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.

Table of Contents

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

2.1 Dielectric structures with antennas showing the location of the slot and the dipole	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

3.1 Efficiency of the single slot and dipole on a grounded, electrically thick, dielectric substrate plotted as a function of substrate thickness	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

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

4.12 Power distribution for slots and dipoles on a 4-2.4-13-4-13 layered substrate

79

4.14 Beam pattern of slots and dipoles on a 4-2.4-13-4-14 layered substrate

82

4.16 Beam pattern of slots and dipoles on a 13-1-13-1-13 layered substrate and comparison of various losses

86

4.20 H-plane pattern for a 13-2.4-13 substrate measurement with air gap.

93

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 er = 13 layered substrate

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