2007/2

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Optimization of Transient Response Radiation of Printed Ultra Wideband Dipole Antennas (Using Particle Swarm Optimization Method)
(Společnost pro radioelektronické inženýrství, 2007-06) Cerny, Petr; Mazanek, Milos
In case of particular ultra wideband applications (i.e. radar, positioning, etc.), it is crucial to know the transient responses of antennas. In the first part of the paper, the optimization process searches for the dipole shape that accomplishes two required parameters i.e. a good matching and a minimal distortion. The particle swarm optimization method was used in the process of the dipole shape optimization. As a result, the optimized ultra wideband dipole is perfectly matched. Moreover, it minimally distorts the applied signal. The second part of the paper discusses the influence of the feeding circuit on radiating parameters and on the dipole antenna matching.
Total Differential Errors in One-Port Network Analyzer Measurements with Application to Antenna Impedance
(Společnost pro radioelektronické inženýrství, 2007-06) Yannopoulou, Nikolitsa; Zimourtopoulos, Petros
The objective was to study uncertainty in antenna input impedance resulting from full one-port Vector Network Analyzer (VNA) measurements. The VNA process equation in the reflection coefficient ρ of a load, its measurement m and three errors Es, determinable from three standard loads and their measurements, was considered. Differentials were selected to represent measurement inaccuracies and load uncertainties (Differential Errors). The differential operator was applied on the process equation and the total differential error dρ for any unknown load (Device Under Test DUT) was expressed in terms of dEs and dm, without any simplification. Consequently, the differential error of input impedance Z -or any other physical quantity differentiably dependent on ρ- is expressible. Furthermore, to express precisely a comparison relation between complex differential errors, the geometric Differential Error Region and its Differential Error Intervals were defined. Practical results are presented for an indoor UHF ground-plane antenna in contrast with a common 50 Ω DC resistor inside an aluminum box. These two built, unshielded and shielded, DUTs were tested against frequency under different system configurations and measurement considerations. Intermediate results for Es and dEs characterize the measurement system itself. A number of calculations and illustrations demonstrate the application of the method.
Analytical Modeling of Insulated Dipole Applicators for Interstitial Hyperthermia: a Review
(Společnost pro radioelektronické inženýrství, 2007-06) Sagnard, Florence
Microwave hyperthermia appears as an adjuvant technique to heat relatively small tumors in a minimally invasive way. As this technique is based on interstitial antennas, we propose a review of the physical phenomena involved in the radiation of such antennas in a dispersive medium, using the different analytical modeling developed since the 1970\'s. These modeling have been implemented in a freely available software tool, that will allow antenna designers and medical researchers to perform rapid parameter studies to further understand the role of the several parameters involved; this tool will also help the interpretation of results issued from numerical simulations. Simulation results associated with different antenna geometries are presented and compared to results obtained by several authors.
Segmentation Based Image Scanning
(Společnost pro radioelektronické inženýrství, 2007-06) Pracko, Richard; Polec, Jaroslav; Hasenohrlova, Katarina
The submitted paper deals with separate scanning of individual image segments. A new image processing approach based on image segmentation and segment scanning is presented. The resulting individual segments 1-dimensional representation provides higher neighbor pixel similarity than the 1-dimensional representation of the original image. This increased adjacent pixel similarity was achieved even without application of different recursive 2-dimensional scanning methods [4], such as Peano-Hilbert scanning method [1]. The resulting 1-dimensional image representation provides a good base for applying lossless compression methods, such as the entropic coding. The paper contains also results analysis of the traditional method scanned segment pixels and adjacent pixel differences from the entropy point of view. As these results indicate the lossy compression methods could be applicable using this approach as well and might improve the final results as confirmed by simple prediction algorithm results presented in this paper. More complex and sophisticated lossy compression algorithms application will be a part of the future work.
A New 3-D Piecewise-Linear System for Chaos Generation
(Společnost pro radioelektronické inženýrství, 2007-06) Elhadj, Zeraoulia
We propose in this paper a new simple continuous-time piecewise-linear three dimensional system for chaos generation. Nonlinearity in this model is introduced by the characteristic function of the Chua\'s circuit given in [1]. Simulated results of some chaotic attractors are shown and justified numerically via computing the largest Lyapunov exponent. The possibility and the robustness of the circuitry realization is also given and discussed.

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