A STUDY OF SLOT AND DIPOLE ANTENNAS ON LAYERED
ELECTRICALLY THICK DIELECTRIC SUBSTRATES
FOR FAR INFRARED AND MILLIMETER
WAVE IMAGING ARRAYS
by
Robert Lowell Rogers, M.S.E., B.Sc.
DISSERTATION
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
DOCTOR OF PHILOSOPHY
THE UNIVERSITY OF TEXAS
May 1989
Copyright Robert Lowell Rogers, May 1989
ABSTRACT
Robert Lowell Rogers, PhD
The University of Texas at Austin, 1989
Supervising Professor: Dr. Dean P. Neikirk
An approach for designing imaging array antennas built on electrically thick substrates is presented. Calculations and measurements of the radiation properties and the input impedances of slot and dipole antennas on electrically thick, grounded, dielectric substrates are presented. These structures offer the possibility of simplifying the fabrication of imaging array antenna structures which operate at millimeter wave and far infrared freqeuncies. They also offer the possibility of good beam patterns which can be tailored to suit a specific need. We present an analysis of practical layered structures which have beam patterns that are suitable for millimeter wave and far-infrared imaging array applications. We discuss considerations of the choice of dielectric layers with regard to beam patterns, surface wave losses, and the type of element used. The effects of dielectric and ground plane losses in high-gain structures are also considered. Efficiencies and beam patterns for three and five layer structures are presented, although the analysis techniques are extendable to an arbitrary number of layers. It is found that in combination with the use of a twin element configuration, both slot and dipole antennas can overcome the problems of losses to surface waves in the substrate. Consequently, they can be made to efficiently radiate to air on these layered dielectric structures. A microstrip feed structure for the twin slot antenna is also presented along with impedance calculations. It is found that the slot antenna has an input impedance that is compatible with existing detectors that operate at the millimeter wave and far infrared frequencies. Measurements of beam patterns and input impedance were made at X-band, and it was found that the models used here agreed reasonably well with the measurements.
1. Introduction ......... 1
2 Analysis ......... 7
2.1 Introduction ......... 7
2.2 Radiation Analysis ......... 9
Radiation to Air ......... 10
Guided Waves ......... 16
2.3 Reciprocity and Spectral Domain Analysis ......... 19
Coupling by Reciprocity ......... 22
Spectral Domain Analysis ......... 28
3 Broadside Twin Elements ......... 34
3.1 Introduction ......... 34
3.2 Electrically Thick Substrates ......... 35
3.3 Twin Elements ......... 43
3.4 Thicker Substrates ......... 49
3.5 Conclusions ......... 53
4 Layered Substrates ......... 56
4.1 Introduction ......... 56
4.2 Three Layer Case ......... 57
4.3 Five Layer Case ......... 78
4.4 Beam Pattern Measurements ......... 85
4.5 Conclusion ......... 92
5 Impedance of Slot Antennas ......... 96
5.1 Introduction ......... 96
5.2 Single Slot Results ......... 98
Calculations ......... 98
Measurements ......... 98
Results ......... 100
5.3 Twin Slots ......... 105
6 Conclusions ......... 110
link for Appendix A-C .
Appendix A: Far-Field Calculation ......... 113
Appendix B: Derivation of Spectral Domain Green's Functions ......... 117
Appendix C: Basis Functions and Microstrip Formulas ......... 121
Bibliography ......... 124
List of Figures
Chapter 2
8 | |
2.2 Transmission line model for the spectral components of the sources |
12 |
2.3 Twin slot with feed network | 20 |
2.4 Transmission line model with the surface for application of the reciprocity theorem | 23 |
Chapter 3
36 | |
3.2 Power distribution for the slot and dipole on a grounded electrically thick dielectric substrate plotted as a function of substrate thickness |
37 |
3.3 Efficiency of a single slot and a single dipole as a function of normalized frequency on a quarter wavelength thick substrate |
40 |
3.4 Power distribution of a single slot and a single dipole as a function of normalized frequency on a quarter wavelength thick substrate |
41 |
3.5 Efficiency of twin slots and twin dipoles as a function element separation on a quarter wavelength thick substrate |
44 |
3.6 Efficiency of twin slots as a function of normalized frequency on a quarter wavelength thick substrate |
44 |
3.7 Power distribution of broadside-spaced twin slot and twin dipole antennas on a quarter wavelength thick substrate |
46 |
3.8 Radiation pattern in the substrate of single and twin slots on a quarter wavelength thick substrate |
47 |
3.9 Beam patterns for slot antennas on a quarter wavelength thick substrate |
48 |
3.10 Beam patterns for dipoles on a quarter wavelength thick substrate |
50 |
3.11 Efficiency of twin slots and twin dipoles as a function of element separation on three and five quarter wavelength thick substrates |
51 |
3.12 Beam patterns for single slot and dipole elements on three and five quarter wavelength thick substrates |
54 |
Chapter 4
4.1 Power distribution for slots and dipoles on a 13-2.4-13 layered
substrate
|
61 |
4.2 Efficiency of slots and dipoles on a 13-2.4-13 layered substrate |
63 |
4.3 Beam pattern of slots and dipoles on a 13-2.4-13 layered substrate |
64 |
4.4 Power distribution of slots and dipoles on a 13-1-13 layered substrate |
67 |
4.5 Efficiency of slots and dipoles on a 13-1-13 layered substrate |
68 |
4.6 Beam pattern of slots and dipoles on a 13-1-13 layered substrate |
69 |
4.7 Power distribution for slots and dipoles on a 4-2.4-13 layered substrate |
70 |
4.8 Efficiency of slots and dipoles on a 4-2.4-13 layered substrate |
72 |
4.9 Beam pattern of slots and dipoles on a 4-2.4-13 layered substrate 74
4.10 Efficiency of slots and dipoles on a 4-4-13 layered substrate 76
4.11 Beam pattern of slots and dipoles on a 4-4-13 layered substrate 77
4.12 Power distribution for slots and dipoles on a 4-2.4-13-4-13 layered substrate |
79 |
4.13 Efficiency of slots and dipoles on a 4-2.4-13-4-13 layered substrate 80
4.14 Beam pattern of slots and dipoles on a 4-2.4-13-4-14 layered substrate |
82 |
4.15 Efficiency of slots and dipoles on a 13-1-13-1-13 layered substrate 84
4.16 Beam pattern of slots and dipoles on a 13-1-13-1-13 layered substrate and comparison of various losses |
86 |
4.17 H-plane pattern for a 4-4-13 substrate measurement 88
4.18 H-plane pattern for a 13-2.4-13 substrate measurement 89
4.19 H-plane pattern for a 4-2.4-13-4-13 substrate measurement 91
4.20 H-plane pattern for a 13-2.4-13 substrate measurement with air gap. |
93 |
Chapter 5
5.1 Single slot with microstrip feed on a layered supporting substrate 97
5.2 Circuit used to measure the impedance of the slot antenna 99
5.3 Impedance measurements of a slot with a single supporting dielectric
substrate
|
101 |
5.4 Impedance measurements for a slot with a 4-2.4-13 supporting dielectric
substrate
|
102 |
5.5 Impedance calculation of a single slot with a 4-2.4-13-4-13 layered
substrate
|
104 |
5.6 Impedance calculation of a single slot on an |
104 |
5.7 Impedance calculation of a single slot on a 13-2.4-13 substrate |
106 |
5.8 Impedance calculation of twin slots on an er = 4 substrate |
108 |