Ultrawideband Low-Profile Arrays of Tightly Coupled Antenna Elements

189 Pages·2011·5.89 MB·English

Ultrawideband Low-Profile Arrays of Tightly Coupled
Antenna Elements: Excitation, Termination and Feeding
Methods
Dissertation
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the
Graduate School of The Ohio State University
By
Ioannis Tzanidis, B.S., M.S.
Graduate Program in Electrical and Computer Engineering
The Ohio State University
2011
Dissertation Committee:
John. L. Volakis, Advisor
Kubilay Sertel, Co-advisor
Joel T. Johnson
Fernando Teixeira
Robert Garbacz
(cid:2)c Copyright by
Ioannis Tzanidis
2011
Abstract
The need for high resolution imaging radars and high data rate telecommunications
has direct implications for the employed antennas. Specifically, modern RF front-ends
require ultra-wideband (UWB) performance using low profile antennas for inconspicuous
installation. Otherfunctionalitiessuchasbeamsteeringandmultipleinputmultipleoutput
(MIMO)arehighlydesiredinanefforttocreatediverse,multi-functioningantennasystems.
To this end, antenna arrays have been successfully used for beam steering and MIMO
applications. However, a key limitation is narrow bandwidth and often bulky size (i.e.
non-conformal). Also, in the past, arrays were designed to have minimum mutual coupling.
This itself limited their bandwidth to that of their individual antenna elements.
More recently, a novel class of antennas referred to as “tightly coupled phased arrays”
(TCPAs) were shown to exhibit UWB performance while residing on a thin substrate.
In contrast to traditional arrays, TCPAs utilize the mutual capacitance between array
elements to counteract the ground plane inductance. Typically, TCPAs provide very large
bandwidths (up to 5 : 1) while maintaining small thickness (λ/10 at the lowest operational
frequency). It has been shown that TCPAs are a class of metamaterial antennas, and thus
inherently provide significant wave slow-down that can be harnessed for miniaturization.
This miniaturization can be exploited for bandwidth increase. Specifically, utilization of
the wave slow-down resulted in a novel UWB interwoven spiral array (ISPA) that achieved
10 : 1 bandwidth using λ/23 thickness.
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Although the design of tightly coupled arrays is well understood, for a successful imple-
mentation several key challenges remain to be addressed. Firstly, finite size arrays suffer
from reduced bandwidth due to non-uniform excitation and insufficient mutual coupling.
To alleviate this issue, in this dissertation we propose a novel excitation technique based
on the characteristic modes (CM) of the mutual impedance matrix of the array. Unlike
uniform excitation, the proposed feeding scheme provides for very low active VSWRs for
all array elements, even the ones at the array’s edges. To further improve the finite array
bandwidth we considered termination techniques for the edge elements, including resistive
and short-/open-circuit terminations. Comparisons between these techniques are provided
in terms of the array’s active VSWR, efficiency, realized gain and radiation patterns. We
found that simple short-circuit terminations of the edge elements was the most effective.
A second challenge relates to the feeding of the UWB TCPAs. Specifically, designing
an UWB balun/impedance transformer while conforming to stringent space, weight, cost,
and power constraints is not trivial. To address these issues, we designed a novel UWB feed
with ∼ 4 : 1 bandwidth having an impedance transformation ratio of 50Ω−200Ω (or 4 : 1)
as well.
The above contributions led to the development of a 7×7 tightly coupled dipole array.
Measurements showed that the dipole array can achieve very low VSWR with a measured
realized gain of approximately 3dBi at 200MHz and 7dBi at 600MHz. The aperture
efficiency of the array was numerically estimated at about 90% throughout the 200MHz−
600MHz band.
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This is dedicated to my parents Iakovos-Maria, to my brother Anestis, and to my love
Aspasia
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Acknowledgments
I would like to thank the following friends who have supported me and through our dis-
cussions broadened my perspective on antennas and electromagnetics: Stylianos Dosopou-
los, George Trichopoulos, Erdinc Irci, Tao Peng, Will Moulder, Jon Doane, Faruk Erkmen,
Nathan Smith, Jae Young, Haksu Moon, Jing Zhao, Gil young, Jeff Challas, Ugur Olgun,
Nil Apaydin, and Elias Alwan. And of course the older fellows: Gokhan Mumcu, Salih
Yarga, Yijun Zhou, Brad Kramer and Lanlin Zhang.
Iwouldliketothankseparately, researchersDr. DimitrisPsychoudakisandDr. Stavros
Koulouridis for our discussions on various antenna topics, and for their guidance in con-
ducting antenna measurements. Their support and friendship is very much appreciated.
I would like to thank professors Prof. Robert Garbacz, Prof. Joel Johnson and Prof.
Fernando Teixeira for being my dissertation reading committee and for kindly sharing with
me their perspectives on this work. Also, I would like to thank professors Prof. Jin-Fa Lee,
and Prof. Roberto Rojas for serving in my candidacy exam committee, and Prof. Jin-Fa
Lee, Prof. Roberto Rojas, Dr. Chi-Chih Chen, and Prof. Ed Overman for serving in my
qualifier exam.
I would like to extend my respect and appreciation to Dr. Chi-Chih Chen, who co-
advised me during the first two years at ElectroScience Laboratory. Dr. Chen initiated me
into the mysteries of spiral antennas, antenna miniaturization, and into conducting antenna
measurements. Thank you Chi-Chih.
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I would like to express my gratitude, respect and admiration for my co-advisor Dr.
Kubilay Sertel. Throughout my course at ElectroScience Lab., Kubi has been one of the
mostinfluentialpeopleandarolemodelforme. Hismentorshipandguidanceinconducting
research are invaluable. I wish every student had an advisor like Kubi. Thank you so much
for everything you have done for me Kubi.
I would like to express my gratitude for having Prof. John Volakis as my mentor.
Few people in the world will ever have a chance to study and learn from such a charismatic
professor. IwouldliketothankhimforgivingmetheopportunitytostudyatElectroScience
Laboratoryandforhiscontinuoussupportthroughoutmy5yearsatElectroScience. Thank
you very much Prof. Volakis.
Last but not least, I would like to express my respect to the staff of the ElectroScience
Laboratory because with their hard work and dedication they made my life easier.
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Vita
August 6, 1983 .................................Born - Volos, Greece
2006 ...........................................B.S. Electrical and Computer Engineer-
ing,
Democritus University of Thrace,
Xanthi, Greece
2010 ...........................................M.S. Electrical Engineering,
The Ohio State University,
Columbus, Ohio, USA
2006-present ...................................Graduate Research Associate,
The Ohio State University, Columbus,
Ohio, USA
Publications
Journal Publications
I. Tzanidis, K. Sertel, J. L. Volakis, “Characteristic excitation taper for ultra-wideband
tightly coupled antenna arrays”, accepted for publication in IEEE Transactions Antennas
and Propagation.
N. K. Nahar, J. Y. Chung, I. Tzanidis, K. Sertel, J. L. Volakis, “Optically Transparent
RF-EO Aperture With 20:1 Bandwidth”, Microwave and Optical Technology Letters, Vol.
53, No. 8, 2011.
I. Tzanidis, K. Sertel, J. L. Volakis, “Interweaved Spiral Array (ISPA) With a 10:1 Band-
width on a Ground Plane”, IEEE Antennas and Wireless Propagation Letters, Vol. 10,
2011.
I. Tzanidis, C-C. Chen, J. L. Volakis, “Low Profile Spiral on a Thin Ferrite Ground Plane
for 220-500 MHz Operation”, IEEE Transactions on Antennas and Propagation, Vol. 58,
No. 11, 2010.
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Conference Publications
Nahar, N.K., Tzanidis, I.I., Sertel, K., Volakis, J.L., “Ultra Wideband Transparent RF
Aperture for Electro-Optical Integration”, Antennas and Propagation Symposium, Jul.
2010.
I. Tzanidis, K. Sertel, J. L. Volakis, “An Interweaved Spiral Array (ISPA) Providing a 10:1
Bandwidth Over a Ground plane”, Antennas and Propagation Symposium, Jul. 2010.
J. L. Volakis, K. Sertel, I. Tzanidis, “Small Wideband Antennas Based On Photonic Crys-
tals”, European Conference on Antennas and Propagation, 2010.
J. L. Volakis, J. A. Kasemodel, C.C. Chen, K. Sertel, I. Tzanidis, “Wideband Conformal
Metamaterial Apertures”, International Workshop on Antenna Technology, 2010.
I. Tzanidis, C.-C. Chen, J.L. Volakis, “Low Profile, Cavity Backed Spiral on Thin Fer-
rite Ground Plane for High Power Operation above 200MHz”, Antennas and Propagation
Symposium, Jun. 2009.
I. Tzanidis, C.-C. Chen, J.L. Volakis, “Smaller UWB Conformal Antennas for VHF/UHF
Applications with Ferrodielectric Loadings”, Antennas and Propagation Symposium, Jul.
2008.
I. Tzanidis, S. Koulouridis, K. Sertel, D. Hansford, J.L. Volakis, “Characterization of Low-
Loss Magnetodielectric Composites for Antenna Size Reduction”, Antennas and Propaga-
tion Symposium, Jul. 2008.
I. Tzanidis, C.-C. Chen, J.L. Volakis, “Antenna Miniaturization Using Impedance Matched
Ferrites”, Antenna Measurement Techniques Association, Nov. 2007.
Student Awards
st
1 placeinStudentPaperCompetitioninAntennasandPropagationSymposium,Toronto,
Canada, 2010. Paper title: An Interweaved Spiral Array (ISPA) Providing a 10 : 1 Band-
width Over a Ground plane.
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Honorable mention in Student PaperCompetition in Antennas andPropagation Sympo-
sium, Charleston, SC, USA, 2009. Paper title: Low Profile, Cavity Backed Spiral on Thin
Ferrite Ground Plane for High Power Operation above 200MHz.
Fields of Study
Major Field: Electrical and Computer Engineering
Studies in:
Electromagnetics
Antennas
RF Circuits
Mathematics
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