Compact amplifier integration in square patch antenna

A packaged microwave bipolar transistor has been integrated directly onto a rectangular microstrip patch to obtain extra power gain and to reduce power losses. The radiating element geometry has been modified to incorporate the active devices. This active antenna uses a small number of components and takes the same place as a passive antenna. An extra gain of 8 dB is obtained at 1.68 GHz.<>     

Automatic mesh generation using the symmetric axis transformationof polygonal domains

An automatic method for generating finite element meshes for multiply connected planar domains with polygonal boundaries (i.e. planar polygons with polygonal holes) is described. The symmetric axis transform is used to obtain a planar graph that partitions the given domain. This transformation may introduce edges in the graph that are too long or too short for generating good meshes. A silver processing algorithm, which transforms the graph into another graph devoid of such edges, is presented. Finally, additional modes are placed on the edges of the graph to obtain a triangulation, and this process is applied iteratively, yielding the final mesh. The method automatically increases the mesh density in regions of rapid change in shape and allows both global and local control of the mesh density. The method also admits the imposition of node compatibility constraints along domain boundaries, thus making the method suitable for meshing planar cell complexes (i.e multiple polygonal domains with shared boundaries in two-dimensional space) and for generating boundary elements for polyhedra in three-dimensional space     

Reliability analysis of hierarchical computer-based systems subject to common-cause failures

The results from reliability modeling and analysis are key contributors to design and tuning activities for computer-based systems. Each architecture style, however, poses different challenges for which analytical approaches must be developed or modified. The challenge we address in this paper is the reliability analysis of hierarchical computer-based systems (HS) with common-cause failures (CCF). The dependencies among components introduced by CCF complicate the reliability analysis of HS, especially when components affected by a common cause exist on different hierarchical levels. We propose an efficient decomposition and aggregation (EDA) approach for incorporating CCF into the reliability evaluation of HS. Our approach is to decompose an original HS reliability analysis problem with CCF into a number of reduced reliability problems freed from the CCF concerns. The approach is represented in a dynamic fault tree by a proposed CCF gate modeled after the functional dependency gate. We present the basics of the EDA approach by working through a hypothetical analysis of a HS subject to CCF and show how it can be extended to an analysis of a hierarchical phased-mission system subject to different CCF depending on mission phases.     

Dependability analysis of systems with on-demand and active failuremodes, using dynamic fault trees

Safety systems and protection systems can experience two phases of operation (standby and active); an accurate dependability analysis must combine an analysis of both phases. The standby mode can last for a long time, during which the safety system is periodically tested and maintained. Once a demand occurs, the safety system must operate successfully for the length of demand. The failure characteristics of the system are different in the two phases, and the system can fail in two ways: (1) it can fail to start (fail on-demand), or (2) it can fail while in active mode. Failure on demand requires an availability analysis of components (typically electromechanical components) which are required to start or support the safety system. These support components are usually maintained periodically while not in active use. Active failure refers to the failure while running (once started) of the active components of the safety system. These active components can be fault tolerant and use spares or other forms of redundancy, but are not maintainable while in use. The approach, in this paper, automatically combines the "availability analysis of the system in standby mode" with the "reliability analysis of the system in its active mode." The general approach uses an availability analysis of the standby phase to determine the initial state probabilities for a Markov model of the demand phase. A detailed method is presented in terms of a dynamic fault-tree model. A new "dynamic fault-tree construct" captures the dependency of the demand-components on the support systems, which are required to detect the demand or to start the demand system. The method is discussed using a single example sprinkler system and then applied to a more complete system taken from the off-shore industry     

Effets de propagation et de brouillage dans les interconnexions de circuits hybrides

The authors present results of modelling and time domain analysis for the interconnecting lines of hybrid circuits. The quasi tem approximation used in our analysis is justified by an electromagnetic study based on spectral domain method. So, we can use the transmission line concept for the time domain analysis. They present the theory of a simulator for the study of resistive coupled lines mounted in cascade. The effects of mismatching, point discontinuities and losses on signal distortions are discussed in the case of one transmission line. For a set of coupled lines, we clarify the parasiting effects between adjacent lines. We show that a screen-line can reduce these effects if some design rules are respected.     

A broadband highly linear BiCMOS mixer for direct conversion applications

A highly linear BiCMOS double balanced mixer for direct conversion applications is described and optimized. Based on the combination of active and resistive concepts, and modeled as a variable feedback amplifier, it achieves a high linearity and a good conversion gain. The performances achieved are; a conversion gain up to 12 dB, an output P/sub -1 dB/ of -5 dBm, and a high linearity, with an OIP3 of about +23 dBm and an OIP2 not less than +54 dBm, while requiring a local oscillator power no more than +4 dBm. As it covers a broadband RF spectrum, it can be used for receiving all communication networks located from 0.9 GHz until 2.2 GHz. When active, it drains 6 mA from 3.6 V.     

Microstrip antennas printed on lithium niobate substrate

The measured and calculated characteristics of rectangular microstrip antennas printed on lithium niobate substrate are presented. The effect of the substrate cutting on the resonant frequency and the input impedance of these antennas is also studied     

Parametric studies of DD3R particles seeding on the modified surface of α-alumina support and synthesis of DD3R zeolite membrane

The effects of suspension concentration, number of coating stages and dipping time on seeding quality of DD3R particles on the ceramic supports were investigated. The supports were immersed in aqueous suspensions (0.1, 0.2 and 0.3?wt. %) of the DD3R seeds for three different dipping times 30, 90 and 240?s with different stages of 1, 2 and 3. The SEM analysis was used to study the quality of the seeded layers. The optimized seeding conditions of 0.2?wt. % suspension concentration, 2 number of coating stages and 30?s for dipping time leaded to obtain a uniform seeded layer with monolayer structure. The DD3R zeolite membrane was synthesized via hydrothermal method under the optimized seeding conditions. The XRD and SEM analyses confirmed the synthesis of DD3R membrane with proper quality. The single gas permeation results showed a good performance in the separation of CO₂ from CH₄.     

A new discrete wavelet transform appropriate for hardware implementation

A new method for computation of discrete wavelet transform (DWT) is introduced. The impulse response of the FIR filter, as the main block in filter bank (FB) method, is realized such that orthonormal wavelet transform is achieved without using any multiplier as the most challenging part of the FIR filters. The occupied slices and LUTs in the FPGA realization of the proposed wavelet in comparison with those of Daubechies wavelet are decreased by %50 and %56, respectively.