Ing. Tomáš Kořínek, Ph.D.

A novel approach to the evaluation of electromagnetic field radiated from devices by using a small shielded enclosure in presented. Several EMC problems can be identified by employing the computations of a Radiated Model device, such as the model the Submodule-on-Motherboard structure described here. The combination of a numerical approach, through a validation model and measurements, must be done during the design phase in multiple iterative loops to minimize the risk of non-compliance of the final qualification proces. Ths novel combined approach requires little investment and is highly efficient for industrial applications.

This paper describes the experimental verification of the utilization of long-term evolution (LTE) radio over fibre (RoF) and radio over free space optics (RoFSO) systems using dual-polarization signals for cloud radio access network (C-RAN) applications determining the specific utilization limits. A number of FSO configurations is proposed and investigated under different atmospheric turbulence regimes in order to recommend the best setup configuration. We show that the performance of the proposed link based on the combination of RoF and RoFSO for 64-QAM at 2.6 GHz is more affected by the turbulence based on the measured difference error vector magnitude value of 5.5 %. It is further demonstrated the proposed systems can offer higher noise immunity under particular scenarios with the signal-to-noise ratio reliability limit of 5 dB in the radio frequency domain for RoF and 19.3 dB in the optical domain for combination of RoF and RoFSO links.

Systém RFID lokalizátor umožňuje identifikovat oběti katastrof či zraněné osoby v definované oblasti. Systém zpracovává přenášené signály a do podrobné mapy zobrazuje v reálném čase polohu tagů, kterými jsou označeny oběti katastrofy či ranění. Řešení umožní optimalizovat postup záchranných prací a zároveň minimalizovat čas potřebný k záchraně, a to i v situaci, kdy jsou standardní komunikační systémy v důsledku katastrofy mimo provoz.

A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified via error vector magnitude statistics. Based on the results we show that transmitting of the LTE signal over the FSO channel is a potential solution for the last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.

The paper presents an RFID outdoor localization system that is able to locate hundreds of active transponders in the area od one square kilometer using three RFID receiving stations

The paper describes a design of global navigation satellite system (GNSS)/Radio frequency identification (RFID) active transponder which is primarily designed for localization of objects as a part of localization system designated for efficient handling of situations with mass casualties. The precise localization is improved by differential GNSS. The block diagram of such GNSS/RFID active transponder is described including main operation procedures of the firmware. Measurement of the localization by algorithms of RTKLIB library and by algorithms of GNSS module is compared. Dynamic tests, i.e. GNSS/RFID active transponder placed in the moving car (50~kmph), and static tests, i.e. GNSS/RFID active transponder placed in the position for 15~min, are performed.

Tests using three selected terrain diffraction models, three available experimental datasets and three digital elevation products with different horizontal and vertical resolutions were carried out to assess the role of input terrain profile in diffraction modeling. It is demonstrated that low-resolution terrain maps are not, generally speaking, suitable for terrain diffraction modeling. Further, it is also shown that utilizing digital elevation products with medium spatial resolution results in predictions close to the case when high-resolution terrain maps are considered. Index Terms—Digital elevation products, modeling, propagation,

A dual polarization (DP) radio over a free-space optical (FSO) communication link using a long-term evolution (LTE) radio signal is proposed and analyzed under different turbulence channel conditions. Radio signal transmission over the DP FSO channel is experimentally verified by means of error vector magnitude (EVM) statistics. Based on the results we show that transmitting the LTE signal over the FSO channel is a potential solution for the last-mile access or backbone networks, when using multiple-input multiple-output based DP signals.

This paper deals with the Ultra High Frequency (UHF) Radio Frequency Identification (RFID) tag design as a part of RFID localization system primarily designated for mass disasters. The design of RFID tag considers many casualties in an area of hundreds square meters, human body impedance, battery lifetime, maximal output power, resistant encapsulation etc. All requirements are taken into account in the design of several versions of RFID tag and the best one is chosen. Subsequently the design is manufactured and measured. Results show the designed RFID tag prototype is suitable for application in a disaster management.

In this paper, the first order statistics of co-polar components for a Land Mobile Satellite (LMS) channel for two scenarios, are investigated. The two scenarios refer to tree shadowing, one with the receiver placed inside an alley of trees and the second one with the receiver placed outside this alley of trees. For these two scenarios the received power for two orthogonal co-polar components was measured at Stromovka Park of Czech Republic using an airship. Due to the significance of first-order statistics of the signal envelope, using the measured power, four distributions are evaluated. More particularly, the Loo, Rice, Rayleigh and Lognormal distributions are investigated for modelling the Cumulative Distribution Function of the signal envelope for various elevation angles. It is found that Rice and Loo distributions have a very similar behaviour, while Rayleigh has the worst performance. Finally, some useful conclusions are drawn.

The Land Mobile Satellite (LMS) channel at 2GHz is examined and the first order statistics are modeled using experimental data for two tree shadowing scenarios. Considering that the first order statistics of the channel are used as input to channel models as well as for the calculation of the system margins, the modeling of the Probability Density Function (PDF) and the Cumulative Distribution Function (CDF) of the received signal envelope is of great importance for the design of LMS systems. Experimental data from measurements performed in Prague, the Czech Republic, are presented for two scenarios, a Heavy Tree Shadowing one and an Intermediate Tree Shadowing one. Four of the most widely used distributions, Rayleigh, Rice, Loo and lognormal, are considered for the modeling of the CDF of the signal envelope. Loo and Rice distributions out of the four considered distributions provide the best fit with reference to the measured data. Moreover, analytical empirical expressions are given for the parameters of the Loo distributions as a function of the elevation angle, to be used for the modeling of the LMS channel under tree shadowing. It is found that the expressions for the estimation of the distributions’ parameters provide a good fit to the experimental data.

he article describes the verification of the application of methods of network coding in the mobile wireless network environment with specific antenna system in use. Network coding principles are used for increase the reliability of data transmission. The proposed principles are demonstrated by modelling of the transmission system using data from real mobile networks. The effectiveness of network coding for deployment in wireless mobile networks is demonstrated on the basis of simulation in the simulation environment Omnet++. The input data of the simulation model are obtained by measuring in real mobile network of 2nd generation.

In response to the current need for a reliable interference and frequency coordination analysis, especially within the ground segment of satellite systems, atmospheric refraction and terrain diffraction phenomena play a key role from a radiowave propagation point of view. While it is convenient to use an ITU-R model for the case of the atmospheric refraction, several different types of models for terrain diffraction are identified in the literature. On the other hand, only a limited amount of experimental data is globally available to address their performance. This is why we carried out own short-term terrain diffraction measurements at the frequencies from L- to Q-band. During the trials, truck-mounted access platforms reaching up to 46 m above ground level were used and terrain profiles with path lengths from 7 km up to 50 km for various combinations of transmitter and receiver heights were addressed. Based on the obtained experimental dataset, the performance of the delta-Bullington and Deygout models, currently recommended by the ITU-R for the purposes of interference analysis, and the terrain diffraction models based on the UTD and parabolic equation approach has been addressed in terms of the testing variable defined in this paper.

Effects of window blind with metal-lamellas on radiowave propagation are addressed. Measurements of insertion loss at frequency range 5 - 50 GHz are presented. The measurements were done for various inclinations of lamellas of the window blind structure for both vertical and horizontal polarization. Comparison of measurements with numerical predictions is presented. The results give idea about additional insertion loss imposed by window blinds for indoor signal reception.

In this paper, we present first results of a shortterm measurement campaign aimed at terrain diffraction measurements. The campaign was held during August and September 2012 in the area of the Czech Republic and comprised using truck mounted access platforms to achieve a number of Tx and Rx station heights. Based on the experimental data obtained at frequencies ranging from L- to Q-band, a brief comparison between the measurements and selected propagation models is given as well.

Building penetration loss models presented in our previous paper [1] were valid for various scenarios, propagation conditions, frequency bands, and hemispherical receiving antenna pointing towards zenith. These models had a significantly rising trend of penetration loss with increasing elevation angle of the link in common. In this paper we show that when working with such non-isotropic terminal antennas, this trend relates primarily to the elevation trend of the reference level [2] dependent on the receiving antenna radiation pattern. This is demonstrated by the results of single-input multiple-output (SIMO) measurement trials performed at L-band in an office building and a brick building in the city of Prague. Further, based on the detailed analysis, a method to modify the elevation trend of a particular penetration loss model for different receiving antenna radiation patterns is derived and experimentally validated.

The paper discusses the emission spectroscopic measurement in the Fabry-Perot resonator. The presented results compare the spectra evaluated from the measured characteristics, obtained using various methods.

The chosen rectangular and fractal microstrip patch antennas above an infinite ground plane are analyzed by the Theory of characteristic modes. The resonant frequencies and radiation Q are evaluated. An method by G. Vandenbosch for rigorous evaluation of the radiation Q is employed for modal currents on a Rao-Wilton-Glisson (RWG) mesh. It is found that the resonant frequency of a rectangular patch antenna with a dominant mode presents quite complicated behaviour including having a minimum at a specific height. Similarly, as predicted from the simple wire model, the radiation Q exhibits a minimum too. It is observed that the presence of out-of-phase currents flowing along the patch antenna leads to a significant increase of the Q-factor.

Modal methods are used to effectively design a dual-band orthogonally polarized fractal patch antenna. This letter summarizes the workflow from generating a fractal motif through modal analysis to feeding design and full-wave analysis. As the antenna's feeding and matching structure, a dual L-probe was proposed to widen its bandwidth. The full-wave simulation is in very good agreement with the measurement. The motif size is 50 50 mm, and the antenna operates at 1.25 and 2.1 GHz. The relative bandwidths are 4.18% and 11.4%, respectively.

This article presents the methods of broadband axial feeding of a Fabry-Perot resonator. The resonator was originally designed with the radial excitation for the absorption measurement in the frequency band ranging from 18 to 80 GHz. If the frequency stays below ~26.4 GHz, the excitation of resonator is less satisfactory, since at the frequency in question, the value of Fresnel number of resonator drops to one. For the broadband measurement of gaseous samples' emission spectra, the excitations for frequencies lower than 26.4 GHz were analyzed using the capacitive coupling and two newly proposed couplings.

Modal methods are effectively used to design dual band fractal patch antenna. This contribution summarizes the workflow from generating fractal motif through choosing proper feeding to final antenna completion. As an antenna's feeding and matching structure, dual L-probe was proposed to widen its bandwidth. Moreover, the polarizations on operating bands are mutually orthogonal. This behavior is easily explained by modal decomposition of the surface currents. Antenna was fabricated and measured. © 2011 EurAAP.

The paper presents the broadband axial excitation of the Fabry-Perot resonator as well as its comparison with the standard radial excitation (via a dielectric foil) and two types of axial excitations (electric and inductive coupling) are discussed. The resonator was designed for the frequency range from 18 to at least 80 GHz. For the broadband measurement of the emission spectra, the excitation for the frequency range 18 - 26.5 GHz was proposed. Moreover, the excitations performance was measured and evaluated for the frequencies up to 40 GHz.

This paper presents preliminary results obtained from an extensive measurement campaign aimed at building penetration loss. We have concentrated on three different factors affecting this loss - the elevation, the frequency and the floor number of the investigated building. Results for two different measurement sites at 2.0 GHz and 5.0 GHz inside an old brick three-storey office building located in Prague are provided together with a brief description of the measurement system used during the measurement campaign.

The paper describes the heterodyne detector suitable for the microwave spectroscopy. At the lower frequencies (from the spectroscopic point of view), the measured gas is commonly saturated and the absorption measurement is impossible. The discussed heterodyne detector can measure with high dynamic range exceeding 90 dB. In addition, it enables to measure the weak signals or even very low changes in strong signals.

A new antenna measurement system has been implemented in an antenna anechoic chamber at the Czech Technical University in Prague. The article contains the system overview, it brings the results of the first measurements and it shows the system improvements.

The Fourier Transform Microwave Spectrometer (FTMW) is subject to simplification by means of the spectral analyser, instead of the super-heterodyne receiver. The paper is focused on the FTMW arrangement, the procedures of the resonator tuning and optimization of the excitation impulse length. In the paper, the virtues of the FTMW technique are demonstrated on the comparison of the emission and the absorption spectra.

The aim of this paper is to describe tree attenuation measurements at 2 GHz in four different locations inside vegetation, and at three different positions for a single tree shadowing. The purpose of this measurement campaign was to use a 9-meter long remote-controlled airship as a pseudosatellite. The transmitting station was located on the airship as a payload and receiving station inside or nearby the vegetation. Subsequently, the received signal strength was measured at each position as a function of elevation angles ranging from 25 to 90 degrees. Measurements taken in an open field were used as a reference. The measured data are still being processed, however, the initial results are shown. The results for locations inside the vegetation and the single tree are compared as well.

Two prototypes of human head protective hood were developed in the project called BE-TEX "Human and technology protection against high frequency radiation - research and development of new textiles". Interesting results of shielding efficiency were achieved by specially prepared yarn and suitable construction of full face hood. The shielding efficiency defines an attenuation of high frequency signal after spill by shielding material. Measurement results were gained in 500 MHz frequency range. Electric field intensity was compared for situations with ad without fool head hood.

A simple Fabry-Perot interferometer was used for measurements of microwave spectra. Both basic experimental arrangements, absorption and emission, were tested on the rotational spectra of acetonitrile. The interferometric results obtained were compared with the spectra measured using a standard high resolution microwave spectrometer.

The authors attention has been focused on the design items that are most crucial by the achievement of satisfactory value of the VSWR and the impedance matching at the feeding ports in the extended frequency range from 80 MHz to 1000 MHz. For this purpose, the Vivaldi-structure and other advanced structures were considered. The theoretical approach based on numerical simulations lead to conclusions which have been applied by the physical design and also evaluated by experimental results.

This work deals with a shielding effectiveness measurement of small enclosures. The main aim of this work is to highlight drawbacks and advantages of various so far utilized measuring approaches. There are many problems, which have strong influence on measurement results - type of antennas, position of antenna inside the enclosure, measurement of references (in open area or with open door of enclosure), influence of different objects inside the enclosure, location of generator (inside or outside of enclosure), problem of reciprocity theorem. These aspects were investigated by analyses via EM simulation software FEKO and experimental measurements.

This paper describes the special EMC issue which emerges during shielding effectiveness measurement of relatively (compare to the wavelength) small enclosures. The main aim of this paper is to show difference of the shielding effectiveness values in dependence on different types of used measuring linearly and circularly polarized antennas.

Knowledge of the cutoff frequencies of modes in nonstandard double ridged waveguides is extremely important for determination of operation bandwidth for design of broadband structures. It is shown that for nonstandard dimensions of the ridged waveguide the TE30 mode doesn't exist or is degenerated or the higher mode skips the TE30 mode. Strategy of the complex broadband double ridged horn antennas design (coaxial - waveguide transitions, impedance transformers, radiated ridged and horn structures etc.) is mentioned and as an example the 4-40GHz antenna is presented.

The evaluation of the Shielding Effectiveness (SE) brings great challenges from the EMC measurement point of view. Particularly in the case of measurement of small enclosures, many different approaches can be used. Therefore, based on an extensive measurement campaign, various aspects of measurement of the shielding effectiveness of small metallic enclosures were investigated. Significant results of this campaign are discussed in this paper.

The aim of this paper is to introduce options for measurements conducted at the CTU Prague using a low altitude airship. Experiments were proposed in the 3G and millimetre frequency bands. An example of measured data at the 2 GHz frequency is presented. An overview of planned experimental work is given. The goal is to obtain experimental data that can be used to plan communication systems delivered via High Altitude Platforms (HAPs).

For some ultra wideband applications (i.e. radar, positioning, etc.), it is crucial to know the transient responses of antennas. Optimization process searches for the dipole shape, which accomplishes two required parameters - namely good matching and minimal distortion. The dipoles have derivative characteristics. The distortion is evaluated from the derivative of the excitation impulse with the radiated impulse. The particle swarm optimization method was used in the process of optimization. This method was implemented in MATLAB(R), where the antenna structure is generated. The antenna is ubsequently simulated in the CST Microwave Studio(R). The optimized ultra wideband dipole is perfectly matched and minimally distorts the applied signal.

Small shielded boxes are nowadays widely used for measurement of EMS, EMI and sensitivity properties of different devices. This paper deals with an improvement of commercial small shielded box parameters for a measurement of sensitivity of small mobile devices in 650 MHz - 4 GHz frequency band. Optimization of shielded box parameters is obtained by an inner area modification. Suitable wideband equiangular spiral antenna was designed for this measurement. Parameters of antenna inside the box, such as gain, impedance, directivity etc. are discussed in the paper. Effects of antenna positions in the box for a transmission are shown and the best configuration of antennas placing for the transmission in the shielded box is chosen.

The paper describes a design of planar five-element Yagi-Uda antenna for 2,4 GHz band. The structure has been optimized for a maximum directivity and maximum front-toback ratio by planar simulator IE3D. Special feature of the antenna are reflector formed by ground plane edge and solution of impedance symmetrization and matching. Antenna has been realized and measured. Comparison of simulated and measured data are also presented.

The paper presents a comparison of planar Yagi-Uda antenna simulation performed by two different planar simulators. The simulations have been done by planar simulator IE3D that uses integral equation/method of moment (IE/MoM) analysis in frequency domain and by planar simulator CST Microwave Studio that uses method of finite difference time domain analysis (FDTD). Comparisons of simulated and measured data are also presented.