2005/4

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    Shielding and Radiation Characteristics of Cylindrical Layered Bianisotropic Structures
    (Společnost pro radioelektronické inženýrství, 2005-12) Vegni, Lucio; Toscano, Alessandro
    In this paper we propose an analytical study in the spectral domain of cylindrical layered structures filled with general bianisotropic media and fed by a 3D electric source. The integrated structure is characterized in terms of transmission matrices leading to an equivalent circuit representation of the whole multilayered structure. Within the framework of this two-port formalism, we present a new contribution to the computation of the Green's function arising in the analysis of multilayered conformal integrated antennas loaded with general bianisotropic materials. We also propose an analytical study of the shielding effectiveness of general bianisotropic materials located in multilayered, cylindrical configuration. The expression of the shielded fields sustained both by plane wave and arbitrary sources is obtained in a closed analytical form. Numerical results are also presented showing effects of electromagnetic parameters on radiation pattern, matching properties and radar cross section of the integrated structure.
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    Radiation Pattern Reconstruction from the Near-Field Amplitude Measurement on Two Planes Using PSO
    (Společnost pro radioelektronické inženýrství, 2005-12) Tkadlec, Roman; Novacek, Zdenek
    The paper presents a new approach to the radiation pattern reconstruction from near-field amplitude only measurement over a two planar scanning surfaces. This new method for antenna pattern reconstruction is based on the global optimization PSO (Particle Swarm Optimization). The paper presents appropriate phaseless measurement requirements and phase retrieval algorithm together with a brief description of the particle swarm optimization method. In order to examine the methodologies developed in this paper, phaseless measurement results for two different antennas are presented and compared to results obtained by a complex measurement (amplitude and phase).
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    Multi-Objective Optimization of Wire Antennas: Genetic Algorithms Versus Particle Swarm Optimization
    (Společnost pro radioelektronické inženýrství, 2005-12) Lukes, Zbynek; Raida, Zbynek
    The paper is aimed to the multi-objective optimization of wire multi-band antennas. Antennas are numerically modeled using time-domain integral-equation method. That way, the designed antennas can be characterized in a wide band of frequencies within a single run of the analysis. Antennas are optimized to reach the prescribed matching, to exhibit the omni-directional constant gain and to have the satisfactory polarization purity. Results of the design are experimentally verified. The multi-objective cost function is minimized by the genetic algorithm and by the particle swarm optimization. Results of the optimization by both the multi-objective methods are in detail compared. The combination of the time domain analysis and global optimization methods for the broadband antenna design and the detailed comparison of the multi-objective particle swarm optimization with the multi-objective genetic algorithm are the original contributions of the paper.
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    Assembly Influence on the Small-Signal Parameters of a Packaged Transistor
    (Společnost pro radioelektronické inženýrství, 2005-12) Sokol, Vratislav; Cerny, Petr; Hoffmann, Karel; Skvor, Zbynek
    A detailed analysis of the assembly influence on the small-signal parameters of a packaged transistor is presented. A new method, based on 3D field simulation and mixed-mode scattering parameters approach is proposed. Differences in scattering parameters caused by assembly change are computed using the new proposed method and compared to the standard method based on admittance matrix. The differences, accuracy, error sources and suitability of both methods are discussed. Results are verified experimentally in microstrip line for two fundamental assembly changes of a transistor in SOT 343 package in frequency range 45 MHz - 18 GHz.
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    New Planar and Volume Versions of a Metamaterial
    (Společnost pro radioelektronické inženýrství, 2005-12) Machac, Jan; Hudlicka, Martin; Buchar, Pavel; Zehenther, Jan
    Some characteristics of materials with negative permittivity and permeability, i.e., with a negative refrative index, known as metamaterials, are presented in this paper. Dispersion characteristics of left-handed parallel strips calculated by different methods are compared with each other. The calculated and measured dispersion and transmission characteristics of a newly proposed left-handed coplanar waveguide and of a novel volume metmaterial are shown. Simple equivalent circuits of both structures are presented together with elements values. The structures exhibit a negative refractive index in a wide frequency band.