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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

An Analysis of a Fast Carrier Recovery System for TDMA

Weaver, Francis Carl 11 1900 (has links)
<p>Phase-locked loops occasionally exhibit prolonged phase transients and are therefore not suitable for carrier recovery applications in time division multiple access (TDMA) systems. Instead, designers have, in several cases, used a single-tuned high Q filter in combination with an automatic frequency control. A non-linear differential equation model for such a system, called a "frequency locked loop" (FLL) is solved by computer to obtain the transient responses. The solutions obtained indicate that the FLL has fast and reliable carrier phase acquisition time compared to a phase-locked loop (PLL). Also, since the non-linear responses agree well with linear model responses, an equation based on the linear model is developed to determine worst-case acquisition time. It is shown that a limiter preceeding the single-tuned tank does not directly affect acquisition performance and will improve noise performance of the FLL. With a limiter, the FLL block diagram is equivalent to an FM feedback demodulator (FMFB) on which there is a large amount of existing literature. Using results from the literature, it is demonstrated how the FMFB will perform in the presence of Gaussian noise. Finally, a design procedure is recommended which takes into account the tradeoff between noise performance and acquisition/tracking ability and attempts to minimize the acquisition time for a given level of Gaussian noise.</p> / Master of Engineering (ME)
52

Processing of ELT Signals for Search and Rescue Satellite Aided Tracking (SARSAT) using the MEM and FFT

Premji, Al-Nasir 03 1900 (has links)
<p>The proposed methods of search and rescue (SAR) of mobile platforms use low altitude polar orbiting satellites to detect signals emanating from emergency locator transmitter (ELT) systems on board the distress platform. The uplink transmission receives a doppler shift due to the radial velocity of the satellite. Extracting the doppler from the signal is necessary for calculating the position of the ELT system. These ELT units were originally designed for reception by ordinary hand held receivers and detection by the human ear. For this reason the transmitters employ a distinct type of modulation often referred to as a chirp. Detection and estimation of the doppler by signal processing is complicated by this swept modulation. This dissertation compares two methods of spectral estimation, namely, Fourier analysis (in the form of an FFT algorithm) and the maximum entropy method (MEM) for application to ELT signals. The signals to be processed are divided into two categories, single and multiple signals. Multiple signal processing is necessary when two or more ELT systems are transmitting simultaneously and the time separation between transmissions is small enough to cause overlapping of signals in time. Results indicate that the enhanced detection capability by using the MEM offers a significant improvement in processing signals from an ELT.</p> / Master of Engineering (ME)
53

Properties and Applications of the Metal-Insulator-Semiconductor (MIS) Tunnel Diode

Green, Andrew Martin 06 1900 (has links)
<p>This work describes a theoretical and experimental investigation into the electrical properties and possible device applications of the three layer Metal-Insulator-Semiconductor (MIS) structure when the insulating layer is very thin (<60A). Under these conditions, current can flow between the metal and the semiconductor by quantum mechanical tunneling processes. This work is limited to the case where the semiconductor is not degenerately doped.</p> <p>To aid in the discussion of the properties of this structure, its electrical behaviour is simulated by describing the transport processes through the semiconductor and the insulator regions mathematically and solving the resulting system of mathematical equation numerically. Solutions for both the AC and DC properties of the structure are obtained in this way. Using these solutions as a guideline, a general theoretical framework is established which allows the device properties to be predicted when parameters such as the work function of the metal contact, the insulator thickness, the properties of surface states at the insulator-semiconductor (IS) interface, the device temperature, and the dopant type in the semiconductor are varied. Particular importance is placed upon the charge conditions in the semiconductor at the IS interface under zero bias conditions. Depending upon whether this region is strongly inverted, depleted, or accumulated, the dominant component of the diode current tends to flow between the metal and the minority carrier energy band, surface state levels, and the majority carrier energy band in the semiconductor respectively. Correspondingly, the devices are classified as minority carrier, surface state, and majority carrier diodes. In addition to this classification, a distinction between "equilibrium" and "non-equilibrium" devices is made. In the former, the insulator layer is thick and the device currents small while in the latter, this layer is thinner and the enhanced current flows cause the semiconductor to depart significantly from thermal equilibrium. Experimental measurements upon the metal-silicon dioxide-silicon system are used to demonstrate the validity of this theory and also demonstrate the utility of the classification scheme described.</p> <p>Non-equilibrium diodes are of particular interest because of their possible device applications. Majority carrier non-equilibrium devices exhibit current multiplication properties which are discussed theoretically and measured experimentally. These make the devices of interest in transistor structures and in such applications as photo-diodes with internal multiplication properties. Minority carrier non-equilibrium devices are shown both theoretically and experimentally to possess properties similar to p-n junction diodes under reverse and small to moderate forward bias. Since they are considerably simpler to fabricate, they have possible application as replacing junction devices in a number of applications such as those as injecting contacts, photo-diodes, or members of photo-diode arrays. One particularly promising application is to direct energy conversion using the electron-or photo-voltaic effect. For an energy conversion situation using the radioisotope Pm147 as the primary energy source it is demonstrated that the predicted higher conversion efficiency of the MIS tunnel diode compared to the p-n junction diode can be experimentally realized.</p> / Doctor of Philosophy (PhD)
54

An Investigation into the Electrical and Radiation Damage Properties of Nitrogen Implanted Silicon, Germanium and Silicon Carbide

Mitchell, Blair James 09 1900 (has links)
<p>The radiation damage and electrical properties of nitrogen implanted silicon, germanium and silicon cardine have been investigated. The object of this investigation has been to relate the damage annealing properties of the implanted semiconductor to the observed electrical behaviour, in an attempt to understand the role of nitrogen in these materials.</p> <p>The study has shown that donor behaviour can be obtained in nitrogen implanted silicon. Capacitance-voltage and Hall effect measurements performed on the implanted layer have indicated that less than 1% of the implanted nitrogen has become electrically active, following anneals in the 700-900ºC range. The ionization energy of nitrogen in silicon has been found by low temperature Hall measurements to be 0.017 ± 0.002 eV. This result has been shown to be independent of the annealing time and the implantation temperature. For doses above ~6 x 10¹4 N/cm², donor results are no longer observed and the damage results have shown that the silicon crystal has no recrystallized well. The results of the above measurements, together with the characteristics of nitrogen implanted diodes and the results of a damage study of nitrogen implanted silicon are presented, and the role of nitrogen in silicon is discussed.</p> <p>The results of electrical and lattice location measurements on nitrogen implanted germanium have shown that nitrogen does not become a donor in germanium. The lattice location measurements have used the 14N(d,α)¹²C nuclear reaction, and have shown that the implanted nitrogen atoms are on interstitial lattice positions. The results of damage measurements obtained by backscattering techniques, together with the electrical and lattice location results are presented.</p> <p>This study has shown that nitrogen implanted silicon carbide exhibits donor behaviour following a high temperature anneal. This result was deduced from the properties of nitrogen implanted silicon carbide diodes and from lattice location measurements performed with the 15N(p,α)¹²C nuclear reaction. These lattice location measurements have shown that approximately 50% of the implanted nitrogen atoms are on the substitutional lattice sites, following an anneal at 1450ºC. This is in excellent agreement with the value of 50% previously reported by other authors as deduced from electrical measurements. Although some problems with the annealing of heavily doped silicon carbide remain to be solved, this study has shown that ion implantation promises to be a useful technique for doping this material.</p> / Doctor of Philosophy (PhD)
55

Convergence Acceleration in Numerical Methods

Kinsner, Witold 03 1900 (has links)
<p>The purpose of this thesis is to present a unified treatment of numerical solutions to the elliptic partial differential equations, particularly the Laplace, Poisson, and Helmholtz equations, in homogeneous and inhomogeneous isotropic media in electrostatic, magnetostatic, and electromagnetic field problems, with particular attention given to iterative solutions. Another objective is to design a family of methods for accelerating the convergence of these solutions. The concept of the convergence acceleration is generalized to deterministic and stochastic vector sequences. Several hybrid methods, combining the finite difference and finite element approaches, are proposed. The methods have been tested either by test examples or by practical solutions to field problems.</p> / Doctor of Philosophy (PhD)
56

Radar System Studies Using Simulation Techniques

Thorsteinson, Magnus Carl 11 1900 (has links)
<p>Pulse-compression is a technique used in radar to transmit a long pulse while retaining the range resolution of a short pulse. The echo from the target is compressed in the matched filter of the radar receiver and the range resolution becomes equal to the width of the central peak of the autocorrelation function of the transmitted signal. A range tracking loop and a range surveillance moving target indicator (MTI) radar using pulse-compression techniques are studied in this thesis. The antenna of these systems is assumed to point along a constant azimuth to simplify the radar surroundings so that the nonlinear aspects of the circuits may be investigated.</p> <p>In a range tracking loop the nonlinearity arises in the delay error feedback process, while in an MTI radar it arises through the limited dynamic range of the circuits used. This thesis presents a computer simulation study of these nonlinear radar systems using Monte Carlo techniques. The computer used in the study is of an interactive kind with oscilloscope display.</p> <p>A new range tracking loop referred to as the decision-directed delay-lock loop has been developed using the fast Fourier transform (FFT) for cross-correlation with a stored replica of the transmitted signal. The loop uses all the lagged products of the FFT cross-correlation output, ans is shown to have a wide dynamic range for large steps of input delay. Using signals already available in the loop, additional features such as automatic feedback gain control and a mechanism for detection of unlocking are built into the loop.</p> <p>The MTI pulse-compression radar has been investigated to determined the effect of a linear-limiting intermediate frequency (IF) amplifier on the signal-to-noise ratio (SNR) at the MTI output. For this study the FFT was used for the purpose of matched filtering and for generating various types of coherent clutter. It has been shown that large SNR losses due to the time-varying effective gain of the clutter-captured limiter may occur at some ranges with particular types of clutter spatial distributions.</p> / Doctor of Philosophy (PhD)
57

Ion Beam Mixing and Thermoelectric Characteristics of Bi-Sb Thin Film Alloys

Ibrahim, Mahmoud Ahmad 08 1900 (has links)
<p>This thesis is concerned with investigating the production of thin film Bi-Sb alloys by ion beam mixing. Samples were composed of a thin Sb film sandwiched between two Bi layers; the thicknesses of the films were varied to produce composition range from 0 to ~45% Sb. The overall thickness was about 55 nm.</p> <p>Analysis of the films by Rutherford Backscattering Spectrometry (RBS) and Auger Electron Spectroscopy (AES) indicated that ion beam mixing can produce uniform Bi-Sb alloys with doses of about 2.8X10¹⁵ cmˉ² of 80 KeV Ar⁺ at room temperature. The results of Electron Microscopy showed a grain growth due to ion bombardment.</p> <p>The mixing was characterized by the increase in the full width at half maximum (FWHM) of the Sb signal in the RBS spectra. It was measured as a function of ion dose, dose rate, mass, and energy. The dependence of mixing on the temperature was also investigated. A square-root dependence of mixing on the dose confirmed a diffusion like mixing process. The rate of mixing per ion dose was found to increase with the elastic energy deposited at the Bi/Sb interface. The mixing is temperature independent in the range of ~40 to ~266 K, i.e., collision cascade mixing dominates. An effective diffusion coefficient, D*, of about 4.9X10ˉ²⁸cm⁴/ion was determined. At temperatures higher than ~266 K, the mixing increases with the temperature. This suggests that a radiation enhanced diffusion mechanism is the dominant mixing process. An effective diffusion coefficient of ~1.7X10ˉ²⁷cm⁴/ion at room temperature was calculated: an activation energy of ~0.15 eV was found.</p> <p>Thermoelectric characteristics of the alloys were investigated by measuring the thermal voltage, V₃, as a function of the temperature, T, in the range 300-500 K, for alloys with various composition. The thermal voltage was found to have a linear dependence on temperature. The thermoelectric power, dV₃/dT, reaches a maximum of about 70 μV/deg, for Bi₈₇Sb₁₃. The dependence of the thermoelectric power on Sb concentration agrees with the model put forward to explain the transport properties of bulk Bi-Sb alloys. An empirical model has been proposed to relate the state of mixing with the measured thermoelectric power.</p> / Doctor of Philosophy (PhD)
58

Sequence Based Receivers for Bandlimited Nonlinear Channels

Dubey, Kishore Vimal 06 1900 (has links)
<p>This thesis examines receiver structures based on maximum likelihood sequence estimation (MLSE) for receiving quaternary phase-shift-keyed (QPSK) signals over bandlimited, non-linear satellite channels, in the presence of additive down link gaussian noise. Two satellite channel models are considered. In the first channel model, the effects of intersymbol interference caused by filtering followed by AM/AM and AM/PM conversions are taken into account while the second channel model includes a post-nonlinearity filter.</p> <p>An explicit expression for the output of the bandpass nonlinearity (BPNL) for a QPSK signal is obtained in terms of an inphase (1)-quadrature (Q) path memory parameter Pk. The computation of the output of the BPNL requires a knowledge of its transfer characteristic. The transfer characteristics may be specified either analytically or through experimental measurements.</p> <p>An optimum MLSE receiver structure for bandlimited, non-linear satellite channel is derived and its performance evaluated using computer simulation. Simulating the MLSE receiver in optimum form is too time consuming, so we estimated the I-Q path history parameter pk'S by using a simple procedure analogous to decision feedback processing. Although this method is not theoretically equivalent to an optimum computation, our results show that it performs essentially as well as an optimum computation. For moderate to high SNR, an upperbound on the probability of symbol error is obtained, using the concept of error events. A simplified expression for an upperbound on probability of symbol error, for the case when single-error error events are dominant is also obtained. A sub-optimum receiver structure is then derived using average matched filter responses. The sub-optimum receiver which turns out to be a complex filter followed by a decision device, is a relatively simple structure. The performance of the sub-optimum receiver was estimated for two different uplink filters. The effect of varying the BPNL input drive level was also studied. Our simulation results indicate that the performance of both the MLSE and the sub-optimum receivers approach asymptotically the same optimum performance band.</p> <p>Finally, we extend our results on an optimum receiver structure for receiving QPSK signals over a digital satellite communications channel, to include the effects of filtering following the non-linear satellite transponder. It is shown that the complexity of the MLSE receiver is primarily determined by the uplink channel memory. The error performance of the receiver at low signal-to-noise ratios is evaluated by computer simulation. An upperbound on the probability of symbol error at moderate to high SNR is also obtained. A sub-optimum receiver similar to the uplink channel filtering case is developed and its performance evaluated using computer simulation. The degradation in performance of the sub-optimum receiver compared to the optimum receiver is found to be small.</p> / Doctor of Philosophy (PhD)
59

Design and Modelling of Microwave Circuits Using Optimization Methods

Daijavad, Shahrokh 06 1900 (has links)
<p>This thesis addresses itself to the computer-aided design and modelling of microwave circuits using efficient minimax and ℓ₁ optimization techniques.</p> <p>Recent algorithms for nonlinear minimax and ℓ₁ for the particular applications of this thesis. Efficient gradient approximation techniques applicable to both minimax and ℓ₁ optimization are presented.</p> <p>A comparative example with ℓ₂ optimization illustrates the robustness of ℓ₁ for the particular applications of this thesis. Efficient gradient approximation techniques applicable to both minimax and ℓ₁ optimization are presented.</p> <p>A simplified and straightforward treatment of sensitivities for two port networks, cascaded and branched cascaded structures is introduced. The objective is to calculate the sensitivities efficiently, without appealing to the adjoint network concept. A novel proof of a recent result in sensitivity analysis of lossless and reciprocal two-ports is presented.</p> <p>Design of manifold type waveguide multiplexers has been considered as a major application for both minimax optimization and the theoretical work in branched cascaded network sensitivity analysis. Components of the multiplexer structure and nonideal effects such as dissipation and dispersion are discussed and a step-by-step implementation of an algorithm to calculate particular responses and sensitivities is presented. Examples of the design of 3-, 12- and 16-channel, 12 GHz multiplexers illustrate the practicality of the approach presented.</p> <p>A new approach to modelling of microwave devices which exploits the theoretical properties of the ℓ₁ norm is presented. The concept of multi-circuit measurements is introduced and its merits in obtaining unique and self-consistent parameters are discussed. The technique is applied to modelling of multi-coupled cavity filters and GaAs FET's. The application of efficient modelling techniques in developing algorithms for postproduction tuning and in establishing the relationship between physical parameters of a device and its equivalent circuit model parameters is discussed.</p> / Doctor of Philosophy (PhD)
60

Advances in Optimization of Circuits and Systems Using Recent Minimax and ℓ₁ Algorithms

Kellermann, Witold 12 1900 (has links)
<p>This thesis concerns itself with computer-aided techniques for design centering, tolerancing and tuning, fault location and model parameter identification from measurements.</p> <p>Since many of the engineering system problems discussed in this thesis are formulated as optimization problems we examine algorithms and techniques for nonlinear optimization. Our attention is focused on minimax and ℓ₁ algorithms since many formulations of engineering system problems exploit the characteristic features of these two norms.</p> <p>A novel approach for worst-case network design is proposed and an algorithm for the fixed tolerance problem embodying worst-case search and selection of sample points is presented.</p> <p>The features of the ℓ₁ norm in the tuning problem are discussed in detail and explained using necessary conditions for optimality of the nonlinear ℓ₁ problems with nonlinear constraints. Regular and singular ℓ₁ problems are defined and a criterion for determining a singularity present in the ℓ₁ problem is formulated.</p> <p>New formulations using the ℓ₁ norm are given for fault isolation and model parameter identification in analog circuits.</p> <p>Practical engineering problems have been solved illustrating the wide applicability of the concepts used and the robustness of the algorithms employed.</p> <p>A new algorithm for minimizing the cardinality of a set subject to nonlinear, nondifferentiable constraints is presented and illustrated by solving the best mechanical alignment problem. The load shedding and generation rescheduling problem in power systems is formulated using the ℓ₁ norm. The formulation is tested on 6-bus and 26-bus power systems. A general microwave multiplexer design procedure exploiting exact network sensitivities is introduced and illustrated by designing 5-channel, 11 GHz and 12-channel, 12 GHz multiplexers.</p> / Doctor of Philosophy (PhD)

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