Magneto-Dielectric Wire Antennas Theory and Design

213 Pages·2013·5.85 MB·English

by  Tom Sebastian

Magneto-Dielectric Wire Antennas
Theory and Design
by
Tom Sebastian

A Dissertation Presented in Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy

Approved May 2013 by the
Graduate Supervisory Committee:

Rodolfo Diaz, Chair
George Pan
James Aberle
Michael Kozicki

ARIZONA STATE UNIVERSITY
August 2013
ABSTRACT

There is a pervasive need in the defense industry for conformal, low-profile,
efficient and broadband (HF-UHF) antennas. Broadband capabilities enable shared
aperture multi-function radiators, while conformal antenna profiles minimize physical
damage in army applications, reduce drag and weight penalties in airborne applications
and reduce the visual and RF signatures of the communication node. This dissertation is
concerned with a new class of antennas called Magneto-Dielectric wire antennas
(MDWA) that provide an ideal solution to this ever-present and growing need.
Magneto-dielectric structures ( ) can partially guide

electromagnetic waves and radiate them by leaking off the structure or by scattering
from any discontinuities, much like a metal antenna of the same shape. They are
attractive alternatives to conventional whip and blade antennas because they can be
placed conformal to a metallic ground plane without any performance penalty.
A two pronged approach is taken to analyze MDWAs. In the first, antenna circuit
models are derived for the prototypical dipole and loop elements that include the effects
of realistic dispersive magneto-dielectric materials of construction. A material selection
law results, showing that: (a) The maximum attainable efficiency is determined by a
single magnetic material parameter that we term the hesitivity: Closely related to Snoek’s
product, it measures the maximum magnetic conductivity of the material. (b) The
maximum bandwidth is obtained by placing the highest amount of loss in the
frequency range of operation. As a result, high radiation efficiency antennas can be
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obtained not only from the conventional low loss (low ) materials but also with highly
lossy materials ( ( ) ).

The second approach used to analyze MDWAs is through solving the Green
function problem of the infinite magneto-dielectric cylinder fed by a current loop. This
solution sheds light on the leaky and guided waves supported by the magneto-dielectric
structure and leads to useful design rules connecting the permeability of the material to
the cross sectional area of the antenna in relation to the desired frequency of operation.
The Green function problem of the permeable prolate spheroidal antenna is also solved as
a good approximation to a finite cylinder.

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To my teachers and my family

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Ring the bells that still can ring.
Forget your perfect offering.
There is a crack in everything.
That is how the light gets in.
- Leonard Cohen
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TABLE OF CONTENTS
Page
LIST OF TABLES ................................................................................................................... ix
LIST OF FIGURES .................................................................................................................. x
CHAPTER
1. INTRODUCTION ....................................................................................................... 1
2. DIELECTRIC DIPOLE ANTENNA: CIRCUIT MODEL AND
RADIATION EFFICIENCY .................................................................................. 12
2.1 Introduction .............................................................................................. 12
2.2 Capacitor/ Condenser Antenna ................................................................ 16
2.3 Dielectric Monopole (Capacitive Feed) .................................................. 19
2.4 Radiation Efficiency of a Lossy Dielectric Dipole ................................. 24
3. MAGNETO-DIELECTRIC DIPOLE ANTENNA: CIRCUIT MODEL
AND RADIATION EFFICIENCY ........................................................................ 35
3.2 Historical Development of Permeable Antennas .................................... 37
3.3 Radiation Efficiency of an Electrically Small Magneto-
dielectric Dipole Antenna .............................................................................. 40
3.4 Full-wave Simulations of the Magneto-dielectric Dipole
Antenna .......................................................................................................... 50
3.5 Magneto-dielectric Dipole Prototype ...................................................... 55
3.6 A Note on the Duality between Material Dipoles ................................... 58
3.7 Summary, Conclusions and Future Work ............................................... 60
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4. MAGNETO-DIELECTRIC LOOP ANTENNA: CIRCUIT MODEL AND
RADIATION EFFICIENCY .................................................................................. 62
4.1 Introduction .............................................................................................. 62
4.2 Circuit model ........................................................................................... 63
4.3 Full-wave Simulations of the Magneto-dielectric Loop
Antenna .......................................................................................................... 69
4.4 Practical Application of the Circuit Model: Body Wearable
Belt Antenna ................................................................................................... 73
4.5 Summary, Conclusions and Future Work .............................................. 82
5. MATERIAL SELECTION RULEFOR MAGNETO-DIELECTRIC
ANTENNA DESIGNS ........................................................................................... 84
5.1 Introduction .............................................................................................. 84
5.2 Classification of Magnetic Materials: Dia, Para, Ferro, Ferri
and Anti-Ferro ................................................................................................ 86
5.3 Fundamental Physical Limits in Designing Low Profile &
Conformal Electrically Small Magneto-dielectric Material
Antennas ......................................................................................................... 91
5.4 Hesitivity and Magneto-Dielectric Antenna Radiation
Efficiency ..................................................................................................... 100
5.5 Material Selection Law in the design of magneto-dielectric
antennas ........................................................................................................ 106
5.6 Some Realistic and Almost Realistic Magneto-dielectric
materials Evaluated using the Material Selection Law ............................... 109
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5.7 Conclusions and Future Work ............................................................... 114
6. MAGNETO-DIELECTRIC DIPOLE ANTENNA: CIRCUIT MODEL
USING POLARIZABILITY ................................................................................ 115
6.1 Introduction ............................................................................................ 115
6.2 Polarizability and Antenna Capacitance .............................................. 117
6.3 Factor Relating Polarizability and Antenna Capacitance of a
Permable Prolate Spheroid Antenna ............................................................ 120
6.4 Circuit Model Comparison with Full-Wave Simulations ..................... 128
6.5 Summary and Conclusions ................................................................... 131
7. INFINITELY LONG MAGNETO_DIELECTRIC CYLINDER AS A
MAGNETIC RADIATOR .................................................................................... 132
7.1 Introduction ............................................................................................ 132
7.2 Infinite Magneto-Dielectric Cylinder Wave Equation
Solution ........................................................................................................ 134
7.3 Effective Length for a Finite Magneto-dielectric Dipole
Based on the Radiated Power of an Infinite Magneto-dielectric
cylinder ......................................................................................................... 147
7.4. Summary, Conclusions and Future Work ............................................ 156
8. FINITE MAGNETO-DIELECTRIC PROLATE SPHEROIDAL
ANTENNA ANALYSIS ...................................................................................... 159
8.1 Introduction ........................................................................................... 159
8.2 Prolate Spheroidal Antenna Problem Statement ................................... 161
8.3 Solution of the Wave Equation .............................................................. 162
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8.4 Comparison with Full-Wave Simulations ............................................ 173
8.5 Summary and Future Work ................................................................... 177

REFERENCES ................................................................................................................... 178
APPENDIX
A. DERIVATION OF THE INTERNAL FIELD SHAPE CORRECTION
FACTOR TO ACCOUNT FOR THE EFFECT OF SKIN DEPTH ................. 182
B. DERIVATION OF EFFICIENCY OF A PERMEABLE DIPOLE
FOLLOWING THE APPROACH BY DeVORE et. al. (Ref. 15) ................... 185
C. HELMHOLTZ VECTOR WAVE EQUATION IN PROLATE
SPHEROIDAL COORDINATES UNDER CIRCULAR ( )
SYMMETRY ........................................................................................................ 189

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LIST OF TABLES

Table Page
2-1 TM01 onset/cutoff frequency for a 1cm radius dielectric cylinder for different . ..20
4-1 TE01 onset/cutoff frequency for a 0.5” wire radius magneto-dielectric cylinder
for different and . .............................................................................................70
5-1 Typical Hesitivities of Microwave materials ............................................................100
5-2 Hesitivity of the materials being evaluated using the material selection rule ..........111
7-1 values for different .....................................................................................150
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