Radar target tracking problem has been a popular topic for several decades. Recent works have shown that the performance of tracking algorithms increases as more prior information is used by the system / such as maximum velocity and maximum acceleration of the target, altitude of the target, or the elevation structure of the terrain. In this thesis we will focus on increasing the performance of tracking algorithms making use of benefit from the elevation model of the environment where the target tracker is searching. For a constant target altitude and a certain radar location, we generate a &ldquo / visibility map&rdquo / using the elevation model of the terrain and use this information to estimate the location and the time that the target will reappear. The second aim of this work is to use the visibility map information for improving the performance of track initiation. For that purpose, a special map has been formed, that we call as the &ldquo / track initiation probability map&rdquo / , which shows the target first time appearance density. This information has been used at the initialization part of the track initiation algorithm in order to increase the performance.

Detection and tracking of signals used in sonar applications in noisy environment is the focus of this thesis. We have concentrated on the low Signal-to-Noise Ratio (SNR) case where the conventional detection methods are not applicable. Furthermore, it is assumed that the duty cycle is relatively low. In the problem that is of concern the carrier frequency, pulse repetition interval (PRI) and the existence of the signal are not known. The unknown character of PRI makes the problem challenging since it means that the signal exists at some unknown intervals. A recursive, Bayesian track-before-detect (TBD) filter using particle filter based methods is proposed to solve the concerned problem. The data used by the particle filter is the magnitude of a complex spectrum in complex Gaussian noise. The existence variable is added in the design of the filter to determine the existence of the signal. The evolution of the signal state is modeled by a linear stochastic process. The filter estimates the signal state including the carrier frequency and PRI. Simulations are done under different scenarios where the carrier frequency, PRI and the existence of the signal varies. The results demonstrate that the algorithm presented in this thesis can detect signals which cannot be detected by conventional methods. Besides detection, the tracking performance of the filter is satisfying.

Magnetic Resonance Electrical Impedance Tomography (MREIT) reconstructs images of electrical conductivity distribution based on magnetic flux density (B) measurements. Magnetic flux density is generated by an externally applied current on the object and measured by a Magnetic Resonance Imaging (MRI) scanner. With the measured data and peripheral voltage measurements, the conductivity distribution of the object can be reconstructed. There are two types of reconstruction algorithms. First type uses current density distributions to reconstruct conductivity distribution. Object must be rotated in MRI scanner to measure three components of magnetic flux density. These types of algorithms are called J-based reconstruction algorithms. The second type of reconstruction algorithms uses only one component of magnetic flux density which is parallel to the main magnetic field of MRI scanner. This eliminates the need of subject rotation. These types of algorithms are called B-based reconstruction algorithms. In this study four of the B-based reconstruction algorithms, proposed by several research groups, are examined. The algorithms are tested by different computer models for noise-free and noisy data. For noise-free data, the algorithms work successfully. System SNR 30, 20 and 13 are used for noisy data. For noisy data the performance of algorithm is not as satisfactory as noise-free data. Twice differentiation of z component of B (Bz) is used for two of the algorithms. These algorithms are very sensitive to noise. One of the algorithms uses only one differentiation of Bz so it is immune to noise. The other algorithm uses sensitivity matrix to reconstruct conductivity distribution.

In this study, analysis of Magnetic Resonance Imaging (MRI) in inhomogeneous main magnetic field is conducted. A numerical model based on Bloch equation is implemented for MRI, to understand effect of inhomogeneous magnetic field to Magnetic Resonance (MR) signal. Using the model, relations between inhomogeneity levels in main magnetic field with energy, decay time, bandwidth of the FID signal is investigated. Also relation between the magnetic field inhomogeneity and field of view is determined. To simulate measurement noise in the FID signal under inhomogeneous main magnetic field, noise model for MRI with homogeneous main field is altered. Following the numerical model development an image reconstruction algorithm for inhomogeneous main magnetic field is developed to remove undesirable effect of field inhomogeneity in image reconstruction. To evaluate capability of the reconstruction algorithm, the algorithm is tested for several input parameters which results in different noise levels in the FID signal. Then reconstruction errors are analysed to gain information about feasibility of MRI in inhomogeneous main magnetic field.

Magnetic Resonance Electrical Impedance Tomography (MREIT) reconstructs conductivity distribution with internal current density (MRCDI) and boundary voltage measurements. There are many algorithms proposed for the solution of MREIT inverse problem which can be divided into two groups: Current density (J) and magnetic flux density (B) based reconstruction algorithms. In this thesis, J-based MREIT reconstruction algorithms are implemented and optimized with modifications. These algorithms are simulated with five conductivity models which have different geometries and conductivity values. Results of simulation are discussed and reconstruction algorithms are compared according to their performances. Equipotential-Projection algorithm has lower error percentages than other algorithms for noise-free case whereas Hybrid algorithm has the best performance for noisy cases. Although J-substitution and Hybrid algorithms have relatively long reconstruction times, they produced the best images perceptually. v Integration along Cartesian Grid Lines and Integration along Equipotential Lines algorithms diverge as noise level increases. Equipotential-Projection algorithm has erroneous lines starting from corners of FOV especially for noisy cases whereas Solution as a Linear Equation System has a typical grid artifact. When performance with data of experiment 1 is considered, only Solution as a Linear Equation System algorithm partially reconstructed all elements which show that it is robust to noise. Equipotential-Projection algorithm reconstructed resistive element partially and other algorithms failed in reconstruction of conductivity distribution. Experimental results obtained with a higher conductivity contrast show that Solution as a Linear Equation System, J-Substitution and Hybrid algorithms reconstructed both phantom elements and Hybrid algorithm is superior to other algorithms in percentage error comparison.

Microwave and millimeter-wave phase shifters are one of the most important structures of the antenna series that are used in communication and radar applications. They are used to form the main beam of the electronically scanned phase array antennas and generate the appropriate phase values for the antenna elements design while providing electronic beam steering. In this thesis, S-band hybrid 4 bit phase shifter of 22.5&ordm / phase resolution is designed, simulated, fabricated and measured. Bits are separately designed to maintain low phase errors and return loss. In this manner, fabrication and measurements are performed for each bit. These measurements are carried on since each bit reached to its acceptable level of operation. According to the outcomes and acquired knowledge, layout for optimum cascading of 4 bits is developed. Measurement results are compared with simulations and repeatability is tested to observe if it is convenient to use in mass production. Designs and simulations are performed by using ADS2008&reg / .

In this study, a MATLAB&reg / code based on the Shooting and Bouncing Ray (SBR) algorithm is developed to compute the Radar Cross Section (RCS) of complex targets. SBR is based on ray tracing and combine Geometric Optics (GO) and Physical Optics (PO) approaches to compute the RCS of arbitrary scatterers. The presented algorithm is examined in two parts / the first part addresses a new aperture selection strategy named as &ldquo / conformal aperture&rdquo / , which is proposed and formulated to increase the performance of the code outside the specular regions, and the second part is devoted to testing the multiple scattering and shadowing performance of the code. The conformal aperture approach consists of a configuration that gathers all rays bouncing back from the target, and calculates their contribution to RCS. Multiple scattering capability of the algorithm is verified and tested over simple shapes. Ray tracing part of the code is also used as v a shadowing algorithm. In the first instance, simple shapes like sphere, plate, cylinder and polyhedron are used to model simple targets. With primitive shapes, complex targets can be modeled up to some degree. Later, patch representation is used to model complex targets accurately. In order to test the whole code over complex targets, a Computer Aided Design (CAD) format known as Stereo Lithography (STL) mesh is used. Targets that are composed in CAD tools are imported in STL mesh format and handled in the code. Different sweep geometries are defined to compute the RCS of targets with respect to aspect angles. Complex targets are selected according to their RCS characteristics to test the code further. In addition to these, results are compared with PO, Method of Moments (MoM) and Multilevel Fast Multipole Method (MLFMM) results obtained from the FEKO software. These comparisons enabled us to improve the code as possible as it is.

There are many optimization problems motivated by engineering applications, whose constraints and/or cost functions are computationally expensive to evaluate. What is more derivative information is usually not available or available at a considerable cost. For that reason, classical optimization methods, based on derivatives, are not applicable. This study presents a framework based on available methods in literature to overcome this important problem. First, a penalized model is constructed where the violation of the constraints are added to the cost function. The model is optimized with help of stochastic approximation algorithms until a point satisfying the constraints is obtained. Then, a sample point set satisfying the constraints is obtained by taking advantage of direct search algorithms based sampling strategies. In this context, two search direction estimation methods, convex hull based and estimated radius of curvature of the sample point set based methods can be applicable. Point set is used to create a barrier which imposes a large cost for points near to the boundary. The aim is to obtain convergence to local optima using the most promising direction with help of direct search methods. As regards to the evaluation of the cost function there are two directions to follow: a-) Gradient-based methods, b-) Non-gradient methods. In gradient-based methods, the gradient is approximated using the so-called stochastic approximation algorithms. In the latter case, direct search algorithms based sampling strategy is realized. This study is concluded by using all these ideas in the solution of complicated test problems where the cost and the constraint functions are costly to evaluate.

In this thesis, a visual 3-D eye gaze tracker is designed and implemented to tested via computer simulations and on an experimental setup. Proposed tracker is designed to examine human perception on autostereoscopic displays when the viewer is 3m away from such displays. Two different methods are proposed for calibrating personal parameters and gaze estimation, namely line of gaze (LoG) and line of sight (LoS) solutions. 2-D and 3-D estimation performances of the proposed system are observed both using computer simulations and the experimental setup. In terms of 2-D and 3-D performance criteria, LoS solution generates slightly better results compared to that of LoG on experimental setup and their performances are found to be comparable in simulations. 2-D estimation inaccuracy of the system is obtained as smaller than 0.5&deg / during simulations and approximately 1&deg / for the experimental setup. 3-D estimation inaccuracy of the system along x- and y-axis is obtained as smaller than 2&deg / during the simulations and the experiments. However, estimation accuracy along z-direction is significantly sensitive to pupil detection and head pose estimation errors. For typical error levels, 20cm inaccuracy along z-direction is observed during simulations, whereas this inaccuracy reaches 80cm in the experimental setup.

Excellent uniformity and mature material properties of Quantum Well Infrared Photodetectors (QWIPs) have allowed the realization of large format, low cost staring focal plane arrays (FPAs) in various thermal imaging bands. AlGaAs/InGaAs and AlGaAs/GaAs materials systems have been the standard systems for the construction of mid-wavelength infrared (MWIR) and long-wavelength (LWIR) QWIPs. However AlGaAs/GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate (low integration time) and/or low background conditions limiting the application area of standard QWIPs. This thesis focuses on the growth and development of InP based single and dual band QWIP FPAs. We experimentally demonstrate that QWIPs on InP substrates provide important advantages that can be utilized to overcome the bottlenecks of the standard GaAs based QWIP technology. InP/InGaAs material system is an alternative to AlGaAs/GaAs for LWIR QWIPs. We demonstrate a large format (640x512) LWIR QWIP FPA constructed with strained InP/InGaAs material system. The strain introduced to the structure shifts the cut-off wavelength from ~8.5 to 9.7 &micro / m with lambdap=8.9 &micro / m. The FPA fabricated with the 40-well epilayer structure yielded a peak quantum efficiency as high as 12% with a broad spectral response (&amp / #8710 / lambda/lambdap=17%). The peak responsivity of the FPA pixels is larger than 1.4 A/W with conversion efficiency as high as 20% in the bias region where the detectivity is reasonably high (2.6x1010 cmHz1/2/W, f/1.5, 65 K). The FPA providing a background limited performance temperature higher than 65 K (f/1.5) satisfies the requirements of most low integration time/low background applications where AlGaAs/GaAs QWIPs cannot be utilized due to low conversion efficiency and read-out circuit noise limited sensitivity. Noise equivalent temperature differences (NETD) of the FPA are as low as 19 and 40 mK with integration times as short as 1.8 ms and 430 &micro / s (f/1.5, 65 K), respectively. We also experimentally demonstrate that the cut-off wavelength of MWIR AlInAs/InGaAs QWIPs can be tuned in a sufficiently large range in the MWIR atmospheric window by only changing the quantum well (QW) width at the lattice matched composition. The cut-off wavelength can be shifted up to ~5.0 &micro / m with a QW width of 22 &Aring / in which case very broad spectral response (&amp / #8710 / lambda/lambdap=~30%) and a reasonably high peak detectivity is achievable leading to a NETD as low as 14 mK (f/2) with 25 &micro / m pitch in a 640x512 FPA. The advantages of InP based MWIR and LWIR single band QWIPs were combined by growing and fabricating a mid format (320x256) dual band QWIP FPA. The FPA provided NETD (f/1.5, 65 K, 19 ms) values of 27 mK and 29 mK in the MWIR and LWIR modes with an impressively low DC signal nonuniformity of ~ 4%. The results clearly demonstrate that InP based material systems display high potential for MWIR and LWIR single band and MWIR/LWIR dual band QWIP FPAs needed by third generation thermal imagers by overcoming the limitations of the standard GaAs based QWIPs under high frame rate (low integration time) and/or low background conditions.