2006/3

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    Optimization of Dynamic Range of Cascade Filter Realization
    (Společnost pro radioelektronické inženýrství, 2006-09) Hospodka, Jiri
    This paper deals with a dynamic range optimization procedure for active filters based on the cascade realization. Dynamic characteristics of the cascade filter depend on many factors, mainly on pole-zero pairing, section ordering and gain assignment. Just the procedure for an optimal gain assignment for particular biquadratic sections is discussed in this paper. The input parameters of the procedure are parameters of particular biquads i.e. pole frequency ω0, quality factor Q, eventually zero frequency ωn for elliptic section and the transfer function type of the section. The gain is distributed so that output signal limitation of particular biquads occurs for the same level of the filter input signal. The procedure is versatile - can be used for analog as well as for digital filters with the cascade structure. The presented algorithm is fully universal (does not suppose any simplification). It has been used in Syntfil package for the filter design in the mathematical program Maple.
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    A Self-Complementary 1.2 to 40 GHz Spiral Antenna with Impedance Matching
    (Společnost pro radioelektronické inženýrství, 2006-09) Piksa, Petr; Mazanek, Milos
    This paper describes a design of the Self- Complementary Spiral Antenna (SCSA) which consists of a spiral antenna and a wideband impedance transformer. The spiral antenna and the transformer are designed separately due to computing demands. New knowledge about current distribution on the spiral antenna and influence of higher numbers of wavelength in circumference is presented. The novel transition between feeding and radiating antenna structure are optimized in the frequency range 1.2 to 40 GHz. The meaning of the transition in the paper includes the impedance as well as the geometry transforming of the structure. The antenna is suitable for wideband illuminating of a parabolic reflector due to relatively constant phase center and radiation pattern with frequency.
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    Controlled Random Search Optimization for Linear Antenna Arrays
    (Společnost pro radioelektronické inženýrství, 2006-09) Merad, Lotfi; Bendimerad, Fethi Tarik; Meriah, Sidi Mohammed
    An optimization problem for designing nonuniformly spaced, linear antenna\'s arrays is formulated and solved by means of a controlled random search algorithm. The proposed iterative method aims at a linear array and the optimization of element positions and excitations coefficients by minimizing the side-lobes level and respecting a beam pattern shape. Selected examples are included, which demonstrate the effectiveness and the design flexibility of the proposed method in the framework of the electromagnetic synthesis of linear antenna arrays.
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    Influence of the FEC Channel Coding on Error Rates and Picture Quality in DVB Baseband Transmission
    (Společnost pro radioelektronické inženýrství, 2006-09) Kratochvil, Tomas
    The paper deals with the component analysis of DTV (Digital Television) and DVB (Digital Video Broadcasting) baseband channel coding. Used FEC (Forward Error Correction) error-protection codes principles are shortly outlined and the simulation model applied in Matlab is presented. Results of achieved bit and symbol error rates and corresponding picture quality evaluation analysis are presented, including the evaluation of influence of the channel coding on transmitted RGB images and their noise rates related to MOS (Mean Opinion Score). Conclusion of the paper contains comparison of DVB channel codes efficiency.
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    Image Reconstruction Based on Deterministic and Heuristic Approach
    (Společnost pro radioelektronické inženýrství, 2006-09) Bachorec, Tibor; Dedkova, Jarmila
    The aim of this paper is to provide a survey of the recent development in new algorithms and techniques to solve the electrical impedance tomography (EIT) inverse problem. The EIT problem is nonlinear and ill-posed. The modified Newton-Raphson method with the Tikhonov regularization and the differential evolution algorithm are used to obtain high-quality reconstruction in EIT problems. Numerical results of the reconstruction based on both deterministic and heuristic methods are presented and compared. Finally, we provide recommendations of solutions of still open problems in this field.