual interference among targets. We show that the advanced modeling improves the capability to resolve closely spaced targets. We compare the performance of our algorithm with the performances of CS applied to point targets and beamforming. In this paper, we consider twodimensional (2D) scatterers. However, the results and conclusions can be extended to three-dimensional (3D) problems.

Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation, 2012

ABSTRACT We propose a two-step algorithm, for electromagnetic imaging of perfect electric conduct... more ABSTRACT We propose a two-step algorithm, for electromagnetic imaging of perfect electric conducting (PEC) targets hidden inside known medium, that uses l1 regularization. The basic assumption is that the target can be approximated by a few equivalent sources (filament currents). In the first step, for each incidence, we estimate the locations of the equivalent sources corresponding to the target scattering centers. However, false solutions may appear due to the multiple scattering or insufficient measurements. We eliminate the false solutions in the second step; we decide for each of the estimated equivalent sources weather it belongs to the target.

2012 IEEE 7th Sensor Array and Multichannel Signal Processing Workshop (SAM), 2012

2011 4th IEEE International Workshop on Computational Advances in Multi-Sensor Adaptive Processing (CAMSAP), 2011

ABSTRACT We consider electromagnetic imaging of targets hidden behind dielectric walls using spar... more ABSTRACT We consider electromagnetic imaging of targets hidden behind dielectric walls using sparse regularization. We assume that the targets can be suitably represented by a set of unknown filament currents as in the equivalent-source method. We combine the surface-equivalence theorem and the ray tracing to obtain a linear measurement model. We investigate the efficiency of the proposed method in reconstructing both dielectric and metallic targets.

2006 First European Conference on Antennas and Propagation, 2006

Page 1. COUPLING AMONG COLLOCATED LOOPS Marija M. Nikolić(1), Antonije R. Djordjević(1), Arye Neh... more Page 1. COUPLING AMONG COLLOCATED LOOPS Marija M. Nikolić(1), Antonije R. Djordjević(1), Arye Nehorai(2) (1)School of Electrical Engineering, University of Belgrade, PO Box 35-54, 11120 Belgrade, Serbia, Emails ...

2006 First European Conference on Antennas and Propagation, 2006

Page 1. IMPROVING RADIATION PATTERN OF MICROSTRIP ANTENNAS Marija M. Nikolić(1), Antonije R. Djor... more Page 1. IMPROVING RADIATION PATTERN OF MICROSTRIP ANTENNAS Marija M. Nikolić(1), Antonije R. Djordjević(1) ... The first aim of the present paper is to analytically evaluate the influence of the polarization currents using a simplified model of a patch antenna. ...

2011 19thTelecommunications Forum (TELFOR) Proceedings of Papers, 2011

Two-dimensional electromagnetic systems are, theoretically, infinitely long. Hence, they cannot b... more Two-dimensional electromagnetic systems are, theoretically, infinitely long. Hence, they cannot be realized in practice. The paper presents an experimental model of a two-dimensional electromagnetic system, which is based on the image theorem. Results of numerical simulations and measurements are compared, demonstrating excellent agreement.

2014 IEEE Conference on Antenna Measurements & Applications (CAMA), 2014

IEEE Transactions on Microwave Theory and Techniques, 2003

Gaussian-like filters are frequently used in digital signal transmission. Usually, these filters ... more Gaussian-like filters are frequently used in digital signal transmission. Usually, these filters are made of lumped inductors and capacitors. In the stopband, these filters exhibit a high reflection, which can create unwanted signal interference. To prevent that, a new low-reflection ladder network is introduced that consist of resistors, inductors, and capacitors. The network models fictitious transmission lines with Gaussian-like amplitude characteristics. Starting from the analysis of this network, a procedure is developed for synthesis of a new class of lumped-element RLC filters. These filters have transmission coefficients similar to the classical Bessel filters. In contrast to the Bessel filters, the new filters exhibit a low reflection both in the stopband and passband, they have a small span of element parameters, and they are easy for manufacturing and tuning.

IEEE Transactions on Geoscience and Remote Sensing, 2000

ABSTRACT We exploit the sparseness of induced currents on the surfaces of obscured perfectly cond... more ABSTRACT We exploit the sparseness of induced currents on the surfaces of obscured perfectly conducting (PEC) scatterers in developing a single-frequency imaging algorithm in 2-D space. We model the induced currents on the targets by a set of unknown filament currents to which we apply the surface-equivalence theorem. We use l1l_{1}l1 regularization to promote the solutions with a small number of equivalent sources placed in the vicinity of scatterer surfaces. The restored equivalent sources accurately determine the illuminated portions of the scatterer contours. We compare the performance of the algorithm with that of linear sampling (LSM) and MUSIC. We verify the proposed algorithm on the equivalent 3-D experimental model.

IEEE Transactions on Antennas and Propagation, 2000

Estimating building layouts using exterior radar measurements is a challenging task involving ele... more Estimating building layouts using exterior radar measurements is a challenging task involving electromagnetic modeling, many unknown parameters, and a limited number of sensors. We propose using the jump-diffusion algorithm as a powerful stochastic tool that can be used to estimate the number of walls, their unknown positions and other parameters. We develop an efficient iterative procedure that first uses low-frequency

IEEE Transactions on Antennas and Propagation, 2000

ABSTRACT We demonstrate that the utilization of the diffraction by antenna platforms increases th... more ABSTRACT We demonstrate that the utilization of the diffraction by antenna platforms increases the effective array aperture. We conduct the analysis on a realistic model of an airborne platform and use the Cramer-Rao bound to assess the level of improvement due to the presence of the platform. We show that the exploitation of the multipath enables us to resolve both azimuth and elevation with uniform linear arrays at single-frequency measurements. By using a uniform linear array of monopoles mounted on a metallic plate, we verify the results experimentally.

IEEE Transactions on Antennas and Propagation, 2000

Microstrip (patch) antennas usually strongly radiate in directions along the ground plane. This e... more Microstrip (patch) antennas usually strongly radiate in directions along the ground plane. This effect causes unwanted radiation patterns and increased coupling among array elements. Dielectric polarization currents are identified as physical sources of this radiation. A general technique is proposed to compensate these currents and suppress radiation in horizontal directions.