Browsing by Author "Goad, Stephen D."

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    An iterative technique for shaped-beam synthesis of unequally spaced, nonuniformly excited linear arrays
    Goad, Stephen D. (Virginia Polytechnic Institute and State University, 1978)
    Antennas with radiation patterns conforming to a specified shape have many applications. Further, precise shaping of the main beam is often required. Array antennas are especially suited for shaped beam synthesis. The purpose of this thesis is to introduce an iterative technique for the shaped-beam synthesis of unequally spaced, nonuniformly excited linear arrays. The technique requires an initial approximation to the desired radiation pattern. This approximation may be attained by any classical synthesis method. Successive iterations are then applied to the initial pattern and are of two types, element current perturbations and element position perturbations. These two iteration types are applied in a variety of sequences and with different weighting functions. Several examples are considered for some typical radiation patterns. In one particular example of a sector pattern both the maximum main beam ripple and sidelobe level are reduced to approximately -40 dB using a 20-element array. Many comparisons are made and the effectiveness of the technique is evaluated.
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    The theory and design of switched-mode power transformers for minimum conductor loss
    Goad, Stephen D. (Virginia Polytechnic Institute and State University, 1985)
    A comprehensive and general analysis of the electromagnetic fields, power dissipation, and energy storage within transformer windings is presented. Emphasis is placed on applications in switched-mode power conversion. One-dimensional radial variation of the field quantities is assumed. The first phase of the investigation is for sinusoidal excitation; solutions for the current density and magnetic field intensity are derived and studied in order to develop a fundamental understanding of the basic phenomena. Expressions for the power dissipation and energy storage in both single- and multi-layer windings are then derived which, upon investigation, yield a technique for minimizing the power dissipation by choosing an optimum conductor thickness. Several levels of accuracy, ranging from exact solutions to very simple and physically meaningful series approximations, are defined and examined to determine their usefulness and range of validity. The time-harmonic treatment is generalized to arbitrary periodic exoitation by means of Fourier analysis, resulting in a powerful extension of its applicability to any possible converter topology. Results for several representative waveshapes are presented from which a fundamental dependence cn the waveform bandwidth is discovered. Practical application of the theoretical analysis is considered by developing models for several couon winding types: single and multi-filar round wire, litz wire, and sheet conductors. Experimental results are presented and compared with the theoretical results for each of these cases. Finally, a design procedure is outlined for switched—mode pour transformers which is based on this work.