ISSN 1210-2512 (Print)

ISSN 1805-9600 (Online)

Radioengineering

Radioeng

Proceedings of Czech and Slovak Technical Universities

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December 2009, Volume 18, Number 4

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G. A. E. Vandenbosch [references] [full-text] [Download Citations]
Efficient Procedure for the Calculation of Electric and Magnetic Energies in Vacuum

New expressions are derived to calculate the reactive energy stored in the electromagnetic field surrounding an electromagnetic device. The resulting expressions are 1. very simple to interpret, 2. general, 3. rigorous in terms of the currents flowing on the device, and 4. fast since they involve integrals solely over the device generating the field. The new technique is very feasible to be used in cases where the electric and magnetic reactive energies are important in practice, for example in the case of resonators, or in the case of radiating structures. Used there, they allow to study in a rigorous way the effect of the shape of the device on the amount of reactive energy, and thus for example on the Q of the device. The implementation of the new expressions in numerical CAD tools is extremely simple and straight-forward. In this paper, the expressions are derived for sources in the homogeneous medium vacuum, but this is not a fundamental restriction.

Keywords: Electric and magnetic energy, Q factor, small antennas.

S. R. Best [references] [full-text] [Download Citations]
The Quality Factor of the Folded Cylindrical Helix

Any electrically small antenna can be impedance matched at any single frequency using a number of well known techniques. Once the small antenna is impedance matched, the primary characteristics of interest are its radiation efficiency, its operating bandwidth and to a lesser extent, its radiation patterns. The bandwidth of the small antenna is often quantified using the antenna's quality factor (Q) since fundamental lower bounds for Q are defined in terms of the antenna's occupied volume. The lower bound on Q, also known as the Chu-limit, is defined in terms of the spherical volume occupied by the antenna. However, many small antenna designs are constrained to fit within volumes other than a sphere. To address this issue, Gustafsson et al derived lower bounds for antennas of arbitrary shape with a specific focus on cylindrical and planar shaped antennas. In this paper we consider the quality factor of the folded cylindrical helix, an antenna design that effectively utilizes the available cylindrical volume. We compare its Q to the Gustaffson limit as a function of length-to-diameter ratio, while maintaining a fixed value of ka, and show that it’s Q is at or above Gustafsson’s lower bound for cylindrical shaped antennas.

Keywords: Electrically small antennas, quality factor, dipole.

D. Rialet, A. Sharaiha, A. Tarot, X. Castel, C. Delaveaud [references] [full-text] [Download Citations]
Characterization of Antennas on Dielectric and Magnetic Substrates Effective Medium Approximation

This paper presents a study of the effective medium approximation of a monopole antenna printed on either a dielectric or a magnetic substrate. Simple analytical formulas to determine the effective permeability of such an antenna have been proposed and validated. For this type of antenna as μr increases, the effective permeability will reach the value of 2 (maximum) whereas, with the dielectric substrate, the effective permittivity continues to rise when increasing εr. This shows that, for very high permeability values, we will always have a size reduction below 30%.

Keywords: Antennas on dielectric and magnetic substrates, effective medium, analytical model.

S. V. Shynu, M. J. Roo-Ons, M. J. Ammann, B. Norton [references] [full-text] [Download Citations]
Dual Band a-Si:H Solar-Slot Antenna for 2.4/5.2GHz WLAN Applications

A simple and compact design of solar-slot antenna for dual band 2.4/5.2GHz wireless local area networks (WLAN) applications is proposed. The design employs amorphous silicon (a-Si:H) solar cells in polyimide substrate with an embedded twin strip slot structure to generate dual resonant frequencies. A T-shaped microstripline feed is used to excite the twin slot in the a-Si:H solar cell. The measured impedance bandwidths for the proposed solar antenna are 25.9% (642 MHz) centered at 2.482 GHz and 8.2% (420 MHz) centered at 5.098 GHz. The measured gain at 2.4 and 5.2 GHz are 3.1 dBi and 2.1 dBi respectively.

Keywords: Solar antenna, slot antenna, amorphous silicon.

J. Abadia, F. Merli, J. Zurcher, J. R. Mosig, A. K. Skrivervik [references] [full-text] [Download Citations]
3D-Spiral Small Antenna Design and Realization for Biomedical Telemetry in the MICS band

This work presents the design and realization procedure of small implantable antenna for biotelemetry applications. The radiator occupies a volume smaller than 3 cm3 (without its biocompatible insulation), is well matched within the Medical Implanted Communications System band and shows an adequate gain (-28.5 dB) while introduced in the appropriate equivalent body medium. The latter is a homogeneous phantom with muscle dielectric properties. A prototype has been manufactured and measurements agree with theoretical predictions. Particular attention is paid to the building requirements such as the presence of glue. Specific Absorption Rate (SAR) distribution has been computed evaluating the maximum power deliverable to the antenna in order to respect the regulated SAR limitation.

Keywords: Electrically Small Antenna (ESA), implantable antenna, Medical Implant Communications Services (MICS), Medical Device Radiocommunication Service (MedRadio), biocompatible antenna.

M. Polivka, D. Vrba [references] [full-text] [Download Citations]
Shielded Micro-Coplanar CRLH TL Zeroth-Order Resonator Antenna: Critical Performance Evaluation

The attention of this paper is focused on the four unit cell zeroth-order resonator antenna (ZORA), manufactured on a shielded micro-coplanar composite right/left-handed (CRLH) transmission line structure. The antenna was designed to achieve a broadside patch-type radiation pattern. The dimensions of the antenna element follow: 15.6 x 9.35 x 3.1 mm (i.e. 0.27 x 0.16 x 0.05 λ0 at the measured zeroth-order resonance f0 = 5.14 GHz) with the shielded plane of the size of 60 x 40 mm (approx. 1.0 x 0.7 λ0). The measured gain and the antenna efficiency are equal to 4.6 dBi and 48 %, respectively. The performance of the proposed ZORA is subject to critical evaluation based on the comparison with the reference quarter-wavelength patch antenna (QWPA) that has the same dimensions. It has been found that ZORA provides comparable or even better parameters to those of QWPA, except of the bandwidth, which is much narrower in case of ZORA. In comparison to QWPA, the main advantage of the proposed ZORA might be then seen in the possibility to produce the entire ZORA structure by means of the integrated microstrip technology with air bridges. In contrary to it, the fabrication of the QWPA requires the use of either the foam substrate or plastic support pins or the application of ridged self-supporting metal plates.

Keywords: Antenna efficiency, composite right/left-handed transmission line, patch antenna, radiation efficiency, zeroth-order resonator.

S. Sufyar, C. Delaveaud [references] [full-text] [Download Citations]
A Miniaturization Technique of a Compact Omnidirectional Antenna

This paper discusses a miniaturization technique of a compact omnidirectional antenna. A slot loading technique is applied to a well-known low-profile antenna structure whose radiation characteristics are similar to equivalent monopole ones. An equivalent circuit which models the antenna input impedance including the slot effect is also developed in order to illustrate the antenna working principle. The typical dimensions (width x height) of the obtained antenna are λ0/11 x λ0/75 (λ0 is the free space operating wavelength) which makes it a miniature antenna that can be integrated inside small wireless sensor nodes using narrow band communication systems. Its performances are in accordance with classical fundamental limits, the operating bandwidth and efficiency are significantly reduced with the antenna size reduction.

Keywords: Omnidirectional radiation, loading, fundamental limits. miniaturization, slot

L. Guo, X. Chen, C. Parini [references] [full-text] [Download Citations]
Study of a Miniaturized Quasi-Self-Complementary UWB Antenna in Frequency and Time Domain

A compact antenna for UWB communication systems has been realized by employing a quasi-selfcomplementary structure together with a triangular notch on microstrip feed line in this paper. The optimal design of this type of antenna can offer an ultra wide return loss bandwidth with reasonable radiation properties. It features a quite small physical dimension of 16 mm x 25 mm, corresponding to an electrically size of 0.24 λ. A good agreement is achieved between the simulated and the measured antenna characteristics. The major parameters that influence the performance of the antenna are investigated numerically to gain an insight into the antenna operation. Time domain performance of the antenna is also examined in order to assess its suitability for impulse radio applications.

Keywords: Antenna transient analysis, self-complementary antennas, small antennas, UWB antennas.

B. Ivsic, D. Bonefacic, J. Bartolic [references] [full-text] [Download Citations]
Reconfigurable Pico-cell Antenna Array for Indoor Coverage in GSM 900 Band

This paper proposes a simple antenna array based on three stacked shorted patches aimed to be used as GSM (900 MHz) indoor base station antenna. Three same linearly polarized stacked patches are set in three orthogonal planes in space forming pyramid-like structure. The antenna array can be used for nearly omnidirectional coverage as well as for covering three 120º sectors. The proposed array also offers the possibility of polarization diversity.

Keywords: Antenna size reduction, small antenna, shorted stacked patch, indoor coverage, sector coverage.

D. Manteuffel, M. Arnold, P. Uhlig [references] [full-text] [Download Citations]
Considerations on Configurable Multi-Standard Antennas for Mobile Terminals Realized in LTCC Technology

This paper is an extended version of a paper presented at the EuCAP 2009 conference [1]. We present part of a long term research project that aims on designing a (re-)configurable multi-standard antenna element for 4G (4th Generation) mobile terminals based on LTCC (Low Temperature Co-fired Ceramic) technology. The antenna itself is a coupling element [2] that efficiently excites the chassis of the mobile terminal to radiate as an entire antenna. Coupling is optimized by a reactive tuning circuit. Several of these tuning circuits are realized in a single LTCC component and can be multiplexed to the antenna by a SPnT (Single Pole n Thru) antenna switch integrated into the LTCC component. The coils and capacitor in the LTCC component are configurable on the top-layer of the component. Thus, the component is configurable according to different mobile terminal chassis configurations and multiple bands.

Keywords: LTCC, reconfigurable antenna, coupling element, 4G antenna, small terminal antenna.

N. Guan, K. Ito [references] [full-text] [Download Citations]
A Compact Wideband Two-Arm-Antenna for Mobile Phones

A compact film type antenna capable of generating two wide resonant modes for covering the AMPS/GSM bands and the DCS/PCS/UMTS bands for mobile phones is proposed. The antenna consists of two superimposed radiation arms which can support two resonant modes by themselves. The frequency range of a resonant mode generated by one of the arm is arranged to differ a little with the corresponding mode of the other, at the fundamental and higher-order modes. As a result, the bandwidths at both of the resonant modes are significantly enhanced. The antenna has a compact dimension of 5 x 15 x 40 mm3 and covers five bands of AMPS/GSM/DCS/ PCS/UMTS for a VSWR less than 2.5:1. It shows fairly good omnidirectional radiation patterns and high gains over 0 dBi in the azimuthal plane, at all the operating bands.

Keywords: Multi-band antenna, compact antenna, mobile phone.

F. Ferrero, A. Diallo, C. Luxey, B. Derat, P. Hamouz, P. Hazdra, J. Rahola [references] [full-text] [Download Citations]
Two-Element PIFA Array Structure for Polarization Diversity in UMTS Mobile Phones

In this paper, we demonstrate the possibility to strongly modify the radiated fields of a UMTS handset by using a phased two-element PIFA array. The structure is composed of a 100x40 mm2 metallic ground plane acting as the Printed Circuit Board (PCB) of the mobile phone. Two UMTS PIFAs are located at the top edge of this PCB. They are fed by a double Quasi-Lumped Coupler able to provide a 360° phase difference between its two outputs. By properly choosing the DC bias of the double QuasiLumped Coupler, we can set a specific phase difference between the two PIFAs. In this way the two-element array is able to radiate different electromagnetic fields. Simulated and measured radiation patterns in the two main planes of the chassis are presented for different phase differences. It is especially revealed that the novel twoantenna structure is able to radiate vertically-polarized electric fields in the azimuthal plane of the phone and horizontally-polarized electric fields in the same plane when changing the phase shift between the antennas from 0° to 180°. Potential applications are polarization-diversity techniques and Specific Absorption Rate reduction for handsets.

Keywords: Planar Inverted-F Antennas, UMTS Mobile Phones, Polarization Diversity.

H. Arai, J. Ohno [references] [full-text] [Download Citations]
Channel Capacity Enhancement by Pattern Controlled Handset Antenna

This paper presents a radiation pattern controlled antenna for handset terminals to reduce the correlation coefficient between antennas and enhance the channel capacity in MIMO applications. A pair of small inverted-F shaped antennas combined by a phase shifter provides a single port with controlled pattern. To enhance the channel capacity, the phase difference for the IFA array is optimized using the evaluation parameter of reception level, correlation coefficient and mean effective gain of the proposed array geometry. The channel capacity enhancement is verified by assuming Croneker scattering under Nakagami-Rice propagation model.

Keywords: eywords MIMO, inverted-F shaped antenna, channel capacity, correlation coefficient, MEG.

J. Guterman, A. Moreira, C. Peixeiro, Y. Rahmat-Samii [references] [full-text] [Download Citations]
Antenna-User Interaction in MIMO-Enabled Laptops

The operation of wireless personal communication terminals very close to the user inherently faces the problem of electromagnetic (EM) coupling between the device and the biological tissues. In this paper the effects of the electromagnetic antenna-human interaction is studied for a laptop MIMO antenna system, where four integrated antenna elements can operate simultaneously. Two points of view are considered: antenna performance and EM dosimetry. The first one addresses not only the degradation of the antenna performance but includes also the effect of the human proximity on the antenna characteristics, namely scattering matrix, Total Active Reflection Coefficient (TARC), radiation efficiency and envelope correlation between port signals. The exposure of the human tissues to EM radiation is expressed in terms of Specific Absorption Rate (SAR). These characteristics are evaluated as a function of the array excitation scheme (including phased array approach and MIMO-like signaling) and compared to simple scenarios where all the power is radiated only by one antenna element.

Keywords: Laptop antennas, MIMO antenna systems, TARC, SAR, EM dosimetry.

E. Antonino-Daviu, M. Cabedo-Fabres, M. Ferrando-Bataller, M. Gallo [references] [full-text] [Download Citations]
Design of a Multimode MIMO Antenna Using the Theory of Characteristic Modes

In this communication, the design procedure of a multimode Multiple-Input Multiple-Output (MIMO) antenna is presented. The antenna consists of a metallic ring antenna operating with different orthogonal modes, whose performance in a MIMO system is similar to traditional antenna arrays. Thus, a compact MIMO antenna is obtained, which is very suitable for mobile terminals. A modal analysis of the antenna is carried out first by means of the Theory of Characteristic Modes, in order to identify the different radiating modes of the antenna. Then a set of feeding configurations is proposed so as to excite these modes. As the modes must operate in the same frequency band, a loading technique is used in the antenna in order to shift the resonance frequency of the modes to the proper band.

Keywords: Antenna design, multimode antenna, MIMO, multiple feed, capacitive loading.

R. Serrano, S. Capdevila, A. Aguasca, J. Romeu, L. Jofre [references] [full-text] [Download Citations]
Multiport Multiband Decoupling Optimization for Miniature Antennas

Multiband multiport antennas are increasingly used for wireless communications and sensing miniature devices. The equations governing the multiport multiband antennas are analyzed in this paper with the objective of drawing the design guidelines for low coupling small antennas. Those guidelines have been applied in the design and optimization of a two-port dual band small antenna of size around λ0/13 x λ0/13 at the lowest frequency. Certain coupling conditions are applied to the port loads achieving a coupling reduction of 8 dB when having a simple two-element real load. A reduction of 27 dB can be obtained when having ideal loads composed by a higher number of elements. The antenna geometry is shown together with coupling minimization results.

Keywords: Multiport multiband antennas, miniature antennas, decoupling, S-parameters, efficiency.

K. Karlsson, J. Carlsson [references] [full-text] [Download Citations]
Circuit Based Optimization of Radiation Characteristics of Single and Multi-Port Antennas

A method for analyzing and optimizing multiport antennas is presented and exemplified. The method was first presented in [1]-[3] and uses data from full wave electromagnetic field (EM) solvers in combination with circuit simulations for efficient calculations of radiation properties of multi-port antennas. The main advantage of the proposed method is that only a few full-wave simulations, which usually are time consuming, are needed when e.g. optimizing the matching circuits for a multi-port antenna. Since embedded element patterns are used, all relevant antenna parameters such as radiation efficiency, diversity gain, available MIMO capacity etc. can efficiently be computed for any port excitation and loading configuration. The methodology has been implemented in software called MPA (Multi-Port Antenna evaluator) which imports port response matrices and embedded element patterns from commercial full-wave codes and post processes the data making it possible to e.g. optimize capacity for a MIMO system. The optimization is done by changing the feeding and matching networks in a circuit simulator that is invoked by the MPA. Finally the software is used on two examples which are analyzed and optimized to illustrate the potential of the method.

Keywords: Embedded element pattern, optimization, multi-port antenna, antenna efficiency, antenna diversity, impedance matching.

C. Volmer, R. Stephan, M. A. Hein [references] [full-text] [Download Citations]
Evaluation of a Mutually Coupled Diversity Receiver

A quick, reliable, and simple evaluation of mutual coupling effects is essential for the optimization of antenna arrays for small mobile communications devices. In recent papers we have proposed novel figures of merit that quantify the impact on diversity reception in terms of scattering matrix of the array and have confirmed the validity of these formulas by practical diversity measurements. The present paper provides an extended analysis of the measurement data and contrasts the benefits of this method of array characterization with existing approaches.

Keywords: Mutual coupling, antenna diversity, decoupling and matching network.

C. Orlenius, M. Andersson [references] [full-text] [Download Citations]
Repeatable Performance Measurements of MIMO Systems in Connected Reverberation Chambers with Controlled Keyhole Effect

A straightforward, fast, and repeatable procedure for measuring the system performance of the antennas in a MIMO system is presented. Due to the use of two connected reverberation chambers, the so called keyhole effect is observed and can be controlled. The method is possible to use for performance measurements of complete MIMO systems, and the present paper lays out the basics for making this possible.

Keywords: Reverberation chamber, Multiple-Input-Multiple-Output, MIMO, antenna characterization.

L. J. Foged, A. Scannavini [references] [full-text] [Download Citations]
Efficient Testing of Wireless Devices from 800 MHz to 18 GHz

Small antennas and other modern communication applications are using increasingly higher frequencies while demanding shorter development time and very rapid testing cycles. A fast and accurate way to exhaustively determine antenna performance and/or investigate device malfunction is based on spherical near field measurement techniques combined with probe array technology.
This paper describes the innovative design aspects of the StarLab portable antenna measurement system and present results from the validation campaigns including both passive and active measurements. The use of integrated diagnostic and analysis software modules for efficient antenna design and testing is also presented.

Keywords: Antenna Measurements, Spherical Near Field, Probe Array, Small Antennas, OTA (over-the-air) measurements, TRP (Total Radiated Power), TIS (Total Radiated Sensitivity), CTIA (Cellular Telecommunications and Internet Association), 3GPP (3G Partner Part

K. B. Baltzis [references] [full-text] [Download Citations]
Impact of Finger Placement on the Correlation Properties of Rake Combined Signals

3G mobile devices and base stations employ rake receivers. An important issue in the design of such receivers is finger allocation. This paper explores the relationship between finger placement and the correlation properties of rake combined signals. The dependence of correlation coefficients on system parameters such as the multipath characteristics of the propagation channel, the number of users, the processing gain and the thermal noise power is also discussed. Several conclusions useful in the analysis and design of rake receivers are drawn. A low complexity finger placement algorithm is finally suggested. In the proposed receiver, finger allocation is based on the correlation properties of the desired signal component only. The receiver performs close to complex structures in the literature.

Keywords: Rake receiver, correlation, spread spectrum, mobile communications, multi-objective optimization

P. Kejik, S. Hanus [references] [full-text] [Download Citations]
Enhanced Receivers for Interference Cancellation in 3G Systems

Interference cancellation and multiuser detection in CDMA systems are still actual research topics. These techniques enable us to deal with interference and to increase system capacity. In this paper, a so-called Generalized RAKE receiver, an Uplink generalized multiuser detection and a Blind adaptive multiuser detection are described. These algorithms are compared with conventional receivers and their properties are verified via simulations. The results imply that some of these algorithms are able to overcome the performance of the conventional receivers.

Keywords: Interference cancellation, multiuser detection, CDMA, G-RAKE.

P. Kadlec, P. Kejik, Z. Raida [references] [full-text] [Download Citations]
Comparison of Pilot Symbol Embedded Channel Estimation Algorithms

In the paper, algorithms of the pilot symbol embedded channel estimation are compared. Attention is turned to the Least Square (LS) channel estimation and the Sliding Correlator (SC) algorithm. Both algorithms are implemented in Matlab to estimate the Channel Impulse Response (CIR) of a channel exhibiting multi-path propagation. Algorithms are compared from the viewpoint of computational demands, influence of the Additive White Gaussian Noise (AWGN), an embedded pilot symbol and a computed CIR over the estimation error.

Keywords: Channel estimation, Least Squares, Sliding Correlator, AWGN channel, Hadamard function.

P. Lafata, J. Vodrazka [references] [full-text] [Download Citations]
Modeling of Transmission Functions and Crosstalk in Metallic Cables for Implementation of MIMO Concept

The new promising wireless networks based on multi-carrier modulations (MCM) and multiple-input multiple-output concept (MIMO) will soon offer high-speed digital connections. Their access points are mostly connected by fixed metallic lines to core data and telecommunication networks. That is why it will also be necessary to increase the transmission speed and overall performance of these fixed access networks adequately in order to meet the expected requirements of wireless connections. It would be possible to use VDSL2 digital subscriber lines and implement MIMO concept into the existing metallic networks for this purpose, but before that it will be necessary to solve several problems first. The transmission capacity of present VDSL2 digital lines is limited mainly by crosstalk occurring in metallic cables. This paper describes a new method for modeling of transmission functions and crosstalk in multi-pair and multi-quad metallic cables including its mathematical implementation, and it also gives an example of results obtained so far. The presented model is based on statistical evaluations of measured values, generation of pseudo-random components of frequency response and subsequent filtration process.

Keywords: Multi-carrier modulation, multiple-input multiple-output, vectored DMT modulation, crosstalk, modeling.

L. Liu, C. Tao, J. Qiu, X. Qi [references] [full-text] [Download Citations]
A Novel Comb-Pilot Transform Domain Frequency Diversity Channel Estimation for OFDM System

Due to implementation complexity, the transform domain channel estimation based on training symbols or comb-type pilots has been paid more attention because of its efficient algorithm FFT/IFFT. However, in a comb-type OFDM system, the length of the channel impulse response is much smaller than the pilot number. In this case, the comb-pilot transform domain channel estimation only works as interpolation like the Least Squares (LS) algorithm, but loses the noise suppression function. In this paper, we propose a novel frequency diversity channel estimation method via grouped pilots combining. With this estimator, not only the channel frequency response on non-pilot subcarriers can be interpolated, but also the noise can be better suppressed. Moreover, it does not need prior statistical characteristics of the wireless channel.

Keywords: Channel estimation, transform domain, orthogonal frequency division multiplexing (OFDM), noise suppression.

V. Wieser, V. Psenak [references] [full-text] [Download Citations]
Performance of Predictor Based Link Adaptation Algorithms

The presented paper deals with the link adaptation algorithms in mobile radio access networks based on Wideband Code Division Multiple Access (WCDMA). The mobile radio channel has a significant impact on the transmitted signal between User Equipment (UE) and Base Station (BS). The character of environment (e.g. number of received reflections) and increasing UE velocity cause unfavorable signal fadings, which have a major impact on the received signal. Due to this fact and the principle of WCDMA, fast power adaptation is essential for mobile radio access networks based on WCDMA. The prediction of mobile radio channel near-future state is one of the possible approaches how to span its unfavorable state. According to this assumption, we have improved the basic link adaptation algorithm (used to control properties of transmitter) to predictor based link adaptation algorithm. This contribution comprises the performance of basic link adaptation algorithm and predictor based algorithms, which support both variable (multi-bit) and fixed (singlebit) power steps to modify transmitter output power level. The link adaptation algorithms were simulated under various average UE velocities in urban environment. New algorithms were designed to increase the efficiency of data transmission in uplink direction.

Keywords: WCDMA based mobile radio access networks, link adaptation, prediction methods, mobile radio channel.

H. Yang, X. Sun, G. Sun [references] [full-text] [Download Citations]
A High-Capacity Image Data Hiding Scheme Using Adaptive LSB Substitution

Many existing steganographic methods hide more secret data into edged areas than smooth areas in the host image, which does not differentiate textures from edges and causes serious degradation in actual edge areas. To avoid abrupt changes in image edge areas, as well as to achieve better quality of the stego-image, a novel image data hiding technique by adaptive Least Significant Bits (LSBs) substitution is proposed in this paper. The scheme exploits the brightness, edges, and texture masking of the host image to estimate the number k of LSBs for data hiding. Pixels in the noise non-sensitive regions are embedded by a k-bit LSB substitution with a lager value of k than that of the pixels in noise sensitive regions. Moreover, an optimal pixel adjustment process is used to enhance stego-image visual quality obtained by simple LSB substitution method. To ensure that the adaptive number k of LSBs remains unchanged after pixel modification, the LSBs number is computed by the high-order bits rather than all the bits of the image pixel value. The theoretical analyses and experiment results show that the proposed method achieves higher embedding capacity and better stegoimage quality compared with some existing LSB methods.

Keywords: Data Hiding, Adaptive Least Significant Bits Substitution, Human Visual System, High Embedding Capacity, Optimal Pixel Adjustment Process.

E. Ferdinandov, K. Dimitrov, A. Dandarov, I. Bakalski [references] [full-text] [Download Citations]
A General Model of the Atmospheric Scattering in the Wavelength Interval 300 - 1100nm

We have presented and developed new theoretic-empirical models of the extinction coefficients of the molecular scattering in the lower, close to the ground troposphere. We have included the indicatrices of backscattering. The models have been presented using general analytical functions valid for the whole wavelength interval 300-1100 nm and for the whole interval of visibility from 0.1 km up to 50 km. The results have been compared in quantity with the model and experimental data of other authors. The modeling of troposphere scattering is necessary for the analysis and design of all optoelectronic free space systems: atmospheric optical communication systems, location systems for atmospheric research (LIDAR), optical radiometric systems.

Keywords: Model, extinction, atmosphere, visibility, lidar.

A. Lahiri [references] [full-text] [Download Citations]
Explicit-Current-Output Quadrature Oscillator Using Second-Generation Current Conveyor Transconductance Amplifier

This paper presents a novel quadrature sinusoidal oscillator using second-generation current conveyor transconductance amplifier as an active building block. The proposed circuit employs only a single second-generation current conveyor transconductance amplifier, four passive components. The proposed circuit offers the advantages of independent control of the condition of oscillation and frequency of oscillation, availability of two explicit quadrature current outputs and two quadrature voltages, use of allgrounded passive elements and low active and passive sensitivities. The workability of the proposed circuit is confirmed by SPICE simulations.

Keywords: Single-element-controlled oscillators (SECOs), singleresistance-controlled oscillators (SRCOs), quadrature oscillators, second-generation current conveyor transconductance amplifier (CCII-TA).

B. Liu, C. Wang, M. Ma, S. Guo [references] [full-text] [Download Citations]
An Ultra-Low-Voltage and Ultra-Low-Power 2.4 GHz LNA Design

In this paper, ultra-low-voltage and ultra-low-power circuit techniques are presented for CMOS RF front-ends. By employing a modified current-reused architecture, the low-noise amplifier (LNA) can operate at a very low supply voltage with microwatt power consumption while maintaining reasonable circuit performance at 2.4 GHz. Using a TSMC 0.18 um CMOS process, from the simulation results, the fully integrated LNA exhibits a gain of 14.4 dB and a noise figure of 1.6 dB at 2.4 GHz, operated at a supply voltage of 0.9 V, the input matching (S11) is –18.1 dB while consumes only 960 μW. example.

Keywords: Low-noise amplifier, low power, low voltage, low noise.

Q. Wan, C. Wang, M. Ma [references] [full-text] [Download Citations]
A Novel 2.4GHz CMOS Up-Conversion Current-Mode Mixer

In this paper, a low-power up-conversion current-mode mixer, designed in the chartered 0.18-μm RFCMOS technology, is proposed to realize the transmitter front-end in the frequency band of 2.4 GHz. The proposed mixer can convert a 10 MHz intermediate frequency (IF) signal to a 2.4 GHz RF signal, with a local oscillator power of 2 dBm at 2.39 GHz. A comparison with conventional voltage-mode up-conversion mixer shows that this mixer has advantages of low voltage, low power consumption and high performance. Simulation results demonstrate that at 2.4 GHz, the circuit provides 6.5 dB of conversion gain and the input-referred third-order intercept point (IIP3) of 15.3 dBm, while drawing only 5.7 mA from a 1.2V supply voltage. The chip area is only 0.7 mm x 0.8 mm.

Keywords: Current-mode mixer, up-conversion mixer, CMOS, high linearity, low power.

J. Horng [references] [full-text] [Download Citations]
High-Order Current-Mode and Transimpedance-Mode Universal Filters with Multiple-Inputs and Two-Outputs Using MOCCIIs

A high-order current-mode and transimpedance-mode universal filter with multiple-inputs and two-outputs based on multiple output second-generation current conveyors (MOCCIIs) is introduced. By choosing the input current terminals appropriately, the current-mode and transimpedance-mode lowpass, bandpass, highpass, notch or allpass filters can be obtained without component matching conditions. The proposed nth order universal filter requires (n+1) MOCCIIs, (n+1) resistors and n grounded capacitors. As examples, the first-order, biquadratic and third-order universal filters are given and compared with previous published works.

Keywords: Current conveyor, high-order filter, current-mode, transimpedance-mode.

M. Hosseinipanah, Q. Wu [references] [full-text] [Download Citations]
Equivalent Circuit Model for Designing of Jerusalem Cross-Based Artificial Magnetic Conductors

This paper introduces an equivalent circuit model to estimate the resonant frequency and reflection phase of Jerusalem cross-based artificial magnetic conductor (JC-AMC) structures for waves normally incident on the structure. The JC-AMC structure is composed of an array of Jerusalem cross-shaped frequency selective surfaces (JC-FSSs) printed on a metal-backed dielectric slab without vias. This approach is based on the coupled microstrip lines and transmission line theories. Analytical expressions for the resonant frequency and reflection phase resulting from our model are thoroughly verified by full-wave simulations for different samples reported in the open literature. A comprehensive parametric study of the design parameters of JC-AMC structure and the influence of these parameters on the reflection phase properties are presented. This model can easily be extended to complex-shaped AMCs.

Keywords: Artificial magnetic conductor, electromagnetic bandgap, high-impedance surface, Jerusalem crosses, equivalent circuit model.

F. Yu, C. Wang [references] [full-text] [Download Citations]
A CPW-Fed Novel Planar Ultra-Wideband Antenna with a Band-Notch Characteristic

A coplanar waveguide (CPW) fed novel planar ultra-wideband antenna with a band-notch characteristic is presented. The proposed antenna consists of a rectangular metal radiation patch and a tapered arc-shaped ground plane. To achieve ultra wideband, three modifications are introduced, the first one is to remove a 90-degree fan angle on the upper corners of the patch, the second one is to shape the bottom of the patch into an arc, and the third modification is to remove a small fan angle on each side of the ground plane near the feeding line. Simulation results show that the proposed antenna operates over 3.0 to 23 GHz for VSWR < 2. By embedding a C-shaped slot in the radiating patch, a frequency band notch between the bandwidth of 5 to 6 GHz for Wireless LAN (WLAN) will be obtained. All simulations in this work were carried out by using the electromagnetic software Ansoft HFSS 11. Compared with the recently proposed antennas, this antenna has advantages in wide bandwidth, good band-notch characteristic, compact in size and easy design. Details of the proposed antenna are presented, and simulated results show that the antenna has stable radiation patterns and good gain flatness over its whole frequency band.

Keywords: Keywords Coplanar waveguide (CPW), ultra wideband (UWB), planar UWB antenna, C-shaped slot, band-notched characteristic.

V. Ricny [references] [full-text] [Download Citations]
Maximum Available Accuracy of FM-CW Radars

This article deals with the principles and above all with the maximum available measuring accuracy analyse of FM-CW (Frequency Modulated Continuous Wave) radars, which are usually employed for distance and velocity measurements of moving objects in road traffic, as well as air traffic and in other applications. These radars often form an important part of the active safety equipment of high-end cars – the so-called anticollision systems. They usually work in the frequency bands of mm waves (24, 35, 77 GHz). Function principles and analyses of factors, that dominantly influence the distance measurement accuracy of these equipments especially in the modulation and demodulation part, are shown in the paper.

Keywords: FM-CW radar, continual wave, frequency modulation, measurement, distance, velocity.

J. Pidanic, V. Schejbal, D. Cermak [references] [full-text] [Download Citations]
Analysis of Periodic Errors for Synthesized-Reference-Wave Holography

Synthesized-reference-wave holographic techniques offer relatively simple and cost-effective measurement of antenna radiation characteristics and reconstruction of complex aperture fields using near-field intensity-pattern measurement. These methods allow utilization of advantages of methods for probe compensations for amplitude and phasing near-field measurements for the planar and cylindrical scanning including accuracy analyses. The paper analyzes periodic errors, which can be created during scanning, using both theoretical results and numerical simulations.

Keywords: Periodic errors, numerical simulations, accuracy analyses, near-field sampling, holography.

J. L. Jimenez-Martin, V. Gonzalez-Posadas, F. J. Arques, L. E. Garcia-Munoz, D. Segovia-Vargas [references] [full-text] [Download Citations]
Dual Band High Efficiency Power Amplifier Based on CRLH Lines

In this paper we propose the use of Composite Right/Left Hand (CRLH) and Extended Composite Right/Left Hand (ECRLH) transmission lines for the design of dual band high efficiency power amplifiers working in CE class. The harmonic termination can be synthesized using the meta-lines is particularly suitable for CE class amplifiers, which have a termination not as sensitive to the third harmonic as F class amplifier. This paper presents the design procedure and the design equations. The nonlinear phase response of a CRLH and ECRLH transmission line has been utilized to design arbitrary dual-band amplifiers.

Keywords: eywords Power Amplifier, Meta-materials, CE class, CRLH, ECRLH, Diplexer, Statistical Sensitivity.

J. Svihlik [references] [full-text] [Download Citations]
Modeling of Scientific Images Using GMM

This paper deals with modeling of scientific and multimedia images in the wavelet domain. Images transformed into wavelet domain have a special shape of probability density function (PDF). Thus wavelet coefficients PDFs are usually modeled using generalized Laplacian PDF model (GLM), which is characterized by two parameters. The wavelet coefficients modeling can be more efficient, while the Gaussian mixture model (GMM) is utilized. GMM model is given by addition of at least two Gaussian PDFs with different standard deviations. The equation system derived by moment method for GMM model parameters estimation will be presented. The equation system was derived for an addition of two GMM models. So it is suitable for advanced denoising systems, where an addition of two GMM random variables is considered (e.g. dark current). This paper presents a continuing of previous work [11], deals with dark current elimination (novel approach) and shows a better way of to modeling light image and dark current.

Keywords: Gaussian mixture model, discrete wavelet transform, moment method, ML method, dark current.

O. Yildiz, A. E. Yilmaz, B. Gokalp [references] [full-text] [Download Citations]
State-of-the-Art System Solutions for Unmanned Underwater Vehicles

Unmanned Underwater Vehicles (UUVs) have gained popularity for the last decades, especially for the purpose of not risking human life in dangerous operations. On the other hand, underwater environment introduces numerous challenges in navigation, control and communication of such vehicles. Certainly, this fact makes the development of these vehicles more interesting and engineering-wise more attractive. In this paper, we first revisit the existing technology and methodology for the solution of aforementioned problems, then we try to come up with a system solution of a generic unmanned underwater vehicles.

Keywords: Unmanned underwater vehicle, autonomous underwater vehicle, navigation, control and guidance, underwater communications, systems engineering, software framework.

R. Dolecek, J. Novak, O. Cerny [references] [full-text] [Download Citations]
Traction Permanent Magnet Synchronous Motor Torque Control with Flux Weakening

The paper deals with analysis of dynamic behavior of a feedback flux weakening control of PMSM traction drive for light vehicles. The PMSM flux weakening is very important for traction drives. Two torque control structures were analyzed - pure feedback control and feedback control with prediction of the field producing current component. The principles, control structures, simulation and experimental results are given.

Keywords: Permanent magnet synchronous motor, traction drive, torque control, magnetic flux weakening, vector control.

J. Novak, R. Dolecek, O. Cerny [references] [full-text] [Download Citations]
EMC Specific Problems of Frequency Converters Used at Interlocking Device

The paper deals with problems of electromagnetic compatibility (EMC) of frequency control drive of electromotive switch actuator of railway switch. The frequency converter with Pulse Width Modulation (PWM) and the output sinus filter are used for feeding of the asynchronous motor of the switch actuator. This drive is operated in an insulated system of feeding voltages. The drive is fed by a frequency converter with an unshielded cable with length up to 1.2 km. The EMC problems occurring at development and operating of the drive are analyzed in this paper. The used solution of these problems and experience with EMC of the given system from real operation are described in this paper as well.

Keywords: EMC, PWM, interlocking device, control system, converter, sinus filter, switch actuator, railway switch.

O. Jane, H. G. Ilk [references] [full-text] [Download Citations]
A Quantitative Study on Optimum Parameters Selection in Adaptive Unsharp Masking Technique for Infrared Images

Infrared image processing has been the focal point of considerable research activity in the last decade mainly because of its wide application areas in security and defense. With the aid of an existing image enhancement technique, we propose an optimum parameters selection procedure which delivers better performance in sharpness and contrast adjustment for the detection of targets in interest in objective quality metrics. Hence, proposed method ensures that the edges of the targets in infrared images are sharper and that the quality of contrast adjustment has its optimum level with minimum error.

Keywords: Adaptive filtering, surveillance applications, image enhancement, Gauss-Newton algorithm, minimum mean square error.

L. Drazan, R. Vrana [references] [full-text] [Download Citations]
Axial Vircator for Electronic Warfare Applications

This paper deals with a high power microwave generator with virtual cathode – vircator in axial release for electronic warfare applications. The classification of directed energy weapons microwave (DEWM) is introduced together with basic block diagrams of a particular class of DEWM. In the paper, methods for designing vircator pulsed power supply, axial vircator structure, measurement methods and experimental results are presented. The vircator in electromagnetic ammunition is powered by magneto-cumulative generator and in weapons for defense of objects (WDO), it is powered by Marx generator. The possible applications of a vircator in the DEWM area are discussed.

Keywords: Electronic warfare, directed energy weapons microwave, high power microwave, magneto-cumulative generator, Marx generator, pulse forming line, vircator.

L. Burita [references] [full-text] [Download Citations]
Multilateral Interoperability Programme

The Multilateral Interoperability Programme (MIP) is a voluntary and independent activity in NATO environment by the participating nations and organizations. The MIP concept is based on data exchange in form of common exchange data model to achieve the international interoperability in command and control information systems (C2IS) of the tactical units. The article describes the basis of the MIP organizations, structure, planning and testing processes. The core of the MIP solution is the Information Exchange Data Model (IEDM). The Czech Armed Forces (CAF) MIP process implementation is mentioned. The MIP example is a part of university education process.

Keywords: Interoperability, Command and Control Information System (C2IS), Multilateral Interoperability Programme (MIP), Joint Consultation Command and Control Information Exchange Data Model (JC3IEDM); data, model, test, CAF, NATO.

M. Varchola, M. Drutarovsky [references] [full-text] [Download Citations]
Embedded Platform for Automatic Testing and Optimizing of FPGA Based Cryptographic True Random Number Generators

This paper deals with an evaluation platform for cryptographic True Random Number Generators (TRNGs) based on the hardware implementation of statistical tests for FPGAs. It was developed in order to provide an automatic tool that helps to speed up the TRNG design process and can provide new insights on the TRNG behavior as it will be shown on a particular example in the paper. It enables to test sufficient statistical properties of various TRNG designs under various working conditions on the fly. Moreover, the tests are suitable to be embedded into cryptographic hardware products in order to recognize TRNG output of weak quality and thus increase its robustness and reliability. Tests are fully compatible with the FIPS 140 standard and are implemented by the VHDL language as an IP-Core for vendor independent FPGAs. A recent Flash based Actel Fusion FPGA was chosen for preliminary experiments. The Actel version of the tests possesses an interface to the Actel’s CoreMP7 softcore processor that is fully compatible with the industry standard ARM7TDMI. Moreover, identical tests suite was implemented to the Xilinx Virtex 2 and 5 in order to compare the performance of the proposed solution with the performance of already published one based on the same FPGAs. It was achieved 25% and 65% greater clock frequency respectively while consuming almost equal resources of the Xilinx FPGAs. On the top of it, the proposed FIPS 140 architecture is capable of processing one random bit per one clock cycle which results in 311.5 Mbps throughput for Virtex 5 FPGA.

Keywords: TRNG, on-chip randomness tests, FIPS 140, FPGA

F. Dvorak, J. Maschke, C. Vlcek [references] [full-text] [Download Citations]
Utilization of Birefringent Fiber as Sensor of Temperature Field Disturbance

The paper deals with utilization of induced birefringence sensitivity to temperature field in birefringent optical fibers. The propagating optical wave and optical fibers are described by means of coherency and Jones matrices, which are decomposed into unitary matrix and spin matrices. The development of polarization caused by temperature field is interpreted on the Poincare sphere by means of MATLAB® environment. The temperature sensitivity of Panda and bow-tie fiber has been measured for circular polarization excitation. Curves of intensity fluctuation caused by the temperature dependence are presented.

Keywords: Induced birefringence, temperature dependence, birefringence sensitivity, beat length, Jones matrix, coherency matrix, spin matrices, Poincare sphere, temperature sensor.

K. Malinka, P. Hanacek, D. Cvrcek [references] [full-text] [Download Citations]
Analyses of Real Email Traffic Properties

In this paper, we perform an empirical analysis of email traffic logs obtained from a large university to better understand its impact on the effectiveness and efficiency of anonymous mix remailers. We analyzed data containing records of almost 790,000 emails sent over a period of forty days – the largest dataset we are aware of. The initial analysis of data is followed by an exploration of how variance in message arrival time and size impact the anonymity and efficiency provided by timed and threshold mixes, respectively. The analysis results are subsequently explored for their possible impact on traffic analysis.

Keywords: SMTP, email traffic, mixing, anonymity, social networks.

V. Bolom, J. Ingerle, P. Sovka [references] [full-text] [Download Citations]
Derivation of Criterion Suitable for Evaluation of Multichannel Noise Reduction Systems for Speech Processing

This paper deals with the theoretical derivation of the Noise Reduction criterion suitable for evaluation of multichannel noise reduction system performance. This criterion is suitable for noise suppression assessment and thus serves as an important step in the development of noise reduction systems. Noise reduction is evaluated in dependence on spatial coherence. The derivations are made for five basic multichannel systems, Delay and sum beamformer, Beamformer with adaptive postprocessing, Generalized sidelobe canceller, Linearly constrained beamformer, and Modified coherence filter.

Keywords: Beamforming, microphone arrays, speech enhancement, noise reduction.

J. Nouza, J. Silovsky [references] [full-text] [Download Citations]
Fast Keyword Spotting in Telephone Speech

In the paper, we present a system designed for detecting keywords in telephone speech. We focus not only on achieving high accuracy but also on very short processing time. The keyword spotting system can run in three modes: a) an off-line mode requiring less than 0.1xRT, b) an on-line mode with minimum (2 s) latency, and c) a repeated spotting mode, in which pre-computed values allow for additional acceleration. Its performance is evaluated on recordings of Czech spontaneous telephone speech using rather large and complex keyword lists.

Keywords: Speech processing, keyword decoder, HLDA transformation. spotting, speech

F. Grezl, J. Cernocky [references] [full-text] [Download Citations]
Audio Surveillance through Known Event Classification

The way of audio surveillance through known event classification is presented introducing simple yet efficient framework. The use of the proposed system for unknown event detection is also suggested and evaluated. Further, a specific audio event is detected with use of audio classification, which helps the detection to focus on a signal of specific behavior. Thus it is shown that the system can be used in several applications.

Keywords: Sound classification, event detection, audio surveillance.

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