DESIGN AND TESTING OF HELICAL ANTENNAS FOR A RF TEST FACILITY A Thesis presented ...

202 Pages·2012·8.62 MB·English

DESIGN AND TESTING OF HELICAL ANTENNAS FOR A RF TEST FACILITY
_______________________________________
A Thesis
presented to
the Faculty of the Graduate School
at the University of Missouri-Columbia
_______________________________________________________
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
_____________________________________________________
by
MIKE YOUNG
Dr. Randy Curry, Thesis Supervisor
MAY, 2012
The undersigned, appointed by the dean of the Graduate School,
have examined the Thesis entitled
DESIGN AND TESTING OF HELICAL ANTENNAS FOR A RF TEST FACILITY
Presented by Mike B Young
A candidate for the degree of
MASTER OF SCIENCE IN ELECTRICAL ENGINEERING
And hereby certify that, in their opinion, it is worthy of acceptance.

Professor Dr. Randy Curry, ECE
Professor Dr. Carmen Chicone, MATH
Professor Dr. Gregory Triplett, ECE
Professor Dr. Justin Legarsky, ECE
This thesis would notA ChKavNe OWbeLenE DpGoEssMibEleN TwSit hout the guidance, support,
encouragement, and pressure from Dr. Randy Curry. Dr. Curry has been a wonderful influence
in my life, and I would not be where I am today without him. I am deeply indebted to him for
all that he has done for me.
I am extremely appreciative of the help that Dr. Bob Druce has given me throughout his
involvement at the University of Missouri-Columbia. His office door is always open, and he is
always more than willing to help anyone who walked in. I have taken much advantage of this,
and am very grateful.
None of this could have been accomplished if it weren't for the help of our lab
supervisor, Bill Carter. Bill's management abilities, leadership skills, and charm meant that if
something needed to be accomplished around lab, Bill would be the one who could produce
results.
My good friend Stan Ikpe has literally been a lifesaver throughout my college career.
The friendship and moral support that he has provided over the years has been the source of
my motivation. Having gone through undergraduate and graduate school together, we have
shared many cherished memories. Stan has been, and always will be, a wonderful friend.
I am also grateful to many of my fellow students, both graduate and undergraduate,
who have supported me on this project. Very few things in life can be accomplished on your
own as easily as they can with the help from wonderful people around you.
I would finally like to acknowledge the help from family. Without their continued
support, this would have not been possible.
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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ................................................................................................................................. ii
TABLE OF CONTENTS .................................................................................................................................... iii
LIST OF FIGURES ............................................................................................................................................ v
LIST OF TABLES ............................................................................................................................................. xi
ABSTRACT .................................................................................................................................................... xii
1. INTRODUCTION TO RF FACILITIES ......................................................................................................... 1
2. ANTENNA BACKGROUND ...................................................................................................................... 6
2.1 Radiation Mechanism ................................................................................................................... 7
2.2 Radiation Patterns ...................................................................................................................... 10
2.3 Field Regions ............................................................................................................................... 14
2.4 Power Density ............................................................................................................................. 16
2.5 Beamwidth .................................................................................................................................. 18
2.6 Directivity .................................................................................................................................... 19
2.7 Efficiency ..................................................................................................................................... 20
2.8 Gain ............................................................................................................................................. 21
2.9 Realized Gain ............................................................................................................................... 22
2.10 Polarization ................................................................................................................................. 23
2.11 Friis Transmission Equation ........................................................................................................ 24
2.12 Radar Cross Section..................................................................................................................... 25
2.13 Radar Range Equation ................................................................................................................. 26
2.14 S and VSWR .............................................................................................................................. 27
11
3. HELICAL ANTENNAS ............................................................................................................................ 29
3.1 Introduction to Helical Antennas ................................................................................................ 30
3.2 Modes of Operation .................................................................................................................... 32
3.2.1 Helical Transmission Modes................................................................................................ 33
3.2.2 Normal Mode ...................................................................................................................... 34
3.2.3 Axial Mode .......................................................................................................................... 36
3.3 Performance Optimization .......................................................................................................... 38
3.3.1 Maximum Gain .................................................................................................................... 39
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3.3.2 Optimal Circumference ....................................................................................................... 40
3.3.3 Optimal Ground Plane ........................................................................................................ 41
4. HELICAL ANTENNA DESIGN ............................................................................................................... 45
4.1 Initial Simulation ......................................................................................................................... 46
4.2 First Build .................................................................................................................................... 50
4.3 Dielectric-Loaded CST Simulations .............................................................................................. 56
4.4 Design Modifications .................................................................................................................. 59
4.5 Optimized Turns Ratio Construction ........................................................................................... 62
4.6 Commercial Results ..................................................................................................................... 67
4.7 Bandwidth Improvements .......................................................................................................... 69
5. EQUIPMENT & MEASUREMENTS ........................................................................................................ 77
5.1 Anechoic Chamber ...................................................................................................................... 77
5.2 Equipment ................................................................................................................................... 84
5.3 Gain Measurements .................................................................................................................... 86
5.4 Turntable ..................................................................................................................................... 89
6. CONCLUSION ..................................................................................................................................... 146
APPENDIX A - MATLAB CODE FOR CALCULATING ANTENNA GAIN........................................................ 152
APPENDIX B - MATLAB CODE FOR TURNTABLE BASED POLAR PLOTS ................................................... 157
APPENDIX C - "360° ANTENNA" REPORT ................................................................................................ 167
Bibliography .............................................................................................................................................. 185

iv
LIST OF FIGURES

Figure 1: The University of Missouri-Columbia's anechoic chamber ............................................ 1
Figure 2: Block diagram for basic antenna testing ........................................................................ 2
Figure 3: Typical display from a Tektronix RSA6100A scope ......................................................... 3
Figure 4: The basic half-wave dipole antenna [4] ......................................................................... 8
Figure 5: Formation and detachment of electric field lines for short dipole [5] ......................... 10
Figure 6: The three-dimensional antenna coordinate system [6] ................................................ 11
Figure 7: The two-dimensional polar plot of Figure 6 ................................................................. 12
Figure 8: The three-dimensional omnidirectional pattern of a dipole antenna .......................... 13
Figure 9: The reactive-near, radiating-near, and far-field regions [8] ......................................... 15
Figure 10: Example of half-power beamwidth and first-null beamwidth [13] ............................ 19
Figure 11: Example of typical S parameters for an antenna ..................................................... 28
11
Figure 12: Helical antenna geometry ........................................................................................... 32
Figure 13: Instantaneous charge distribution for transmission modes: (a) The lowest order
mode T (normal mode); (b) The first order mode T (axial mode) [37] ................... 33
0 1
Figure 14: Normal mode helix operation ..................................................................................... 34
Figure 15: Equivalent model a helical antenna consisting of small loops and short dipoles
connected in series ..................................................................................................... 35
Figure 16: Axial mode helical operation ...................................................................................... 37
Figure 17: The maximum antenna gain as a function of the normalized antenna length [41] ... 39
Figure 18: Gain vs. length and turn radius, with turn spacing .24 lambda [42] .......................... 41
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Figure 19: Helical antenna above (a) infinite ground plane, (b) square conductor, (c) cylindrical
cup, and (d) truncated cone [32] ............................................................................... 42
Figure 20: Gain for various shapes of the ground conductors shown in Figure 19 [32] ............. 43
Figure 21: CST CAD helix geometry .............................................................................................. 46
Figure 22: The directivity profile at 850 MHz of a 4.5" diameter air-core helical model ........... 48
Figure 23: The polar form of the directivity profile shown above ............................................... 48
Figure 24: First PVC build ............................................................................................................. 52
Figure 25. S parameters of first 4.0" PVC helical build ............................................................. 52
11
Figure 26: Picture of the cardboard core antenna designed for 918 MHz .................................. 54
Figure 27: S parameters of the new cardboard core antenna designed for 918 MHz ............. 55
11
Figure 28. Updated CAD model of Figure 21 that now includes a PVC tube with ε =2.73.......... 56
r
Figure 29: 4.5" Air-core helical at 850 MHz from Chapter 4.1 .................................................... 57
Figure 30. 4.5" dielectric-loaded Helical at 850 MHz .................................................................. 58
Figure 31: Measured relative permittivity of PVC ....................................................................... 61
Figure 32: Relative phase velocity p for different pitch angles α as a function of the helix
circumference in free-space wavelengths C for the condition of in-phase fields in
λ
the axial direction[31] ................................................................................................. 61
Figure 33: Relative antenna sizes around the same diameter PVC core using (a) normal pitch
angle, (b) optimized pitch angle ................................................................................ 63
Figure 34: Expected axial gain with and without optimized scaling ............................................ 63
Figure 35: Comparison of the far-field patterns at the low frequency end of 416 MHz using (A)
normal scaling and (B) optimized scaling ................................................................... 65
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Figure 36: Comparison of the far-field patterns at the high frequency end of 850 MHz using
(A) normal scaling and (B) optimized scaling .............................................................. 66
Figure 37: Measured antenna impedance vs. frequency ............................................................ 69
Figure 38: Measured S parameters of 918 MHz air-core helical antenna with and without a
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transformer ................................................................................................................. 72
Figure 39: Measured S parameters of the 3" 1.01 GHz optimized dielectric-loaded helical with
11
transformer ................................................................................................................. 73
Figure 40: Measured S parameters of the 2" 1.5 GHz optimized PVC dielectric-loaded helical
11
with transformer ......................................................................................................... 73
Figure 41: Measured S parameters of the 1.5" 1.85 GHz optimized PVC dielectric-loaded
11
helical with transformer ............................................................................................. 74
Figure 42: Measured S parameters of the 1" 2.61 GHz optimized PVC dielectric-loaded helical
11
with transformer ......................................................................................................... 74
Figure 43: A picture of the five class of constructed helical antennas. ....................................... 76
Figure 44: (a) The Jaumann Sandwich uses a staggered array of resistive sheets. For the case of
normal incidence, it can be modeled using the transmission line model shown in (b).
(c) Pyramidal absorber, with an incident ray .............................................................. 80
Figure 45: Smith chart matching the transmission line of Figure 44(b) ...................................... 81
Figure 46: One of the helicals inside our Jaumann-absorber-lined anechoic chamber that was
manufactured and installed by Panashield ................................................................ 83
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Figure 47: Schematic showing the RSA connected to a helical on a turntable, radiating into the
commercial LP-80 log-periodic that is connected to a signal generator, all within the
anechoic chamber ....................................................................................................... 84
Figure 48: Example output of the RSA-6411A sweeping from 100 MHz - 3 GHz ........................ 86
Figure 49: LP80 manufacturer provided gain vs. the measured gain .......................................... 89
Figure 50: SolidWorks cross-section view of the turntable design ............................................. 90
Figure 51: Composite turntable photo ........................................................................................ 91
Figure 52: Turntable interface screenshot................................................................................... 92
Figure 53: A CST simulated example of the differences between the far-field patterns on the (a)
vertical and (b) horizontal planes for the E field of the 4" cardboard-core antenna at
Φ
766 MHz whose measured results are presented later on ........................................ 94
Figure 54: Commercial measured horizontal polar plot at 1.6 GHz ............................................. 95
Figure 55: UMC measured horizontal polar plot at 1.6 GHz........................................................ 96
Figure 56: CST simulated horizontal polar plot at 1.6 GHz .......................................................... 97
Figure 57: Commercial measured vertical polar plot at 1.6 GHz ................................................. 98
Figure 58: UMC measured vertical polar plot at 1.6 GHz ............................................................. 99
Figure 59: CST simulated vertical polar plot at 1.6 GHz ............................................................ 100
Figure 60: Commercial measured horizontal polar plot at 1.3 GHz .......................................... 102
Figure 61: UMC measured horizontal polar plot at 1.3 GHz...................................................... 103
Figure 62: CST simulated horizontal polar plot at 1.3 GHz ........................................................ 104
Figure 63: Commercial measured vertical polar plot at 1.3 GHz ............................................... 105
Figure 64: UMC measured vertical polar plot at 1.3 GHz .......................................................... 106
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Figure 65: CST simulated vertical polar plot at 1.3 GHz ............................................................ 107
Figure 66: Commercial measured horizontal polar plot at 1.10 GHz ......................................... 108
Figure 67: UMC measured horizontal polar plot at 1.10 GHz .................................................... 109
Figure 68: CST simulated horizontal polar plot at 1.10 GHz ...................................................... 110
Figure 69: Commercial measured vertical polar plot at 1.10 GHz ............................................. 111
Figure 70: UMC measured vertical polar plot at 1.10 GHz ........................................................ 112
Figure 71: CST simulated vertical polar plot at 1.10 GHz .......................................................... 113
Figure 72: Commercial measured horizontal polar plot at 566 MHz ......................................... 115
Figure 73: UMC measured horizontal polar plot at 566 MHz .................................................... 116
Figure 74: CST simulated horizontal polar plot at 566 MHz ...................................................... 117
Figure 75: Commercial measured vertical polar plot at 566 MHz ............................................. 118
Figure 76: UMC measured vertical polar plot at 566 MHz ........................................................ 119
Figure 77: CST simulated vertical polar plot at 566 MHz........................................................... 120
Figure 78: Commercial measured horizontal polar plot at 666 MHz ......................................... 121
Figure 79: UMC measured horizontal polar plot at 666 MHz .................................................... 122
Figure 80: CST simulated horizontal polar plot at 666 MHz ...................................................... 123
Figure 81: Commercial measured vertical polar plot at 666 MHz ............................................. 124
Figure 82: UMC measured vertical polar plot at 666 MHz ........................................................ 125
Figure 83: CST simulated vertical polar plot at 666 MHz........................................................... 126
Figure 84: Commercial measured horizontal polar plot at 766 MHz ........................................ 127
Figure 85: UMC measured horizontal polar plot at 766 MHz..................................................... 128
Figure 86: CST simulated horizontal polar plot at 766 MHz ...................................................... 129
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