profile wide scan angle phased array antenna

112 Pages·2015·7.07 MB·English

by  Henry H. Vo

DEVELOPMENT OF AN ULTRA-WIDEBAND LOW-
PROFILE WIDE SCAN ANGLE PHASED ARRAY
ANTENNA

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the
Degree Doctor of Philosophy in the Graduate School of
The Ohio State University
By
Henry H. Vo, B.S., M.S.
Graduate Program in Electrical and Computer Engineering
The Ohio State University
2015

Dissertation Committee:

Prof. Chi-Chih Chen, Advisor

Prof. John Volakis, Co-Advisor

Prof. Joel T. Johnson
© Copyright by
Henry H. Vo
2015
Abstract

Coupling in phased arrays is a major issue. Mutual coupling causes both gain and
bandwidth reduction. Such coupling arises from the presence of adjacent elements that
produce scattering and losses during low-angle beam steering. The scattering effect is
comprised of (1) structural scattering and (2) antenna-mode coupling and associated
losses. Losses occur when the coupled energy received by adjacent elements is dissipated
at the back-end loads, resulting in lower gain at wide scan angles. In addition, the
interference from periodic nature of large arrays or feed networks may produce undesired
scattering modes and traveling waves that limit the upper bound of the operational
frequency and maximum scan angle in ultra-wideband (UWB) arrays. As a result, current
ultra wideband (UWB) array designs typically have limited scanning to no more than 45°
from normal.
In this dissertation, we examine the low angle scanning issues. These issues are
verified via full-wave simulation. Our studies show that mutual coupling in the H-plane is
stronger than in the E-plane, likely due to the dipole element pattern shape.
Another focus of this dissertation is the development of an UWB dual-
polarization and low angle beam steering array based on the concept of tightly coupled
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dipole arrays. For this array, we suppress/minimize mutual coupling by redesigning the
antenna element, feed geometry, and array structure. Some key design parameters include
(1) the simple feed of tightly-coupled dipoles, (2) array height above ground plane, (3)
dielectric superstrate, and (4) parasitic coupling ring. The common mode issue is avoided
by retaining the ground plane height to less than λ /4 and the array unit cell size to
mid
0.45λ . The final design is also fabricatable on a low-cost PCB. The PCB uses (1) 0.35
high
mils thick copper corresponding to a standard ¼ oz. copper lamination, (2) 2 mils
coupling slot width and plated-thru vias manufacturable using standard PCB process, and
(3) standard Roger RT/Ruroid 5880LZ substrate with dielectric constant of 1.96 and
Roger RT/Duroid 5880 superstrate with dielectric constant of 2.2.
An 18x18 prototype array is fabricated and measured to verify the final design.
The total array height of the fabricated prototype is 0.122λ at the lowest operating
frequency. It is also demonstrated that the fabricated array is capable of scanning down to
more than 60° in the E- and H-planes with impedance bandwidth of 2.62:1 subject to
VSWR ≤ 2. Good agreement was also observed between simulations and measurements.

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Dedication

Dedicated to my family

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Acknowledgements

I dedicate this dissertation to my parents, my sisters, and my brothers, for their
hard work and constant support throughout my education. Without their support, I would
not have what I have today.
I am thankful to my advisor, Dr. Chi-Chih Chen for his support, encouragement,
guidance, and endless patience throughout my time and work at the ElectroScience Lab
(ESL). I thank him for sharing of his expertise and teaching me the key points of antenna
design, antenna miniaturization, and as well as antenna measurement. It is my honor to
have such an outstanding advisor and to be his research group member. I would also like
to thank my co-advisor, Dr. John Volakis for the advice and motivation I have received
from him. Thanks Dr. Joel Johnson for his valuable suggestions on this dissertation and
for his participating on all my examination committee.
Very special thanks go to Dr. Teh-Hong Lee for his friendship and providing me
all the valuable information in antenna measurement. I would like to express my very
special thanks to Patricia Toothman for her endless support, advice, and guidance.
Thanks to all my friends at ESL for their friendships and insightful discussions in
research as well as in course-work.

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Vita

December 31, 1974………………………….….…. Born – Quang Nam, Vietnam
2002……………………………………………….. B.S. Electrical Engineering, Cal Poly
State University
2008……………………………………………..… M.S. Electrical Engineering, Cal
Poly State University
2004-2006…………………………………………. Microwave Engineer, L-3
Com/Randtron Antenna Systems
2006-2009…………………………………………. R&D Engineer, Space Systems/Loral
2009-2011…………………………………………. Sr. R&D Engineer, Space
Systems/Loral
2011-present………………………………………. Graduate Research Associate, The
Ohio State University

Publications
H. H. Vo and C.C. Chen, “A Very Low-Profile UWB Phased Array Antenna Design for
Supporting Wide Angle Beam Steering,” in review.
H. H. Vo and C.C. Chen, “Frequency and Scan Angle Limitations in UWB Phased Array,”
European Conference on Antenna and Propagation (EUCAP), Hague, Netherlands, Apr.
2014.
H. H. Vo and C.C. Chen, “Causes of Low Scanning Angle Issues in Phased Array Antennas,”
Antennas Measurement Technique Association (AMTA), Columbus, OH, Oct. 2013.
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N. K. Host, H. H. Vo, and C.C. Chen, “Causes of Low Scanning Angle Issues in Phased
Array Antennas,” Antennas and Propagation Society International Symposium, Orlando, FL,
Jul. 2013.

Fields of Study

Major Field: Electrical and Computer Engineering
Studies in:
Electromagnetics
Microwave/Antenna Design and Measurement
RF Circuits
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Table of Contents

Abstract ............................................................................................................................................ ii
Dedication ....................................................................................................................................... iv
Acknowledgements .......................................................................................................................... v
Vita.................................................................................................................................................. vi
Table of Contents .......................................................................................................................... viii
List of Tables ................................................................................................................................... x
List of Figures ................................................................................................................................. xi
Chapter 1: Introduction .................................................................................................................... 1
Chapter 2: Wide-Angle Scanning and Bandwidth Issues/Limitations of Phased Array Antennas .. 6
2.1 Mutual Coupling in Phased Arrays ........................................................................................ 6
2.2 Low-Angle Scanning Issues ................................................................................................... 7
2.2.1 Antenna Structure Mode Scattering Issue ....................................................................... 9
2.2.2 Absorption by Adjacent Elements ................................................................................ 11
2.2.3 Antenna Mode Scattering ............................................................................................. 13
2.3 Bandwidth and Wide Scan Angle Limitations ..................................................................... 15
2.3.1 Lattice Scattering Mode in Scatter Array ..................................................................... 15
2.3.2 Lattice Scattering Mode in Phased Arrays .................................................................... 18
Chapter 3: Development of Wide Scan Angle Phased Array ........................................................ 26
3.1 Revisiting TCDA Operational Principles............................................................................. 27
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3.1.1 Ground Plane Effect in Ideal TCD Array ..................................................................... 28
3.2 Wide Scan Angle Array Design Procedure .......................................................................... 33
3.2.1 Tightly-Coupled Array Element Design ....................................................................... 33
3.2.2 Feeding Lines ................................................................................................................ 36
3.2.3 Effect of Array Height on Wide Scan Angle ................................................................ 38
3.2.4 Effect of Element Pattern on Wide Scan Angle ............................................................ 41
3.2.5 Effect of Mutual Coupling on Wide Scan Angle .......................................................... 42
3.2.6 Effect of Parasitic Ring ................................................................................................. 46
3.3 Design Parameter Tolerance Analysis ................................................................................. 48
3.3.1 Element-to-Element Coupling Slot Width Tolerance Study ......................................... 48
3.3.2 Bonding Layer Thickness Tolerance Study .................................................................. 50
3.3.3 Feed-line Diameter Tolerance Study ............................................................................ 51
3.4 Summary .............................................................................................................................. 53
Chapter 4: Prototype Measurement ............................................................................................... 54
4.1 Finalized 18x18 Dual-Pol UWB Array Prototype Design ................................................... 54
4.2 Array Assembly ................................................................................................................... 57
4.3 Array Design Verification .................................................................................................... 61
4.4 18x18 Array Prototype Measurement Results ..................................................................... 62
Chapter 5: Conclusion and Future Work ....................................................................................... 75
Appendix A: Array Pattern Synthesis ............................................................................................ 80
A.1 Finite Array Pattern Synthesis (Amplitude Distribution) ................................................... 83
A.1.1 Fast Array Pattern Synthesis using Element Patterns .................................................. 85
A.2 Array Patterns Synthesized Using PSO .............................................................................. 87
Bibliography .................................................................................................................................. 91

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