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Antennas A Platform for Antenna Optimization with Numerical Electromagnetics Code Incorporated with Genetic Algorithms This is the full text of a Master's thesis by Second Lieutenant Timothy L. Pitzer, USAF, AFIT/GE/ENG/06-46, which was presented to the Faculty Department of Electrical and Computer Engineering of Air University's Air Force Institute of Technology (AFIT), in March 2006. This thesis investigation presents a unique incorporation of the Method of Moments (MoM) with a Genetic Algorithm (GA). A GA is used in accord with the Numerical Electromagnetics Code, Version 4 (NEC4) to create and optimize typical wire antenna designs, including single elements and arrays. Design parameters for the antenna are defined and encoded into a chromosome composed of a series of numbers. The cost function associated with the specific antenna of interest is what quantifies improvement and, eventually, optimization. This cost function is created and used by the GA to evaluate the performance of a population of antenna designs. The most successful designs of each generation are kept and altered through crossover and mutation. Through the course of generations, convergence upon a best design is attained. The Yagi-Uda and the Log Periodic Dipole Array (LPDA) antennas are the focus of this study. The objectives for each antenna are to maximize the main power gain while minimizing the Voltage Standing Wave Ratio (VSWR) and the antenna's length. Results for the Yagi-Uda exceed previous designs by as much as 40 dB in the main lobe while maintaining respectable length and VSWR values. The improvements made in the LPDA antenna were not as drastic, finding a nominal increase in power gain while truncating original allowance in the length by more than half, along with nominal VSWR values that were close to the ideal value of one. The percentage of bandwidth covered for the frequencies of interest are 8.11% for the Yagi-Uda and 10.7% for the LPDA. GA performance is evaluated and, based on previous results, implemented with real-numbered chromosomes as opposed to the classic binary encoding. This methodology is very robust and is improved upon in this research, all while using a novel approach with an optimization program platform called iSIGHT, developed by Engineous Software. [Taken from abstract]. The full text is available in PDF format on the Scientific and Technical Information Network (STINET) which is provided by the Defense Technical Information Center (DTIC). Finite Difference Time Domain (FDTD) Analysis of a Leaky Traveling Wave Microstrip Antenna This is the full text of a Master's thesis by First Lieutenant Gregory M. Zelinski, USAF, AFIT/GE/ENG/05-24, which was presented to the Faculty Department of Electrical and Computer Engineering of Air University's Air Force Institute of Technology (AFIT), in March 2005. This thesis provides the groundwork that will enable the development of a lightweight, inexpensive, aerodynamic, and broadband antenna. Whether for radar or communication, an antenna with these properties would be a force multiplier for the smaller, limited payload air vehicles the United States Air Force will pursue in the coming years. Several microstrip antennas using the first higher order mode were simulated with the Finite-Difference Time-Domain (FDTD) method. The propagation constant of each antenna was extracted from the resulting field distribution for comparison with a transverse resonance approximation, measured far-field patterns, and other simulated antennas. Variations of the geometry were explored to investigate field propagation, improve the far-field pattern, and improve bandwidth. A simplified fabrication method was demonstrated that shortens production time and improves the far-field pattern. [Taken from abstract]. The full text is available in PDF format on the Scientific and Technical Information Network (STINET) which is provided by the Defense Technical Information Center (DTIC). |
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