Sharif Digital Repository

The construction of a facies model could be employed as a conditional data for any property simulation that results in a more reliable reservoir characterization in further steps. In this study, an Iranian gas reservoir with six wells was studied to determine the 3D reservoir facies model. Fifteen reservoir facies were first detected along one of the wells with detailed core and thin section descriptions. Due to the significant difference between the core and log data resolution, facies were clustered into four major groups regarding the digenetic processes and petrophysical lithofacies properties (permeability and porosity). The lithofacies specification effect on petrophysical properties... 

Channel characterization is an important step in the design of wireless communication systems. While channel sounding procedures are a useful method in determining channel behavior, they also require expensive and time consuming procedures and equipment. Ray tracing has been an important substitute for measurement in deterministic channel modeling and characterization of the wireless channel. Much has been done to improve the precision and efficiency of this method for lower frequency bands (generally below 5 GHz) over the years. Recently, with the worldwide announcement of a broad unlicensed band in the millimeter wave spectrum around 60 GHz, a great amount of attention has been paid to... 

This paper presents nonlinear signal and noise analysis of a wide gate FET mixer. The study is performed using nonlinear sliced modeling. The FET is taken into account as a distributed element and divided into several smaller pieces so that in each slice a lumped model can be applied. Calculation of passive and active elements of each slice is performed using proper scaling approach. For noise analysis, appropriate noise sources are added to the distributed circuit The wide gate FETs have been suggested for high power, wideband and high gain devices such as travelling wave amplifier. The nonlinear application is suggested for a novel device named travelling wave mixer. © 2000 IEEE  

The influence of the loading of the FET electrodes, on signal and noise performances of the device in mixer application is studied. It is shown that exciting the input signal from one end of the gate and extracting the output signal from the opposite ends of the gate can improve the device characteristics, provided that the two remaining ends of the gate and the drain are properly loaded. This structure makes the lines (i.e. the gate and the drain electrodes) to be matched with the loads. Therefore it leads to a travelling wave FET mixer, which is a good candidate for high power mm-wave application. © 2000 IEEE  

A Green's function to describe the time behavior of the locking phases in a circular planar array of mutually coupled microwave oscillators is proposed. Using this Green's function the dynamic behavior of the array can be described for any arbitrary free running frequency of elements of the oscillator array. Beam steering is realized via detuning the edge oscillators of the array from a reference frequency and the beam direction is controlled by the amount of detuning for each oscillator at the edge. Some detuning functions such as sinusoidal, triangular and rectangular ones have been applied and, the resulting array patterns are compared with one another  

Varactor and bipolar junction transistor (BJT) frequency multipliers are a class of non-linear circuits that show parametric instability when the input drive is varied. If parametric oscillations are present in the circuit, output phase noise of the multiplier degrades remarkably in some specific driving levels. Phase noise analysis is performed by the conversion matrix method using generalised nodal analysis. The conversion method predicts the phase noise degradation precisely because it encompasses the effect of the noise sources that are modulated by the large signal drive. The added phase noise of a varactor and a BJT frequency doubler with subharmonic oscillation is calculated and the... 

In this paper, a new formulation based on conversion matrix method is proposed to analyze "near-the-carrier local ocillator (LO) noise" down conversion to IF in microwave mixers. This method could be easily applied to analyze LO noise down conversion in any type of mixer. Practical results of this method have been compared with the envelope method and measurement results. It is shown that despite the conventional AM noise suppression in balanced mixers, the near-the-carrier LO noise suppression does not occur necessarily at the center frequency of hybrid in balanced mixers. AM noise suppression values are predicted precisely. © 2009 IEEE  

In this paper, a new formulation based on conversion matrix method is proposed to analyze near-the-carrier local ocillator (LO) noise down conversion to IF in microwave mixers. This method could be easily applied to analyze LO noise down conversion in any type of mixer. Practical results of this method have been compared with the envelope method and measurement results. It is shown that despite the conventional AM noise suppression in balanced mixers, the near-the-carrier LO noise suppression does not occur necessarily at the center frequency of hybrid in balanced mixers. AM noise suppression values are predicted precisely. © 2006 IEEE  

During recent years, Shape Memory Alloys (SMAs) have been effectively used to control the seismic response of structural systems. Recovering the residual strains upon unloading (super-elasticity) or by heating (shape memory effect) is the main characteristic of SMA materials. This paper explores the efficiency of a proposed application of steel & SMA bolts in improving the seismic behavior of connections in steel Moment Resisting Frame (MRF) structures. A new semi-rigid, end-plate, beam-column connection is introduced, which is based on parallel application of steel and austenite-phase SMA bolts. A number of 3-D steel MRF structural models with different numbers of stories and mass... 

Arrays of N weakly coupled oscillators are considered in different configurations. The locking bandwidth for these arrays is defined statistically. Various factors affecting the locking bandwidth and the effect of the coupling network topology on locking bandwidth are studied by solving the dynamic equations of the array numerically. The analytical locking bandwidth for two configurations of arrays is computed and the results are compared with the numerical solution of dynamic equations. © The Institution of Engineering and Technology 2008  

Stability has been one of the major issues of time-domain numerical methods used for solving Maxwell equations. This problem takes a more severe form when additional algorithms are introduced to the computation domain (e.g. Absorbing Boundary Conditions-ABCs). There are a number of methods for investigating the stability of a simulation. In this article the problem of stability of ABCs, has been tackled through a control system's state-space point of view. Thus, occurrence of instability in a simulation can be predicted. © 2007 IEEE  

Feed-forward is one of the best methods for linearizing microwave power amplifiers, but due to device tolerance in implementation of the system components, the practical Inter-Modulation Rejection (IMR) value may differ quite much from the theoretical IMR value. One of the methods to improve the practical performance of the system is using the multi-loop configuration. Here we have introduced the multi-loop feedforward systems and we have estimated the practical IMR values of the system using Monte-Carlo analysis. As the analysis shows, although the number of components in a multi-loop system is increased with respect to a simple feed-forward system, but the difference between the practical... 

Phase noise in two mutually coupled oscillators is analyzed by the describing function method, and the after-lock phase noise of the oscillators is calculated in terms of their free-running phase noise. A new phase-noise measurement technique based on inter-injection locking of two similar oscillators is proposed. Experimental results are presented, which confirm the theory. It is shown that in the case of zero phase of coupling coefficient, the system is in the optimum state where the only required parameter for the measurement is the locking bandwidth. In this optimum state, as far as the locking bandwidth is measured correctly, imperfections such as the frequency drift, parameters... 

A traveling wave distributed mixer is studied. It is shown that increasing the drain-source capacitances in a distributed FET mixer simultaneously improves its conversion gain and noise figure. Besides, it is shown that proper loading of input and output elements can improve the device performance. The simulation results are well matched with the measurements and also with the results of the existing certified simulators. © 2002 IEEE  

In an electronic warfare environment, an electronic support system receives signals emitted by different radars. One of the key tasks in an electronic support system is detection of Pulse Repetition Interval Modulation for these signals. In this paper we present a new robust and yet simple method for detection of complex PRI Modulation. Simulation results show that the proposed method is more robust against noise (spurious and missing pulses) and unwanted jitter than previous methods  

Phase noise is one of the most important specifications of microwave oscillators. External factors such as mechanical vibrations increase the phase noise of the oscillator. A novel technique is introduced to reduce vibration-induced phase noise using inter-injection locking of two coupled oscillators. Two similar oscillators with equal free running frequencies are chosen and are subjected to sinusoidal vibration. The mechanical configuration is such that vibration sensitivity vector increases the frequency of one oscillator and decreases the other one's frequency of oscillation. Coupling these two oscillators using inter-injection locking, the common after-lock frequencies of both... 

The conventional delay-line discriminator method for phase noise measurement is modified to achieve better sensitivity. In the proposed technique, to decrease delay-line loss, the under-test oscillator's microwave frequency is down-converted by another oscillator, and delay-line is implemented in the IF range. Full validation of the technique is presented. In adition, we experimentally demonstrate that system sensitivity is considerably improved compared to the conventional method  

An analysis of resonant modes in ladder networks is performed using difference equations. Linear and loop configurations are studied and analytical relations are derived for the mode distributions and resonant frequencies of these networks, having arbitrary elements. Furthermore, it is shown that a) Modes with an exponential distribution along network nodes may exist in some cases and b) The mode distributions in loop networks are independent of network elements. Finally, a simple criterion is obtained for a loop structure to control the spacing between resonant frequencies. © Sharif University of Technology, April 2008  

Properly terminating a transmission line, in order to transfer the maximum available power to the load, is an important issue. The problem, fully analyzed in linear lines, is still considered as a persisting problem in the area of nonlinear transmission lines (NLTLs). In this paper, an accurate analysis is presented which gives a closed-form formula for the matching efficiency of the NLTLs. Using this analysis, optimal resistive terminating load for the NLTLs was extracted. These results will considerably ease the design of all kinds of the NLTL-based systems, such as high-frequency oscillators and ultrashort pulse generators. This consistent analysis also gives the reflection coefficient... 

A new-designed surfactant was prepared with capability of tolerating high saline formation water and real oil reservoir conditions. The specific emulsion behavior of this new chemical was investigated by doing all sets of emulsion stability and emulsion behavior tests in presence of different alkalis. Four types of alkalis (Sodium Hydroxide, Sodium Carbonate, Sodium Metaborate, and Triethanolamine) were mixed with the surfactant and their combined effect on aqueous-oil emulsion behavior was inspected. The experimental results shoine formation water and real oil reservoir conditions. The specific emulsion behavior of this new chemical was investigated by doing all sets of emulsion stability...