harold a. wheeler’s antenna design legacy · wheeler’s formulas yield accurate values, and are...
TRANSCRIPT
Harold A. Wheeler’s Antenna Design Legacy
Alfred R. Lopez
Greenlawn, NY USA
October 24, 2007
Outline of Presentation
• Harold A Wheeler (Some Highlights)
• Harold A. Wheeler’s Antenna Design Legacy
– 1984 AP Symposium IEEE Centennial Session
“Antenna Topics in My Experience”
• Impedance matching to a transmission line
• Electrically small antenna
• Planar arrays
• Electrically Small Antenna
• Matching To A Transmission Line
• Closing Remarks
Harold A Wheeler
Harold A. Wheeler (Some Highlights)
• May 10, 1903 - April 25, 1996
• 1925 Invented automatic volume control (AVC)
• 1939 IRE Morris Liebmann Memorial Prize (paper on TV amplifiers)
• 1941 Development of mine detector used by WWII allied forces
• 1947 Started Wheeler Laboratories, inc.
• 1948 Chairman of IEEE (IRE) Long Island Section
• 1964 IEEE Medal of Honor (highest IEEE award)
• 1965-1968, Hazeltine, Chairman of the Board
• 180 US patents
• More than 90 publications over a span of 57 years
– 1928 Automatic volume control for radio receiving sets
– 1947 Fundamental limitations of small antennas
– 1975 Small antennas
– 1985 Antenna topics in my experience
Harold A. Wheeler’s Antenna Design Legacy
• 1985 AP Trans. Paper, “Antenna Topics in My Experience”(1984 AP Symposium paper not published in the Proceedings)
– Wideband Matching To A Transmission Line
• The union of antenna impedance and circuit theory
• Horizontal biconical dipole (6-18 MHz, 1936)
• Vertical Monopole on a mast (157-187 MHz, 1943)
• Impedance matching using reflection chart
– Small Antennas
• C and L of equal effective volume (1947)
• Radiation power factor proportional to volume (1947)
• Utilization of space (1975)
– Planar Arrays
• Concept of infinite array (1948)
• Relations from current sheet, scan angle (1964)
• The impedance crater (1965)
• The grating-lobe series (1965)
• Array simulators in waveguide (1963)
Small Antenna Legacy
1947 Paper: “Fundamental Limitations of Small Antennas”
(((( ))))Ab
2/6Q
3ππππλλλλππππ<<<<
Original figure appearing in Wheeler’s 1947 paper
Some Wheeler Definitions
Radianlength
The radianlength is the wavelength divided by 2π (λ/2π)
Radiansphere
The radiansphere is a sphere whose radius is the radianlength. It is
the boundary between the near field and far field of a small antenna.
Volume of radiansphere = VRS = 4/3 π (λ/2π)3
Small Antenna
“The small antenna to be considered is one whose maximum
dimension is less than the radianlength.”
“An antenna within this limit of size can be made to behave as
lumped capacitance or inductance, so this property is assumed.”
Definition of Antenna Radiation Q
Antenna Q
The ratio of 2π times the energy stored in the fields excited by the
antenna to the energy radiated and dissipated per cycle (IEEE 100)
Antenna Radiation Q
The ratio of 2π times the energy stored in the fields excited by the
antenna to the energy radiated per cycle
The antenna radiation Q is a fundamental property of an electrically
small antenna, which is inversely related to the bandwidth capability of
the antenna.
Wheeler (and) Chu Small Antenna Limitations
VolumeOccupied WheelerV
Factor VolumeEffectivek
VolumeEffectiveV
kV
V
2
9
V
V
2
9Q
Papers) 1975 and (1947 Wheeler
OC
E
OC
RS
E
RS
====
====
====
========
antenna small the
of dimension maximum
the is diameter whose
sphere of Volume
VolumeChu V
V Vfor V
VQ
Q ON BOUND LOWERQ
Paper) (1948 Chu
Chu
RSChuChu
RSChu
Chu
====
====
<<<<<<<<====
====
Wheeler’s formulas yield accurate
values, and are invaluable for the
design of small antennas.
Chu’s lower bound assumes no
stored energy within the sphere
and can only be realized in
theory. It is a very useful
theoretical reference point.
For Cylindrical Antenna: VOC = Ab
Where A = area of cylinder base and
b = height of cylinder
Wheeler’s Formula for Capacitor Antenna
material (core) fill of ypermitivit Relative
2 a
b For
1k
kk
factor Fill k
a
b41k
1 factor Shape k
factor volume Effective kk k
length dipole discs, between Distance b
radius Disc a Where
k
1k
V
V
2
9
V
V
2
9
k
1
ba
26Q
r
rSC
SCFC
FC
SC
SC
FCSCa
2SC
rSC
OC
RS
E
RS
a2
3
)(CapacitorWheeler
====εεεε
<<<<−−−−εεεε++++
≈≈≈≈
====ππππ
++++====
>>>>====
========
====
====
−−−−εεεε++++========
ππππ
ππππλλλλ
ππππ====
Validation of Wheeler’s Formula for Capacitor
1 .103
0.01 0.1100
1 .103
1 .104
1 .105
1 .106
Radiation Q
.
Disc Dipole
Computer Model
Q Versus Disc Dipole Length
Disc Radius / λ = 0.005 top, 0.01, and 0.05
(Circles are computed points)1000000
100000
Q
10000
1000
100 0.001 0.01 0.1
Disc Dipole Length / Wavelength
Wheeler’s Formula for Inductor Antenna
material (core) fill of typermeabili Relative
2 a
b For
1/1k
kk
factor Fill k
a b if value this than lessSomewhat b
a9.01k
1 factor Shape k
factor volume Effective kk k
length axial Loop b
radius Loop a Where
k
1/1k
V
V
2
9
V
V
2
9
k
1
ba
26Q
r
rSL
SLFL
FL
SL
SL
FLSLb
2SL
rSL
OC
RS
E
RS
b2
3
)Inductor(Wheeler
====µµµµ
>>>>−−−−µµµµ++++
≈≈≈≈
====
<<<<++++≈≈≈≈
>>>>====
========
====
====
−−−−µµµµ++++========
ππππ
ππππλλλλ
ππππ====
Validation of Wheeler’s Formula for Inductor
1 .103
0.01 0.110
100
1 .103
1 .104
1 .105
1 .106
Radiation Q
.
Loop Inductor
Computer Model
Q Versus Loop Axial Length
Loop Radius / λ = 0.005 top, 0.01, 0.025 and 0.05
(Circles are computed points)1000000
100000
Q
10000
1000
100
10
0.001 0.01 0.1
Loop Axial Length / Wavelength
Q Dependence on εr and µr
tyPermeabili Relative
k
1/1k
V
V
2
9Q
: AntennaInductor
yPermitivit Relative
k
1k
V
V
2
9Q
: AntennaCapacitor
r
2SL
rSL
OC
RSWheeler
r
2SC
rSC
OC
RSWheeler
====µµµµ
−−−−µµµµ++++====
====εεεε
−−−−εεεε++++====
kSC > 1
Q increases with
increasing εr
kSL > 1
Q decreases with
increasing µr
Wheeler’s Implementation of Chu’s Lower Bound on Q
mk/21
1
2
9
++++
Vr = VS
Original figure first appearing in Wheeler’s 1975 paper
Two
Typos
Optimum Shape for Cylindrical Antennas
Q Ratio = Q / QChu(Ratio of Total-
To-External
Stored Energy)
0 0.5 1 1.5 2 2.5 3 3.5 40
1
2
3
4
5
6
7
8
9
10
Cylinder Diameter to Length Ratio
.
b
D = 0.84b
Capacitor
D = Cylinder Diameter
b = Cylinder Axial Length
b
Inductor
D = 2.24b
0.84 2.24
Cylinder Diameter to Length Ratio
Optimum Spherical-Cap Dipole
Wheeler Prediction 1985: Minimum Q when cap area about ½ sphere area
Lower Bound for Q of Capacitor (Electric) Small Antennas
Area Ratio
Q
Ratio
1.75
0.44
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
1
2
3
4
5
.
.
Small Antenna Q Ratios
1.75 Spherical-Cap Dipole
2.4Disc Dipole
Diameter / Length = 0.84
4.4Cylindrical Inductor
µµµµr = 1, Diameter / Length = 2.24
3.0Spherical Inductor, µµµµr = 1
1.0Spherical Inductor, µµµµr = ∞∞∞∞
Q Ratio = Q/QChuAntenna Type
Q Ratio = Radiation Q / Chu Lower-Bound Q
It is believed that the Q for the spherical-cap dipole is the lower bound
for the Q of the capacitor (electric) antenna
“The Largest Antenna in the World is a Small Antenna”
Wheeler, 1985
Antenna located at North West
Cape, Australia
Operates at 15.5 KHz
Diameter of outer tower circle
is 1.7 miles (2.7Km)
Tower height is 1300 Ft. (390m)
Radiation Q = 435
Radiation Bandwidth = 36 Hz
Antenna Q = 116
Resonance Bandwidth = 134 Hz
Antenna Impedance
Matching Legacy
Impedance Matching
• 1935 Antenna perceived as a circuit element. Circuit theory
applied to impedance matching antenna to transmission line.
• Reflection Chart (Tool for Impedance Matching)
– 1936 Paper “Doublet antennas and transmission lines” (Reflection
chart on resistance and reactance coordinates)
– 1940 Hemisphere Reflection Charts (Smith, Carter and Wheeler)
– Wheeler developed the art of impedance matching using the
reflection chart as the primary tool (Smith and Carter charts were
used as under-lays for the Wheeler reflection chart in graphical
solutions to impedance matching problems)
• Equations for optimum impedance matching of single-tuned
and double-tuned antennas
Antenna Bandwidth Definitions
Antenna Bandwidth (Ratio) = 1/Q = (fH – fL)/f0= Antenna 3 dB Bandwidth
= Antenna Resonance Bandwidth
For an antenna tuned to resonance, fH and fL are the high and
low frequencies where the magnitude of the reactance is
equal to the resistance (f0 is the resonant frequency)
(Impedance) Matching Bandwidth (Ratio) = B = (fH – fL)/f0
fH and fL are the high and low frequencies of a frequency band
over which a specified magnitude of reflection coefficient (or
VSWR) is not exceeded
B(ΓΓΓΓ) = f(ΓΓΓΓ)/Q where ΓΓΓΓ is the maximum reflection magnitudeMatching Factor = QB(ΓΓΓΓ) = f(ΓΓΓΓ)
LH0 fff ====
Matching Bandwidth is equal to the Antenna Bandwidth
multiplied by the Matching Factor
Multiple Tuning Impedance Matching Network
Ideal Transformer
(Adjust Impedance Level)
Tuning (n)
(3) (2) (1)
R
C1
L1
L2 C2
L3 C3
Generator Antenna
R0
332211
0
0
CL2
1
CL2
1
CL2
1f
Frequency Resonant f
ππππ====
ππππ====
ππππ====
====
Optimum Impedance Matching: Wheeler and Fano
2 and 1 n
1
2QB
n
2
n
1
====ΓΓΓΓ−−−−
ΓΓΓΓ====
∞∞∞∞====
ΓΓΓΓ====
====
−−−−
ππππ
====
........ 3 ,2 ,1n
)nacosh(
)nbcosh(
)bcosh(
)nbtanh(
)acosh(
)natanh(
)bsinh()asinh(
n2sin2
QB
Wheeler Fano
It is remarkable that the Wheeler and Fano equations are in exact
agreement (n = 1, n = 2), considering their radical difference in form.
Single Tuned n = 1
Double Tuned n = 2
Infinite Tuned n = ∞
Wheeler Single Tuning
L1
C1
R
Ideal
Impedance
Transformer
R0
Generator Antenna
.
Single Tuning Reflection Chart
Mid-Band
Match
Wheeler
Edge-Band
Minimum-ΓMatching
fH
fL
Minimum Γ
OCSC
C
L
R0R
Q = 10
B = 0.2
Single Tuning Equation
(((( ))))
1 n
1
2
1
2QB
)2/tan(1
)2/tan(2)tan(
)2/tan()sin()1)(cos(
)sin()1)(cos(
1)f(z
1)z(f
QB)tan( )QB(1R
R 1)jQB1(
R
R
)sin(j)cos()jexp(jQB1R
R
R
)f(Z)f(z
f
f
f
f
R
Lj1R
f
f
f
fLjR)f(Z
n
2
n
1
2
2
22
22
H
H
20
0
00
HH
0
L
0
H10
H
0
0
H10H
====
ΓΓΓΓ−−−−
ΓΓΓΓ====
ΓΓΓΓ−−−−
ΓΓΓΓ====
φφφφ−−−−
φφφφ====φφφφ
φφφφ====φφφφ++++++++φφφφ
φφφφ++++−−−−φφφφ====
++++
−−−−====ΓΓΓΓ
====φφφφ++++========++++
φφφφ++++φφφφ====φφφφ====++++========
−−−−
ωωωω++++====
−−−−ωωωω++++====
Wheeler Double Tuning
L1
C1
R
Ideal
Impedance
Transformer
(Set for
optimum
single-tuned
edge-band
matching)
R0
Generator Antenna
L2 C2
Double Tuning Reflection Chart
.
Parallel resonant
circuit susceptance
Wheeler
Single-tuned
Edge-Band
Minimum-ΓMatching
fH
fL
OCSC
C
L
fH
fL
R0R
Double Tuning Reflection Chart (continued)
.
Wheeler
Double-Tuned
Matching
Wheeler
Single-tuned
Edge-Band
Minimum-ΓMatching
OCSC
C
L
Γ2
Γ1
fH
fL
fH & fLf0
212
1
1
2
1
Γ=Γ
Γ=
Γ
Γ
ΓΓΓΓ1
ΓΓΓΓ2 1
Similar
Triangles
Double Tuning Reflection Chart (continued)
.
OCSC
C
L
Γ2
Double Tuning Equation
2n
1
2
-1
2QB
:Tuned Double
magnitude reflection tuned-double Maximum
magnitude reflection tuned-single Maximum
-1
2QB
:case tuned single the hStart wit
n
2
n
1
2
2
2
212
1
21
1
====
ΓΓΓΓ−−−−
ΓΓΓΓ====
ΓΓΓΓ
ΓΓΓΓ====
====ΓΓΓΓ
ΓΓΓΓ====ΓΓΓΓ
====ΓΓΓΓ
ΓΓΓΓ
ΓΓΓΓ====
QB = 2.146
a3 = 2.413
b3 = 0.678
Triple-tuned matching
(Lopez-Fano, n = 3)
QB = 2.860
Infinite-tuned matching
(Fano-Bode, n = ∞)
QB = 1.732
Double-tuned matching
(Wheeler-Fano, n = 2)
QB = 0.750
Single-tuned edge-band
matching
(Wheeler-Fano, n = 1)
QB = 0.707
Single-tuned mid-band
match
(Non Fano)
QB for
V = VSWR = 2
Impedance Matching Factor
(QB)
Impedance Matching
Circuit
Impedance Matching Formulas - Summary
V
1V
1
2QB
2
−=
Γ−
Γ=
V2
1V
1
2
1lnsinh
1QB
2
2
−=
Γ−
Γ=
Γ
=
1V1
2
1ln
2
1sinh
1QB 2 −=
Γ−Γ
=
Γ
=
−+π
=
Γ
π=
1V
1Vln
1ln
QB
Rule of thumb for maximum achievable matching bandwidth (BMaxA)
If VSWR > 2 then BMaxA ≈ VSWR / Q
Γ
−+
Γ
=1
lna
b11ln
a
1sinhb
1QB
3
3
33
Closing Remarks
• Wheeler’s Small Antenna Legacy
– Radianlength
– Radiansphere
– Small Antenna Lumped-Element Concept
– Accurate Formulas for Q of Small Antennas
– Relationship to Chu’s Lower Bound on Q of Small Antennas
• Wheeler’s Antenna Impedance Matching Legacy
– Antenna perceived as a circuit element. Circuit theory applied to
impedance matching antenna to transmission line.
– Reflection Chart (Tool for Impedance Matching)
– Simple formulas relating the Q-Bandwidth product to the maximum
reflection magnitude
– Wheeler and Fano contributions provide a complete picture of
impedance matching limitations
• Wheeler: “You should work hard to find the easy way”