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 LaboratoryDepartment of Electrical and Computer Engineering

The Ohio State UniversityColumbus, Ohio 43212

zhao.189,chen.118,psychoudakis.1,[email protected]

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

t

φ

ρφ

z

~Ei

1

2

3

y

x

z

t = 0

t = N

N

N − 1

N − 2

t

BOR

S

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, andEPLRS (30-3000 MHz)


Motivation





Limitations of conventional designs

Several radiators of various sizes and shapes

Protruding for low frequency operation

Sidelobes dominate radiation patterns at high frequencies


Motivation





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 andprovides 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 largestructure

3-D mesh (FEKO)


Motivation


Limitations of commercial MoM solvers

3-D meshing: memory-demanding & time-consuming for electrically largestructure

BoR antenna solver

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

3-D mesh (FEKO)

−12 −8 −4 0 4 8 12−10

−5

0

5

10

ρ (in)

z (in

)

2-D mesh (BoR)



Basis Function Expansion

Surface currents on a BoR [1]:

Longitudinal direction (t) : piecewise linear (triangle)

Azimuthal direction (φ): a finte Fourier series

t

φ

ρφ

z

~Ei

1

2

3

y

x

z

t = 0

t = N

N

N − 1

N − 2

t

BOR

S

~J(~r) =∞

∑

α=−∞

N∑

n=1

[atαn

~Jtαn(~r) + aφ

αn~Jφ

αn(~r)]

~Jtαn(~r) = t(~r)fn(t)e

jαφ

~Jφαn(~r) = φ(~r)fn(t)e

jαφ

Unknowns: atαn & a

φαn for mode α and

basis function n.


[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:

~E i (~r) =

V0z

z : ~r = 0

0 : else

O

+

-

V0∆z ~EiIin

y

z

x

φ-independent excitation: α = 0mode only

No coupling between the t-directedcurrents and the φ-directed currents

aφαn = 0 (Iφ0 = 0)

Antenna input impedance: Zin = V0Iin



Matrix System

Employing Galerkin’s method in conjuction with BoR principle, the matrixsystem for each mode α is given by

[

Zttα Ztφ

α

Zφtα Zφφ

α

]

[

ItαIφα

]

=

[

Vtα

Vφα

]

.

Utilizing the property of vertically polarized feed, the above equationfinally reduces to

Ztt0 · It0 = Vt

0.

Solve for It0 to determine surface currents ~J(~r) and far-zone radiatedelectric field via

~E (~r) = −jωµ

4π

e−jkr

r

∫∫∫

V

~J(~r ′)e jkr ·~r ′d~r ′.



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(e0.161y − 1)

Small electrical separation between the upper and bottom surfaces foruniform radiation pattern

y

z

x


Calculation Results and Experimental Validation

Electrical Performance of the 24”×20” Dome-DipoleAntenna (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

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

1

2

3

4

5

6

7

8

Frequency, GHz

VS

WR

Simulation (FEKO)Simulation (BOR)Measurement

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2−30

−25

−20

−15

−10

−5

0

5

10

Frequency, GHz

Rea

lized

Gai

n, d

Bi

Simulation (FEKO)Simulation (BOR)Measurement

VSWR Realized Gain (θ = 90)Broadband Characteristics of a Dome-Dipole Antenna IEEE APS/URSI Symposium, July 2010, Toronto 9/19


Computational Efficiency Improvement

Computing platform

Intel R©CoreTM2 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 5,306BoR 249 56

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



Elevation Plane Patterns (Single Main Lobe)

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

f = 100 MHz f = 2 GHz

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

f = 8 GHz f = 10 GHz

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

f = 4 GHz f = 6 GHz

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

0o

180o

90o270o

30o

150o

60o

120o

330o

210o

300o

240o

−10−20−30dB

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 GHzto 14 GHz, increasing to 4 dB

2 3 4 5 6 7 8 9 10 11 12 13 14−20

−15

−10

−5

0

5

10

Frequency, GHz

Rea

lzie

d G

ain,

dB

i

Measurement0 dB



Optimization of Inverted-Hat Antenna

Inverted-Hat Antenna (IHA)

A novel compact frequency-scaled structure for broadband operation withproperly 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.





Goal: constant gain, constant impedance and uniform radiationpattern across a large BW

Approach: genetic algorithm (GA)

Design Parameters: width, global profile, curvature and # ofelliptical segments






















Cost Function

COST = αrealPreal + αimagPimag + αdirPdir + αripplePripple



Cost Function


Preal : Resistance (R) ⇒ constant

Preal =

√

1

Nf

∑

Nf

|R(f ) − avg(R(f ))|2, αreal = 0.5

Nf : total number of discrete frequencies



Cost Function


Pimag : Reactance (X) ⇒ 0

Pimag =1

Nf

∑

Nf

|X (f )|, αimag = 0.5




Cost Function


Preal : Resistance (R) ⇒ constant

Preal =

√

1

Nf

∑

Nf

|R(f ) − avg(R(f ))|2, αreal = 0.5

Pimag : Reactance (X) ⇒ 0

Pimag =1

Nf

∑

Nf

|X (f )|, αimag = 0.5




Cost Function (cont’d)






Pdir : Maximation of directivity gain (Prefer 5 dB)

Pdir = −1

Nf

∑

Nf

Pdir (f ), Pdir =

G (f ) : if G (f ) < 5 dB5 dB : else

αdir = 0.8






Pripple : Minimization of gain ripples across the band

Pripple =

√

1

Nf

∑

Nf

|G (f ) − avg(G (f ))|2, αripple = 10






Pdir : Maximation of directivity gain (Prefer 5 dB)

Pdir = −1

Nf

∑

Nf

Pdir (f ), Pdir =

G (f ) : if G (f ) < 5 dB5 dB : else

αdir = 0.8

Pripple : Minimization of gain ripples across the band

Pripple =

√

1

Nf

∑

Nf

|G (f ) − avg(G (f ))|2, αripple = 10




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

Width Global Profile Curvature # of Ellipse12” convex 0.1 33

−16 −12 −8 −4 0 4 8 12 160

2

4

6

8

10

W, in

H, i

n

Profile of 6" tall IHA

Optimized IHA using GAIHA Published by Zhao, etc. [2]

0 0.5 1 1.5 2−5

0

5

10

15

Frequency (GHz)

Dire

ctiv

ity (

dB)


0 0.5 1 1.5 2−50

−25

0

25

50

75

100

125

150

Frequency (GHz)

Impe

danc

e (Ω

)

Resistance − Optimized IHA using GAReactance − Optimized IHA using GAResistance − IHA Published by Zhao, etc. [2]Reactance − IHA Published by Zhao, etc. [2]



6” tall IHA Optimization (1 GHz - 6 GHz)

Optimized IHA using GA for constant gain and impedance

Width Global Profile Curvature # of Ellipse28” convex 0.8 31

−16 −12 −8 −4 0 4 8 12 160

2

4

6

8

10

W, in

H, i

n

Profile of 6" tall IHA


1 2 3 4 5 6−5

0

5

10

15

Frequency (GHz)

Dire

ctiv

ity (

dB)


1 2 3 4 5 6−100

−75

−50

−25

0

25

50

75

100

125

150

175

Frequency (GHz)

Impe

danc

e (Ω

)

Resistance − Optimized IHA using GAReactance − Optimized IHA using GAResistance − IHA Published by Zhao, etc. [2]Reactance − IHA Published by Zhao, etc. [2]


Concluding Remarks

Summary


Concluding Remarks

Summary

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


Concluding Remarks

Summary


Utilizing body-of-revolution (BoR) principle, compared to the commercial3-D MoM solver FEKO, the computational efficiency is improved by afactor of 100 when evaluating the performance of an electrically largedome-dipole antenna (12λ × 10λ)


Concluding Remarks

Summary


Utilizing body-of-revolution (BoR) principle, compared to the commercial3-D MoM solver FEKO, the computational efficiency is improved by afactor of 100 when evaluating the performance of an electrically largedome-dipole antenna (12λ × 10λ)

Incorporating BoR method and genetic algorithm (GA), a 6” tallinverted-hat antenna (IHA) is optimized for constant impedance and gainperformance


Documents

2010 APS_ Broadband Characteristics of A Dome Dipole Antenna