2010/3

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    Fine-Tuning on the Effective Patch Radius Expression of the Circular Microstrip Patch Antennas
    (Společnost pro radioelektronické inženýrství, 2010-09) Yilmaz, Asim Egemen
    In this study, the effective patch radius expression for the circular microstrip antennas is improved by means of several manipulations. Departing from previously proposed equations in the literature, one of the most accurate equations is picked up, and this equation is fine-tuned by means of Particle Swarm Optimization technique. Throughout the study, impacts of other parameters (such as the definition of the fitness/objective function, the degree-of-freedom in the proposed effective patch radius expression, the number of measured resonant frequency values) are observed in a controlled manner. Finally, about 3% additional improvement is achieved over a very accurate formula, which was proposed earlier.
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    Ternary Chaotic Pulse Compression Sequences
    (Společnost pro radioelektronické inženýrství, 2010-09) Seventline, J. B.; Rani, D. Elizabath; Rajeswari, K. Raja
    In this paper method available for generating ternary sequences is discussed. These sequences are useful in many applications but specifically in synchronization of block codes and pulse compression in radar. The ternary sequences are derived from chaotic maps. It is feasible to achieve simultaneously superior performances in detection range and range resolution using the proposed ternary sequences. The properties of these sequences like autocorrelation function, Peak Side Lobe Ratio (PSLR), ambiguity diagram and performance under AWGN noise background has been studied. The generation of these sequences is much simpler, and the available number of sequences is virtually infinite and not limited by the length of the sequence.
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    BER Performance Simulation of Generalized MC DS-CDMA System with Time-Limited Blackman Chip Waveform
    (Společnost pro radioelektronické inženýrství, 2010-09) Develi, Ibrahim; Kockaya, Kenan
    Multiple access interference encountered in multicarrier direct sequence-code division multiple access (MC DS-CDMA) is the most important difficulty that depends mainly on the correlation properties of the spreading sequences as well as the shape of the chip waveforms employed. In this paper, bit error rate (BER) performance of the generalized MC DS-CDMA system that employs time-limited Blackman chip waveform is presented for Nakagami-m fading channels. Simulation results show that the use of Blackman chip waveform can improve the BER performance of the generalized MC DS-CDMA system, as compared to the performances achieved by using timelimited chip waveforms in the literature.
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    Probabilistic Model for Free-Space Optical Links Under Continental Fog Conditions
    (Společnost pro radioelektronické inženýrství, 2010-09) Khan, Muhammad Saeed; Awan, Muhammad Saleem; Muhammad, Sajid Sheikh; Faisal, Muhammad; Marzuki; Nadeem, Farukh; Leitgeb, Erich
    The error characteristics of a free-space optical (FSO) channel are significantly different from the fiber based optical links and thus require a deep physical understanding of the propagation channel. In particular different fog conditions greatly influence the optical transmissions and thus a channel model is required to estimate the detrimental fog effects. In this paper we shall present the probabilistic model for radiation fog from the measured data over a 80 m FSO link installed at Graz, Austria. The fog events are classified into thick fog, moderate fog, light fog and general fog based on the international code of visibility range. We applied some probability distribution functions (PDFs) such as Kumaraswamy, Johnson SB and Logistic distribution, to the actual measured optical attenuations. The performance of each distribution is evaluated by Q-Q and P-P plots. It is found that Kumaraswamy distribution is the best fit for general fog, while Logistic distribution is the optimum choice for thick fog. On the other hand, Johnson SB distribution best fits the moderate and light fog related measured attenuation data. The difference in these probabilistic models and the resultant variation in the received signal strength under different fog types needs to be considered in designing an efficient FSO system.
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    A Novel Current-Mode Full-Wave Rectifier Based on One CDTA and Two Diodes
    (Společnost pro radioelektronické inženýrství, 2010-09) Khateb, Fabian; Vavra, Jiri; Biolek, Dalibor
    Precision rectifiers are important building blocks for analog signal processing. The traditional approach based on diodes and operational amplifiers (OpAmps) exhibits undesirable effects caused by limited OpAmp slew rate and diode commutations. In the paper, a full-wave rectifier based on one CDTA and two Schottky diodes is presented. The PSpice simulation results are included.