# June 2006, Volume 15, Number 2

**T. Dostal**
[references] [full-text]

On Canonical Structures of ARC Biquadratic Filters with Single Transconductor

The paper deals with simple canonical structures of the second order ARC filters employing only single transconductor (OTA) and passive components R and C. A systematic design procedure of this circuits based on the given autonomous networks is described. Several appropriate general autonomous circuits are presented and studied.

- CHEN, W.K. The Circuits and Filters Handbook. CRC Press, Florida, 1995.
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- SUN, Y., FIDLER, J. K. Novel OTA-C realizations of biquadratic transfer functions. International Journal of Electronics, 1993, vol. 75, p. 333 -348.
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- DOSTAL, T., CAJKA, J., VRBA, K. Design procedure of oscillators and biquads based on current conveyors. In Proc. of 8th WSEAS International Conference on Circuits. Athens, 2004, p. 487-215.
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Keywords: Analogue circuits, active RC filters, biquads, transconductors

**P. Kutin, M. Kasal**
[references] [full-text]

Novel Optimization Method of Active Frequency Multiplier Utilizing Harmonic Terminating Impedances with DGS

A novel method for the optimization of the active frequency multiplier utilizing the harmonic terminating impedances with the defected ground structures (DGS) has been developed. Furthermore, a new type of the low-pass filter with DGS for the higher harmonic suppression will be reported. Experimental conversion gains (14.52 dB for the doubler, 5.56 dB for the tripler and 0.43 dB for the quadrupler) and real power-added efficiency (32.76 % for the doubler, 10.15 % for the tripler and 1.42 % for the quadrupler) have been attained. To our knowledge, in the considered frequency range, these results represent the best performance reported up to date for the active frequency multipliers utilizing the low-cost BJTs.

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- AHN, D., PARK, J. S., KIM, CH. S., KIM, J., QIAN, Y., ITOH, T. A design of the low-pass filter using the novel microstrip defected ground structure. IEEE Transactions on Microwave Theory and Techniques. 2001, vol. 49, no. 1, p. 86 - 93. ISSN 0018-9480.
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- LIM, J. S., PARK, J. S., LEE, Y. T., AHN, D., NAM, S. Application of defected ground structure in reducing the size of amplifiers. IEEE Microwave and Wireless Components Letters. 2002, vol. 12, no. 7, p. 261 - 263. ISSN 1531-1309.
- PARK, J. S., JUNG, M. S. A novel defected ground structure for an active device mounting and its application to a microwave oscillator. IEEE Microwave and Wireless Components Letters. 2004, vol. 14, no. 5, p. 198 - 200. ISSN 1531-1309.

Keywords: Frequency multiplier, defected ground structure, DGS, harmonic terminating, low-pass filter, optimi-zation

**P. Pomenka, Z. Raida**
[references] [full-text]

Methodology of Neural Design: Applications in Microwave Engineering

In the paper, an original methodology for the automatic creation of neural models of microwave structures is proposed and verified. Following the methodology, neural models of the prescribed accuracy are built within the minimum CPU time.

Validity of the proposed methodology is verified by developing neural models of selected microwave structures. Functionality of neural models is verified in a design - a neural model is joined with a genetic algorithm to find a global minimum of a formulated objective function. The objective function is minimized using different versions of genetic algorithms, and their mutual combinations.

The verified methodology of the automated creation of accurate neural models of microwave structures, and their association with global optimization routines are the most important original features of the paper.

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Keywords: Artificial neural networks, genetic algorithms, metho-dology of developing neural models Bayesian regula-rization, Levenberg-Marquardt algorithm

**P. Hazdra, M. Mazanek**
[references] [full-text]

L-System Tool for Generating Fractal Antenna Structures with Ability to Export into EM Simulators

An L-System (Lindenmayer system) is a scheme primarily developed in the area of the computer science for simulating the development of biological structures. It has also been found very useful for generating the geometry of various fractal antennas. A Matlab environment has been used for both implementing an in-plane L-systems algorithm and for creating appropriate files for widely used EM simulators like the IE3D and the CST Microwave Studio. Finally, the performance of the developed script is demonstrated on two fractal microstrip patch antennas.

- http://en.wikipedia.org/wiki/L-system
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Keywords: Fractal antennas, fractals, L-Systems, EM simulation, microstrip patch antennas

**E. D. L. H. Palmero, Z. Raida, R. L. Ruiz**
[references] [full-text]

Quad-Band U-Slot Antenna for Mobile Applications

In this paper, two different planar quad-band antennas are designed, modeled, fabricated and measured. Subsequently, the antennas are redesigned using an electromagnetic band gap substrate (EBG). Those new planar antennas operate in four frequency bands: 900 MHz, 1 800 MHz (both GSM), 1 900 MHz (USA) and 2 400 to 2 500 MHz (Bluetooth) The antenna has four narrow U-shaped slots etched to the patch. Using software, CST Microwave Studio [1], Zeland IE3D [2], and FEMLAB [3], simulations have been carried out to investigate the antenna\'s performance and characteristics. The antennas designed have been also built and measured to compare the real results with those obtained from the simulations.

- CST Reference Manual. Darmstadt: Computer Simulation Technology, 2005.
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- ABEDIN, M. F., ALI, M. Effects of EBG reflection phase profiles on the input impedance and bandwidth of ultra-thin directional dipoles. IEEE Transactions on Antennas and Propagation. 2005, vol. 53, no. 11, p. 3664-3672.
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- FAN, Y., RAHMAT-SAMII, Y. Reflection phase characterizations of the EBG ground plane for low profile wire antenna applications. IEEE Transactions on Antennas and Propagation. 2003, vol. 51, no. 10, p. 2691-2703.
- DE MAAGT, P., GONZALO, R., VARDAXOGLOU, Y. C., BARACCO, J. M. Electromagnetic bandgap antennas and components for microwave and (sub) millimeter wave applications. IEEE Transactions on Antennas and Propagation. 2003, vol. 51, no. 10, p. 2667 to 2677.
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Keywords: Multi-band planar antennas, perturbation slots, modal analysis, full-wave analysis, GSM, Bluetooth. EBG substrates

**J. Pavlovicova, M. Oravec, J. Polec, M. Kelesi, M. Mokos**
[references] [full-text]

Error Concealment using Neural Networks for Block-Based Image Coding

In this paper, a novel adaptive error concealment (EC) algorithm, which lowers the requirements for channel coding, is proposed. It conceals errors in block-based image coding systems by using neural network. In this proposed algorithm, only the intra-frame information is used for reconstruction of the image with separated damaged blocks. The information of pixels surrounding a damaged block is used to recover the errors using the neural network models. Computer simulation results show that the visual quality and the MSE evaluation of a reconstructed image are significantly improved using the proposed EC algorithm. We propose also a simple non-neural approach for comparison.

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Keywords: Block-based image coding, error concealment, image restoration multilayer perceptron, radial basis function network, mobile radio channels

**J. Mihalik, V. Michalcin**
[references] [full-text]

3D Motion Estimation of Human Head by Using Optical Flow

The paper deals with the new algorithm of estimation of large 3D motion of the human head by using the optical flow and the model Candide. In the algorithm prediction of 3D motion parameters in a feedback loop and with multiple iterations was applied. The prediction of 3D motion parameters does not require creating of the synthesized frames but directly uses the frames of input videosequence. Next the algorithm does not need extracting of feature points inside the frames because they are given by the vertices of the used calibrated model Candide. As achieved experimental results show, the iteration process in prediction of 3D motion parameters increased the accuracy of estimation above all the large 3D motion. Such a way the estimation error is decreased without its accumulation in long videosequence. Finally the experimental results show that for 3 iterations a state of saturation was achieved what means that by next increasing of the number of iterations practically no significant increasing of the accuracy of estimation of 3D motion parameters is occurred.

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Keywords: Optical flow, 3D motion, estimation, prediction, modeling, human head, algorithm

**Z. Smekal**
[references] [full-text]

Difference Equations with Forward and Backward Differences and Their Usage in Digital Signal Processor Algorithms

In the paper the relation is given between linear difference equations with constant coefficients those obtained via the application of forward and backward differences. Relation is also established between input-output difference equations and state-space difference equations, which define the state of inner quantities of a discrete system. In conclusion, the state-space representation of a discrete system is given, which is suitable for implementing a discrete system in the microprocessor and digital signal processor. The resultant solution consists of the response to input signal and the response to non-zero initial conditions.

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Keywords: Forward and backward differences, difference equations, digital signal processor algorithms

**I. Baronak, P. Kvackaj**
[references] [full-text]

Statistical CAC Methods in ATM

Admission control is a very useful tool for a network operator. It enables effective link utilization with QoS guaranty. Without doubts, CAC function will be important part in evolution of next generation networks. The question, how to choose suitable CAC method as admission control, is crucial for effective exploitation of CAC function. In this paper, we compare three statistical CAC methods providing their suitability as control for specific traffic: Method of Effective Bandwidth, Diffusion Approximation Method and Gaussian Approximation Method.

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Keywords: Connection Admission Control, Method of Effective Bandwidth, Diffusion Approximation Method, Gaussian Approximation Method