design and optimization of electrically small antennas for high frequency

124 Pages·2014·3.31 MB·English

by  Jim Baker

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

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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
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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.
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TABLEOF 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
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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
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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. Performance for three-arm HMLA, direction of helical coils modified ............. 45
Table 7. Helical MLA and Toroidal Helical Performance ............................................... 52
Table 8. Fractal Tree Performance at 20 MHz, one meter height ..................................... 63
Table 9. Fractal Tree and Helical Fractal Tree Performance ............................................ 66
Table 10. Hilbert Curve Simulated Performance .............................................................. 70
Table 11. Baseline and GA Optimized Performance ........................................................ 80
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List of Figures
Figure 1: Landing Craft Air Cushion (LCAC) .................................................................. 2
Figure 2: Normalized wave resistance ............................................................................. 12
Figure 3: Normalized wave reactance .............................................................................. 12
Figure 4: Current distribution for λ/4, λ/8, and λ/20 monopole antennas ....................... 15
Figure 5: Chu and Hansen/Collin limits with shortened monopoles from Table 1 ......... 16
Figure 6: LabVIEW program for Genetic Algorithms .................................................... 19
Figure 7: LabVIEW program for controlling HP8753B Network Analyzer ................... 19
Figure 8: FEKO display for early ESA prototype ........................................................... 20
Figure 9: Performance of established designs, Q(ka) ...................................................... 22
Figure 10: NEC model of Marconi’s 1904 toploaded antenna ........................................ 23
Figure 11: Monopole antenna over PEC ground (left) and with mesh toploading (right)25
Figure 12: Current distribution for monopole with and without toploading ................... 26
Figure 13: Two-arm and three-arm folded monopole antennas ....................................... 29
Figure 14: Folded meandering line antenna with three arms ........................................... 30
Figure 15: The concept of inner toploading ..................................................................... 33
Figure 16: One-turn helical with inner toploading. ......................................................... 35
Figure 17: Current Magnitude, helical antenna with and without inner toploading. ....... 35
Figure 18: One-turn helical with inner toploading. ......................................................... 36
Figure 20: Simulated and measured S11with and without inner toploading ................... 37
Figure 19: Prototype helical antenna with inner toploading ............................................ 37
Figure 21: Helical meandering line antenna .................................................................... 39
Figure 22: Impedance, helical MLA, 3 – 30 MHz ........................................................... 40
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Figure 23: Impedance, helical MLA, 30 – 100 MHz ....................................................... 40
Figure 24: Far-field radiation pattern ............................................................................... 42
Figure 25: Current magnitude in three-arm helical MLA ................................................ 43
Figure 26: Current Magnitude in one arm ....................................................................... 44
Figure 27: Current Phase in one arm ............................................................................... 44
Figure 28: HMLA single arm, original (left), modified with alternating turns (right) .... 45
Figure 29: One-turn toroidal helical antenna ................................................................... 46
Figure 30: Impedance for one-turn toroidal helical antenna ............................................ 47
Figure 31: Gain for one-turn toroidal helical antenna ..................................................... 47
Figure 32: One-turn toroidal helical antenna with two-turn inner toploading ................. 48
Figure 33: Impedance for one-turn toroidal helical antenna with inner toploading ........ 49
Figure 34: Gain for one-turn toroidal helical antenna with inner toploading .................. 49
Figure 35: Toroidal helical antenna with four half-turn folded arms .............................. 50
Figure 36: Impedance for half-turn toroidal helical antenna, four folded arms............... 51
Figure 37: Gain for half-turn toroidal helical antenna, four folded arms ........................ 51
Figure 38: Generator for a Koch curve ............................................................................ 54
Figure 39: Koch antennas after one and two iterations .................................................... 54
Figure 40: Sierpinski Triangle from IFS .......................................................................... 55
Figure 41: Fractal tree from IFS ...................................................................................... 55
Figure 42: Fractal tree antennas, iteration #2 and #3 ....................................................... 56
Figure 43: Fractal tree antenna with two arms, iteration #4 ............................................ 57
Figure 44: Fractal tree antenna with three arms, iteration #4 .......................................... 58
Figure 45: Fractal tree antenna with four arms, iteration #4............................................ 59
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Figure 46: Helical fractal tree with two arms, iteration #1 .............................................. 60
Figure 47: Helical fractal tree with two arms, iteration #2 .............................................. 61
Figure 48: Comparison of fractal tree geometries ........................................................... 62
Figure 49: Impedance for four-arm fractal tree ............................................................... 64
Figure 50: Current Magnitude for four-arm fractal tree .................................................. 64
Figure 51: Gain pattern for four-arm fractal tree ............................................................. 65
Figure 52: Hilbert curves ................................................................................................. 67
Figure 53: Antenna, Hilbert curve, one iteration ............................................................. 68
Figure 54: Antenna, Hilbert curve, second iteration ........................................................ 69
Figure 55: Antenna Prototype, Hilbert curve, second iteration ....................................... 70
Figure 56: Simulated and measured S11 for Hilbert prototype ....................................... 71
Figure 57: Simulated and measured Impedance for Hilbert prototype ............................ 71
Figure 58: GA optimized model ...................................................................................... 79
Figure 59: Q and input resistance for four-arm GA ......................................................... 80
Figure 60: Impedance, baseline design ............................................................................ 81
Figure 61: Impedance, GA optimized design .................................................................. 81
Figure 62: Improvement in Q .......................................................................................... 82
Figure 63: Improvement in effective radius..................................................................... 82
Figure 64: Simulated and measured S11, open circuit mode over lossy ground ............. 87
Figure 65: Simulated and measured S11, short circuit mode over lossy ground ............. 87
Figure 66: Simulated and measured HPBW .................................................................... 88
Figure 67: Measuring antenna patterns near Hanauma Bay ............................................ 89
Figure 68: Received power measured over azimuth ........................................................ 90
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