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Design and Optimization of Electrically Small Antennas for High Frequency (Hf) Applications

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Design and Optimization of Electrically Small Antennas for High Frequency (Hf) Applications DESIGN AND OPTIMIZATION OF ELECTRICALLY SMALL ANTENNAS FOR HIGH FREQUENCY (HF) APPLICATIONS A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ELECTRICAL ENGINEERING DECEMBER 2014 By James M. Baker Dissertation Committee: Magdy F. Iskander, Chairperson Zhengqing Yun David Garmire Victor Lubecke John Madey Keywords: Compact HF, Coastal Radar, Electrically Small Antennas Copyright By James M. Baker 2014 ii ABSTRACT This dissertation presents new concepts and design approaches for the development and optimization of electrically small antennas (ESA) suitable for high frequency (HF) radio communications and coastal surface wave radar applications. For many ESA applications, the primary characteristics of interest (and limiting factors) are lowest self- resonant frequency achieved, input impedance, radiation resistance, and maximum bandwidth achieved. The trade-offs between these characteristics must be balanced when reducing antenna size in order to retain acceptable performance. The concept of “inner toploading” is introduced and utilized in traditional and new designs to reduce antenna ka and resonant frequencies without increasing physical size. Two different design approaches for implementing the new concept were pursued and results presented. The first design approach investigated toroidal and helical designs, including combinations of toroidal helical antennas, helical meandering line antennas, and additional designs incorporating toploading and folding to improve performance. The other approach investigated fractal-based designs in two and three dimensions to improve performance, reduce size, and lower resonant frequency. The performance characteristics of fractal geometries were analyzed and compared with non-fractal designs of similar height, total wire length, and ka. Inner toploading was also applied in the two design approaches and shown to reduce antenna Q by up to a factor of 4 with a corresponding increase in input resistance by up to a factor of 10, when properly applied. When folded arms were applied to various designs, Q was further decreased by a factor of 2 with a corresponding increase in input resistance proportional to the number of arms. Genetic algorithms were developed for optimizing antenna designs and used in custom programs, including a new iii cost function for better comparison of ESA performance. Antenna performance was modeled, analyzed, and optimized using set performance criteria. Several unique antenna designs were simulated and experimentally tested in field measurements. Experimentation was conducted using full-size prototypes with performance measured using vector network analyzers and HF transceivers. Experimental performance measurements were reproduced in simulation models with a high degree of correlation. Successful two-way radio communications were established with amateur radio stations around the world using prototype antennas. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................................................. iii LIST OF TABLES ......................................................................................................................................vii LIST OF FIGURES .................................................................................................................................. viii ACRONYMS ...............................................................................................................................................xii CHAPTER 1 INTRODUCTION ................................................................................................................. 1 A. BACKGROUND ....................................................................................................................................... 1 B. OBJECTIVE ............................................................................................................................................ 3 C. ORGANIZATION...................................................................................................................................... 4 CHAPTER 2 ELECTRICALLY SMALL ANTENNAS............................................................................ 6 A. BACKGROUND ....................................................................................................................................... 6 B. PROPERTIES .......................................................................................................................................... 7 C. DESIGN PRINCIPLES .............................................................................................................................. 14 CHAPTER 3 METHODS OF SOLUTION .............................................................................................. 17 A. NUMERICAL ELECTROMAGNETICS CODE (NEC) .......................................................................................... 17 B. LABVIEW .......................................................................................................................................... 18 C. FEKO ................................................................................................................................................ 20 CHAPTER 4 EVALUATION OF ESTABLISHED DESIGNS AND METHODS ............................... 21 A. ESTABLISHED DESIGNS .......................................................................................................................... 21 B. TOPLOADING ....................................................................................................................................... 23 C. FOLDING ............................................................................................................................................ 28 D. SUMMARY .......................................................................................................................................... 31 CHAPTER 5 NEW CONCEPT AND DESIGN APPROACHES ........................................................... 32 A. BACKGROUND ..................................................................................................................................... 32 B. INNER TOPLOADING.............................................................................................................................. 33 C. NEW DESIGN METHODOLOGY ................................................................................................................ 38 D. NOVEL DESIGNS FOR ELECTRICALLY SMALL HF ANTENNAS ........................................................................... 39 v E. INVESTIGATION OF FRACTAL GEOMETRIES ................................................................................................. 53 F. SUMMARY .......................................................................................................................................... 72 CHAPTER 6 ALGORITHMS FOR DESIGN OPTIMIZATION .......................................................... 74 A. RANDOM SEARCH ................................................................................................................................ 74 B. NELDER-MEAD DOWNHILL SIMPLEX ALGORITHM ....................................................................................... 74 C. SIMULATED ANNEALING (SA) ................................................................................................................. 75 D. GENETIC ALGORITHMS (GA) .................................................................................................................. 75 E. SUMMARY .......................................................................................................................................... 83 CHAPTER 7 EXPERIMENTAL VERIFICATION ................................................................................ 84 A. FIELD TEST CONFIGURATIONS ................................................................................................................. 84 B. FIELD MEASUREMENTS ......................................................................................................................... 85 CHAPTER 8 SUMMARY AND CONCLUSIONS .................................................................................. 98 CHAPTER 9 FUTURE WORK ............................................................................................................... 101 REFERENCES .......................................................................................................................................... 102 APPENDIX A – ENGLISH TRANSLATION OF HILBERT (1891) ...................................................A-1 APPENDIX B – FRACTAL GEOMETRY ............................................................................................. B-1 vi List of Tables Table 1. Shortened Monopole Performance ..................................................................... 14 Table 2. Toploaded λ/4 Monopole Performance .............................................................. 25 Table 3. MLA Performance .............................................................................................. 30 Table 4. Design Analysis for Inner Toploading................................................................ 34 Table 5. Helical MLA Performance.................................................................................. 41 Table 6.
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