2010 APS_ Broadband Characteristics of A Dome Dipole Antenna

Broadband Characteristics of a Dome-Dipole Antenna

Jing Zhao, Chi-Chih Chen, Dimitris Psychoudakis, and John L. Volakis

ElectroScience Laboratory
Department of Electrical and Computer Engineering
The Ohio State University
Columbus, Ohio 43212
{zhao.189,chen.118,psychoudakis.1,volakis.1}@osu.edu

July 15, 2010

Outline

Body-of-Revolution Dome-Dipole Antenna

Motivation
Numerical Formulations and Antenna Description
Calculation Results and Experimental Validations
Optimization of Inverted-Hat Antenna Using Genetic Algorithm
Concluding Remarks

z
t=N
BOR
N
N −1
z N −2

ˆ
t
ˆ
t φ
Ei
y
S
φ
ρ
x
3
2
1
t=0

Broadband Characteristics of a Dome-Dipole Antenna IEEE APS/URSI Symposium, July 2010, Toronto 2/19

Motivation

UWB Antenna of 100:1 Bandwidth


Motivation


UWB operation from low VHF band up to several GHz
Commercial services: WLAN, UMTS (up to 5 GHz)
Military communications: JTRS, SINGARS, UHF SATCOM, and
EPLRS (30-3000 MHz)


Motivation


EPLRS (30-3000 MHz)

Limitations of conventional designs
Several radiators of various sizes and shapes
Protruding for low frequency operation
Sidelobes dominate radiation patterns at high frequencies


Motivation


EPLRS (30-3000 MHz)

Limitations of conventional designs
Several radiators of various sizes and shapes
Protruding for low frequency operation
Sidelobes dominate radiation patterns at high frequencies

Dome-dipole antenna
A single aperture (24” wide and 20” tall) generates VP radiation and
provides consistent dipole-like pattern over 100:1 bandwidth.


Motivation

Body-of-Revolution (BoR) Antenna Fast Analysis


Motivation

Limitations of commercial MoM solvers
3-D meshing: memory-demanding & time-consuming for electrically large
structure

3-D mesh (FEKO)

Motivation

Limitations of commercial MoM solvers
3-D meshing: memory-demanding & time-consuming for electrically large
structure

BoR antenna solver
Using BoR principle (3-D ⇒ 2-D + Fourier modes analysis) to eﬃciently
evaluate axi-symmetry antenna performance.

10

5

z (in)
0

−5

−10
−12 −8 −4 0 4 8 12
ρ (in)

3-D mesh (FEKO) 2-D mesh (BoR)


Basis Function Expansion

Surface currents on a BoR [1]:
Longitudinal direction (ˆ) : piecewise linear (triangle)
t
ˆ a ﬁnte Fourier series
Azimuthal direction (φ):
z ∞ N
t=N t t φ φ
BOR
N
J(r ) = [aαn Jαn (r ) + aαn Jαn (r )]
N −1 α=−∞ n=1
z N −2

ˆ
t
ˆ
t φ
Jαn (r ) = ˆ(r )fn (t)e jαφ
t
t
Ei
y
φ ˆ
Jαn (r ) = φ(r )fn (t)e jαφ
S
φ
ρ t φ
x Unknowns: aαn & aαn for mode α and
3
2 basis function n.
1
t=0
[1] J. R. Mautz and R.F. Harrington, “Radiation and scattering from bodies of revolution,” Appl. Sci. Res. vol. 20, Jun 1969.



Excitation

The antenna feed is modelded by a delta gap source:
V0
ˆ
△z z : r =0
E i (r ) =
0 : else

φ-independent excitation: α = 0
mode only
+ No coupling between the t-directed
currents and the φ-directed currents
∆z I O E i V0
in
aαn = 0 (Iφ = 0)
φ
0
z
V0
- Antenna input impedance: Zin = Iin
x y



Matrix System

Employing Galerkin’s method in conjuction with BoR principle, the matrix
system for each mode α is given by
tφ
Ztt
α Zα It
α
t
Vα
= .
Zφt
α Zφφ
α Iφ
α
φ
Vα
Utilizing the property of vertically polarized feed, the above equation
ﬁnally reduces to

Ztt · It = V0 .
0 0
t

Solve for It to determine surface currents J(r ) and far-zone radiated
0
electric ﬁeld via

jωµ e −jkr ′
E (r ) = − J(r ′ )e jkˆ·r d r ′ .
r
4π r V



24” wide and 20” tall BoR Dome-Dipole Antenna

3-D version of the ﬂare dipole
Exponentially tapered outer surface for constant impedance
z = 1.7(e 0.161y − 1)
Small electrical separation between the upper and bottom surfaces for
uniform radiation pattern

z

x y


Calculation Results and Experimental Validation

Electrical Performance of the 24”×20” Dome-Dipole
Antenna (30 MHz-2 GHz)

Calculations and measurements are in reasonably good agreement
VSWR<3 from 180 MHz to 2 GHz (fed to 50 Ω coaxial cable)
Stable realized gain (θ = 90◦ ) at high frequencies
8 10
Simulation (FEKO)
7 Simulation (BOR) 5
Measurement
6 0

Realized Gain, dBi
5 −5
VSWR

4 −10

3 −15

2 −20
Simulation (FEKO)
1 −25 Simulation (BOR)
Measurement
0 −30
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Frequency, GHz Frequency, GHz

VSWR Realized Gain (θ = 90◦ )


Computational Eﬃciency Improvement
Computing platform
Intel R CoreTM 2 Duo Processor with 3 GHz and 4 GB RAM

Moderate size problem (30 MHz-2 GHz)
Frequency sweep: 41 equally spaced sampling points
FEKO: 1,116s v.s. BoR: 155s
7.2 times eﬃciency improvement

Electrically large problem (6 GHz, i.e. 12λ × 10λ)
Solver # of unknowns CPU time (s)
FEKO 101,310 5,306
BoR 249 56

Unknowns reduction: 400 times & CPU time reduction: 100 times!


Elevation Plane Patterns (Single Main Lobe)
0o 0o 0o 0o
330o 30o 330o 30o 330o 30o 330o 30o

o o o o o o o
300 60 300 60 300 60 300 60o

270
o −30 −20 −10 90o 270
o −30 −20 −10 90o 270
o −30 −20 −10 90o 270
o −30 −20 −10 90o
dB dB dB dB

240 o 120o 240 o 120o 240 o 120o 240 o 120o

o o o o
210o 150 210o 150 210o 150 210o 150
180o 180o 180o 180o

f = 100 MHz f = 2 GHz f = 4 GHz f = 6 GHz

0o 0o 0o 0o
330o 30o 330o 30o 330o 30o 330o 30o

300o 60o 300o 60o 300o 60o 300o 60o

270
o −30 −20 −10 90o 270
o −30 −20 −10 90o 270
o −30 −20 −10 90o 270
o −30 −20 −10 90o
dB dB dB dB

240o 120o 240o 120o 240o 120o 240o 120o

o o o o
210o o
150 210o o
150 210o o
150 210o o
150
180 180 180 180

f = 8 GHz f = 10 GHz f = 12 GHz f = 14 GHz


Measured Gain along the Horizon (2 GHz-14 GHz)

Measured realized gain at θ = 90◦ is almost greater than 0 dB from 2 GHz
to 14 GHz, increasing to 4 dB

10
Measurement
0 dB
5
Realzied Gain, dBi

0

−5

−10

−15

−20
2 3 4 5 6 7 8 9 10 11 12 13 14
Frequency, GHz



Optimization of Inverted-Hat Antenna

Inverted-Hat Antenna (IHA)
A novel compact frequency-scaled structure for broadband operation with
properly designed outer surface growth proﬁle [2].

[2] J. Zhao, C.-C. Chen and J. L. Volakis, “Frequency-Scaled UWB Inverted-Hat Antenna,” IEEE Trans. Antennas Propagat.,
vol. 58, no. 7, pp. 2447-2451, Jul, 2010.



Optimization of Inverted-Hat Antenna

Inverted-Hat Antenna (IHA)
A novel compact frequency-scaled structure for broadband operation with
properly designed outer surface growth proﬁle [2].

Goal: constant gain, constant impedance and uniform radiation
pattern across a large BW
Approach: genetic algorithm (GA)
Design Parameters: width, global proﬁle, curvature and # of
elliptical segments

[2] J. Zhao, C.-C. Chen and J. L. Volakis, “Frequency-Scaled UWB Inverted-Hat Antenna,” IEEE Trans. Antennas Propagat.,
vol. 58, no. 7, pp. 2447-2451, Jul, 2010.



Cost Function

COST = αreal Preal + αimag Pimag + αdir Pdir + αripple Pripple



Cost Function


Preal : Resistance (R) ⇒ constant
1
Preal = |R(f ) − avg (R(f ))|2 , αreal = 0.5
Nf
Nf

Nf : total number of discrete frequencies



Cost Function


Pimag : Reactance (X) ⇒ 0
1
Pimag = |X (f )|, αimag = 0.5
Nf
Nf




Cost Function


Preal : Resistance (R) ⇒ constant
1
Preal = |R(f ) − avg (R(f ))|2 , αreal = 0.5
Nf
Nf

Pimag : Reactance (X) ⇒ 0
1
Pimag = |X (f )|, αimag = 0.5
Nf
Nf




Cost Function (cont’d)






Pdir : Maximation of directivity gain (Prefer 5 dB)

1 G (f ) : if G (f ) < 5 dB
Pdir = − Pdir (f ), Pdir =
Nf 5 dB : else
Nf

αdir = 0.8





Pripple : Minimization of gain ripples across the band
1
Pripple = |G (f ) − avg (G (f ))|2 , αripple = 10
Nf
Nf





Pdir : Maximation of directivity gain (Prefer 5 dB)

1 G (f ) : if G (f ) < 5 dB
Pdir = − Pdir (f ), Pdir =
Nf 5 dB : else
Nf

αdir = 0.8

Pripple : Minimization of gain ripples across the band
1
Pripple = |G (f ) − avg (G (f ))|2 , αripple = 10
Nf
Nf



Optimization of 6” tall IHA on Inﬁnite Ground Plane
GA program setup
Population size: 16
Selection: Tournament
Crossover: Uniform
Mutation rate: 0.05
Maximum # of generation : 20

IHA parameter coding
# of bits in a chromosome: 13
Width 10”, 12”, 14”, ..., 36”, 38”, 40”, 4 bits
Global Proﬁle convex/concave, 1 bit
Curvature 0.1, 0.2, ..., 0.9, 1, 1.5, 2, 2.5, 3, 4, 5, 4 bits
# of Ellipse 3, 5, 7, ..., 29, 31, 33 4 bits



6” tall IHA Optimization (200 MHz - 2 GHz)
Optimized IHA using GA for constant gain and impedance
Profile of 6" tall IHA
10
Optimized IHA using GA
8 IHA Published by Zhao, etc. [2]
Width Global Proﬁle Curvature # of Ellipse 6

H, in
12” convex 0.1 33 4
2
0
−16 −12 −8 −4 0 4 8 12 16
W, in

15 150
Optimized IHA using GA Resistance − Optimized IHA using GA
IHA Published by Zhao, etc. [2] 125 Reactance − Optimized IHA using GA
Resistance − IHA Published by Zhao, etc. [2]
Reactance − IHA Published by Zhao, etc. [2]
10 100

Impedance (Ω)
Directivity (dB)

75

5 50

25

0 0

−25

−5 −50
0 0.5 1 1.5 2 0 0.5 1 1.5 2
Frequency (GHz) Frequency (GHz)



6” tall IHA Optimization (1 GHz - 6 GHz)
Optimized IHA using GA for constant gain and impedance
Profile of 6" tall IHA
10
Optimized IHA using GA
8 IHA Published by Zhao, etc. [2]
Width Global Proﬁle Curvature # of Ellipse 6

H, in
28” convex 0.8 31 4
2
0
−16 −12 −8 −4 0 4 8 12 16
W, in

15 175
Optimized IHA using GA Resistance − Optimized IHA using GA
IHA Published by Zhao, etc. [2] 150 Reactance − Optimized IHA using GA
125 Resistance − IHA Published by Zhao, etc. [2]
Reactance − IHA Published by Zhao, etc. [2]
10 100

Impedance (Ω)
75
Directivity (dB)

50
5
25
0

0 −25
−50
−75
−5 −100
1 2 3 4 5 6 1 2 3 4 5 6
Frequency (GHz) Frequency (GHz)


Concluding Remarks

Summary


Concluding Remarks

Summary
A dome-dipole antenna is designed, fabricated and validated to provide
consistent dipole-like pattern over 100:1 bandwidth using 24”×20”
aperture. It is rugged and simple for ground vehicle communication
systems


Concluding Remarks

Summary
systems

Utilizing body-of-revolution (BoR) principle, compared to the commercial
3-D MoM solver FEKO, the computational eﬃciency is improved by a
factor of 100 when evaluating the performance of an electrically large
dome-dipole antenna (12λ × 10λ)


Concluding Remarks

Summary
systems

Utilizing body-of-revolution (BoR) principle, compared to the commercial
3-D MoM solver FEKO, the computational eﬃciency is improved by a
factor of 100 when evaluating the performance of an electrically large
dome-dipole antenna (12λ × 10λ)

Incorporating BoR method and genetic algorithm (GA), a 6” tall
inverted-hat antenna (IHA) is optimized for constant impedance and gain
performance


2010 APS_ Broadband Characteristics of A Dome Dipole Antenna

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