No. 1 (2003)
Published:
2003-03-30
ARTICLES FROM THIS ISSUE
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New approach to computer aided design of coupled resonator filters
Abstract
A gradient based optimization technique along with a new definition of cost function is applied to synthesis of coupled resonators filters. The cost function is defined using location of zeros and poles of the filter`s transfer function. The topology of the structure is enforced on each step of optimization and its physical dimensions are used as independent variables.
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Modulator structures for radio-on-fiber applications
Abstract
Traditional electro-optic modulators are not optimized for bandpass applications such as radio-on-fiber delivery systems due to their limited electro-optic response. This paper presents a resonant electrode structure that can be employed in optical modulator designs to enhance the electro-optic response of the modulator over a narrow frequency band, and improve the performance of optical radio systems. A simple model of the structure is developed, and experimental results validating the model and illustrating the effectiveness of the structure are presented.
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A 24 GHz PHEMT-based oscillator
Abstract
We present a systematic nonlinear procedure for designing microwave oscillators utilising a nonlinear PHEMT model, the negative resistance approach and the describing function concept. The procedure is applied in the design of a 24 GHz oscillator, which is then realised in hybrid technology. Measurement results show -6% shift in the frequency but an acceptable agreement in the output power. A detailed analysis shows that the frequency shift arises mainly from inadequate CAD models in the K band, for the microstrip components employed in our design.
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Synthesis method for distributed amplifiers
Abstract
New design method is presented for distributed amplifiers (DA). It is shown that by proper design of the applied transmission lines (TL) between the active devices the image impedance and the cut-off frequency COF of the input or output line of the DA can be independently tuned. As a consequence, the phase mismatch between the lines of the DA can be adjusted independently from the termination conditions and from the capacitances of the applied transistor and thus flat gain characteristic can be achieved. The method is well applicable for nearly unilateral devices like HBTs [1] and yields the highest gain-bandwidth product.
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Reliability and low-frequency noise measurements of InGaAsP MQW buried-heterostructure lasers
Abstract
A laser diode reliability test based on the measurements of the low-frequency optical and electrical noise, and their correlation factor changes during short-time ageing is presented. The noise characteristics reveal obvious differences between the stable and unreliable lasers operated near the threshold region. An excessive Lorentzian type noise with negative correlation factor at the threshold could be one of the criteria for identifying unreliable lasers. The behavior of unreliable lasers during ageing could be explained by migration of point recombination centres at the interface of an active layer, and by the formation of defect clusters.
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Optical control of semiconductor synchronized microwave oscillators in the power suppression mode
Abstract
The influence of optical radiation on the performance of the synchronized microwave Gunn-diode oscillator in the coherent signals subtraction mode has been described theoretically and investigated experimentally. The high sensitivity of the oscillator characteristics to the change of the optical intensity affecting the semiconductor diode structure has been shown. It is suggested to use this mode for the creation of optoelectronic microwave systems with the controlled amplitude and phase of the output signal and for the high-accuracy indication of optical radiation.
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Vertical cavity surface emitting lasers in radio over fiber applications
Abstract
Theoretical and experimental study of using direct modulated vertical cavity surface emitting lasers in radio over fiber applications is presented. The nonlinear distortion and signal to noise ratio are investigated and evaluated in case of short-range multi-carrier transmission. Nonlinear characterization and comparison of the different kind of semiconductor lasers are also presented.
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Evaluation of near field of the GSM base station antennas in urban environment
Abstract
A simple and efficient method for evaluation of near field of the GSM base station antennas in urban environment is presented in this paper. The method is based on the replacement of panel antenna with a discrette linear array. Moreover, the geometrical optics approach is used to consider the influence of environment. The approximate results are found to be in excellent agreement with the results obtained by using the method of moments (MoM). Presented method can be successfully used for fast evaluation of exposure to electromagnetic fields emitted by the GSM base station antennas in urban environment.
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Integration of home digital network and Bluetooth wireless communication system
Abstract
The paper presents new method of integration home digital network with Bluetooth wireless communication system. In this new application Bluetooth is used as one of the main ways of communication and information exchange between elements of the system for integrated, centralized control of the digital devices in the multimedia home platform. Bluetooth enables communication between multimedia gateway with the HTTP server inside and personal communication assistants (PCA), special kind of the remote control. The aim of the system is centralization of services in the multimedia gateway and integration of different services using only one control device.
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Applying the relational modelling and knowledge-based techniques to the emitter database design
Abstract
The appropriate emitter database is one of the most important elements in the present electronic intelligence (ELINT) system. This paper provides an overview of the relational modelling, which is used to construct the emitter database for current ELINT systems. The method described, delivers the entities` relational diagram that is independent from the manner of the data storage in further process of implementation. This approach ensures the integrity of the measured data. The process of final emitter identification is based on ``the knowledge-based approach`` which was implemented during the process of constructing the database.
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Optimal site and antenna location for UMTS - output results of 3G network simulation software
Abstract
The paper presents output results of 3G network simulation software in the area of optimal site location as well as finding optimal values of antenna tilt. The loss of capacity is shown for a wide range of tilts and different antenna directions. Nonuniform distribution of base stations has been also included in the simulation scenarios influencing system performance. All of the described parameters are especially significant to CDMA systems network planning.
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FDTD modeling and experimental verification of electromagnetic power dissipated in domestic microwave ovens
Abstract
The FDTD (Finite Difference Time Domain) method has proven to be effective in modeling high-frequency electromagnetic problems in telecommunications industry. Recently it has been successfully applied in microwave power engineering. In order to accurately model scenarios typical in this field one has to deal with the movement of objects placed inside cavities. This paper describes a~simple algorithm that makes it possible to take into account object rotation - important in simulations of domestic microwave ovens. Results of example simulations are presented and an experimental verification of the simulation tool is performed.
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Theory of scattering by an array of lossy dielectric, ferrite and conducting cylinders
Abstract
Theory of scattering by lossy dielectric, ferrite and/or conducting cylinders is investigated using a combination of an iterative scattering procedure and the orthogonal expansion method. The addition theorems for vector cylindrical harmonics, which transform harmonics from one coordinate system to another, are presented.
