December 2001, Volume 10, Number 4
For the design of indoor picocellular systems in the frequency band of 1800/2100 MHz, a signal propagation modelling is needed. Empirical and semi-empirical models represent an efficient approach to the coverage prediction. For these models, suitable empirical parameters must be provided. The indoor propagation measurement campaign in the frequency range of 1900 MHz was carried out in several multi-floored buildings in Prague and Brno . For the campaign a special portable measurement system was developed. Based on the measurement results, the model parameters were derived. Optimised parameters are presented for two basic models (empirical and semi-empirical) according to the indoor environment classification. The results are compared to standard models as well. Accuracy and validity of derived models are discussed.
- PECHAC, P., KLEPAL, M. Empirical Models for Indor Propa-gation in CTU Prague Buildings. Radioengineering, April 2000, vol. 9, no. 1, p. 31-36
- PECHAC, P., KLEPAL, M., MAZANEK, M. Indoor Propagation Modelling in Multi-Storey Buildings in Prague. In Proceedings of the Millennium Conference on Antennas & Propagation - AP2000, Davos, April 2000
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- PECHAC, P., NISZNANSKY, M., HUDEC, P. System for 1900 MHz Mobile Measurements Controlled by PDA Computer. In Proceedings of the Workshop CAD & CAE 2000, Praha 2000, p. 16-18
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A microstrip patch antenna that is coupled to a microstripline by an aperture in the intervening ground plane is analyzed by using the method of moments. Integral equation is formulated by considering the exact dyadic Green's function in spectral domain for grounded dielectric slab so that the analysis includes all coupling effects and the radiation and surface wave effects of both substrates. The combination of the reciprocity method analysis and a Galerkin moment method solution seems to be suitable for a number of planar antenna problems, especially when coupling slots in the ground plane are included. Results for antenna input impedance are compared with other authors and verified by experimental results.
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A technical analysis of the coaxial dipole-array excited by periodically distributed slots in common coaxial feeder is presented. The lossy transmission-line theory is applied for determination of the current on all parts of the system. Calculated results support some properties of the system, especially the radiation pattern and the input impedance.
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Wide-band vector measurements of transmission structures formed by solenoids with 2, 4 and 6 turns above ground plane were performed in the frequency band 45 MHz to 18 GHz. Novel equivalent circuits of these structures were designed. The equivalent circuits fit the measured data very well in the frequency band DC to 11 GHz. Comparison with models known up to now are given.
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New circuit component, active resonator, is proposed for use in microwave and millimetrewave circuits. It consists of a common resonator and an amplifier, compensating for losses in the resonator. Properly designed, such an arrangement behaves as a (passive) resonator with dramatically increased quality factor. High quality factors can be achieved even at millimetrewave frequencies, where common resonators suffer from losses due to small skin depths. Viability of the component is experimentally verified at microwave region using a TE01 dielectric resonator and an oscillator.
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Neural networks are electronic systems which can be trained to remember behavior of a modeled structure in given operational points, and which can be used to approximate behavior of the structure out of the training points. These approximation abilities of neural nets are demonstrated on modeling a frequency-selective surface, a microstrip transmission line and a microstrip dipole. Attention is turned to the accuracy and to the efficiency of neural models. The association of neural models and genetic algorithms, which can provide a global design tool, is discussed.
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The paper deals with classification of ground radar targets. A received radar signal backscattered from a ground radar target was digitized and in the form of radar signal matrix utilized for a feature extraction based on Singular Value Decomposition. Furthermore, singular values of a backscattered radar signal matrix, as a target feature, were utilized for Radar Target Classification by multilayer perceptron. In the learning phase of a multilayer perceptron we used the learning target set and in the testing phase the testing target set was used. The learning and testing target sets were created on the basis of real ground radar targets.
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The paper presents the basic information about establishing of the laboratory for Mobile Communications on the Dept. of Radio Electronics, Brno University of Technology. This information allows to experts from the practice to obtain the general notion about the extent of theoretical knowledge and practical experiences of our students in this field. This information can be also useful for the specialists from universities comparing simple their pedagogical activity in this field respecting the activity in another institute.
- HANUS, S. The Education of Wireless and Mobile Communications Problems on Institute of Radio Electronics, Brno University of Technology. In Proceedings of Czech-Slovak Conference MOBILE COMMUNICATIONS. Bratislava 2000
- HANUS, S. The Laboratory of Wireless and Mobile Communications on Institute of Radio Electronics, FEECS, Brno University of Technology. In Proceedings of the 11th International Czech-Slovak Scientific Conference RADIOELEKTRONIKA 2001. Brno 2001, p. 306-309. ISBN: 80-214-1861-3