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The interest for spherical arrays is based on their possibility to direct single or multiple beams through complete hemisphere. In this article, circular stacked-patch antennas embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. The influence of structure radius on input impedance, mutual coupling and radiation pattern is investigated...
This paper outlines a multiband antenna design based on fractal concepts. Simulation studies to investigate the influence of fractals on resonant frequencies are presented. The numbers of fractals are varied and influence on frequency bands is observed
Development of information technology nowadays allows to use computer resources for modeling and investigation of different processes as well as for teaching. Computer simulation makes easy investigation of different processes and models of physical devices. The paper means to inform about the new non-standard method of teaching - that is the method of virtual laboratory classes
The file has been describing failure studies as well as repair analyses of optical networks installed within telecommunication network on transport network level. Data collected in the longer period of time have been analysed with regard to failure type, causes, frequency intensity and repair intensity. Collected data were compared to the owner of similar optical networks. The failure rates was calculated,...
The paper deals with the theoretical and methodological background for the time-domain (TD) study of complex open resonant structures. We discuss the formulation and solution of model initial boundary-value problems of the theory of open resonators (OR), the analytical relations between spatial-temporal and spatial-frequency representations for the solutions, the problem of choice of the pulse source...
The paper makes an analysis of the propagation of HF radio signal in a tropical region. The propagation of HF radio signal through the ionosphere is used widely in Nigeria, most especially within the airports. This paper surveys and highlighted the problems experienced by HF radio signal in its journey through the special ionosphere of a tropical region. Based on purely technical consideration, the...
Despite the development of a wide variety of antenna modeling codes, including a large number of commercial ones that are of excellent quality, the design of communication and radar antennas - both large and small - continue to challenge us because of their multiscale and complex nature. In this paper we will discuss a number of antenna modeling and design problems that we have encountered in recent...
In this paper we propose a simplified model for studying the Brillouin diagrams based on dielectric multilayers inside a parallel plate waveguide. The main objective of this work is the use of a simplified approach in modelling EBG structures with periodical defects. The effect of layer permittivity, defect length and periodicity were studied using simulation software with appropriated periodical...
Free space microwave measurements are reported of a split ring and post type metamaterial that exhibits negative index of refraction in a frequency band near 13.5 GHz. Varying azimuthal angles and magnitudes are achieved by changing the polarization of the transmitter and receiver relative to each other and to the anisotropic material. The amplitude of the cross-polarized transmission has been measured...
Basic radiation properties of a rectangular waveguide filled with anisotropic, either mu-negative (MNG) filling or epsilon-negative (ENG) filling are investigated experimentally. Two antennas based on waveguides filled with double-ring resonators (an MNG filling) and thin wires (an ENG filling) were designed, manufactured and measured in 8 GHz band. It was found that although these waveguides may...
Previously proposed 2D isotropic split ring resonators are analyzed. Furthermore, a new isotropic 3D particle is proposed and analyzed. To this end a quasi-static LC circuit model, that provides the frequency of resonance, is developed. Theoretical computations of resonant frequency are in good agreement with the values obtained with a commercial electromagnetic solver. Finally the complete isotropy...
This paper describes how it is possible to increase the radiation bandwidth and the gain of a classical planar EBG antenna. Those two parameters are relative to the EBG material but also to the excitation, this second characteristic is studied here. The principle is to excite the EBG structure with several sources (instead of a single one classically). The performances depend on the number of sources...
In this contribution, we review the analysis of metamaterial grounded planar bilayers supporting leaky-waves, which we have recently proposed elsewhere as compact sub-wavelength leaky-wave radiators, and for enhancing the wave transmission through apertures over conducting screens when used as covers. Exploiting the peculiar resonances arising when "complementary" or "conjugate"...
The aim of this contribution is to analyze the sub-diffraction image formation and detection in metamaterial super-lenses. It is shown that, owing to the evanescent nature of the involved electromagnetic fields, the image detection process can yield quite different results from those expected from the image formation theory. In particular, it is shown that, under some circumstances, an appropriate...
In this paper, small-sized RFID tag antenna is designed and fabricated based on the circular loop antenna used in UHF band (860-960 MHz). The tag antenna with its center frequency at 911.25 MHz (wave length lambda: 329 mm) adopts a parallel transmission line feed method to match the impedance and reduces its size using a stub. As a result, the antenna (diameter lambda: 54 mm) with 15 stubs reduces...
Within a few years, the use of mobile - called "cellular" - phones exploded all over the world. More than 600 millions of them were sold in 2004! To ensure proper service, base stations must be installed in increasing numbers and many people strongly object to seeing antennas sprouting up in their close neighbourhood! So far, no one has been able to definitely prove that radiation from cellular...
We discuss several types of potential instabilities in nonlinear electronic circuits due to sub- and ultra-harmonics generation, as well as intermodulation distortions caused by either multi-frequency input signals or coupling between intrinsic oscillatory modes. The limitations of traditional approach used for the circuit analysis in the time domain, like, e.g., harmonic balance or small-signal analysis...
The paper describes the examples in teaching electromagnetics at the Czech Technical University in Prague. Due to the abstract nature of electromagnetics, computer simulations play an important role here. The paper describes the way of the efficient incorporation of simulations to the teaching process. We emphasize the simulations have to be deeply analyzed together with students to improve their...
A rapid development of communication technologies requires electrical engineers to be continuously educated. Due to the high time demands of their jobs, employers ask technical universities to prepare e-learning courses accessible via Internet. The paper presents two Internet textbooks covering the area of analysis and optimization of microwave structures. Discussion is turned to structuring textbooks,...
Due to the global status of today's electronics industry, prospective employees educated by technical universities are expected to be able working in multi-national teams, attending international courses of highly specialized education, effectively sharing their knowledge and abilities. In order to prepare students to the described situation, approximately 20 European universities have organized the...
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