effect of antenna size on gain bandwidth
TRANSCRIPT
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Effect of antenna size on gain,bandwidth and efficiency
Ansoft Corporation
Robert Myoung
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Antenna parameter
Major Antenna parameter
Frequency Band Width
Radiation EFficiency GAin(MAX, EVERAGE)
SiZe
Trade off of major antenna parametersFBW REF GA SZ
FBW REF
[c1] GA SZ
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Size of Antenna
Definition
radius of sphere enclosing the maximum
dimension of the antenna
Size of Antenna=2a
Antenna Structure
a
Feed point
Boundary sphereTransmission Line
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Definition of Q
Definition
Definition of energy and power
Define of Fractional Bandwidth
em
rad
mme
rad
e WWP
WoWWP
WQ >>= ,2r,2
f
VSWR
2
CfLf Hf
1)/(
)/(
1
=
=
==
LH
LH
LH
HLC
ff
ff
ff
ff
f
f
BWQ
BW: Fractional bandwidth
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Minimum Q of Electrically
Small Antennas:(1/4) Spherical wave expressions
)]([1
)(cos
,)(
)(cos)1(
),()(cos
12/1
2/1
1
krrhdr
d
krPAjEE
kr
krhPnnAjEE
krhPAHH
n
n
nn
n
n
n
n
nn
n
rnr
n
nnn
n
n
==
+
==
==
nkrh
P
nP
n
n
n
orderoffunctionhankelSpherical:)(
polynomialLegendreassociatedFirst:)(cos
orderofpolynomialLegendre:)(cos1
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Minimum Q of Electrically
Small Antennas:(2/4) Non-propagation energy
[1]
[2]
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Minimum Q of Electrically Small
Antennas:(3/4)
The total radiated power
Q1, Q2, Q3,[5]
7533
53231
)(
675
)(
135
)(
216
)(18
)(63,
)(11
kakakakaQ
kakakaQ
kakaQ
+++=
++=+=
[3]
[4]
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Minimum Q of Electrically Small
Antennas :(4/4)
Meaning of Minimum Q [in case of ESA] For the any given Value of2pi*a/lambda, all Qs have different values. Hence,
the above equation can be satisfied when there is only one termunder thesummation sign. The corresponding Q of the antenna is equal to the Qn of theterm used. Since Q1 has the lowest amplitude, we conclude that the antenna
which generates a field outside the sphere corresponding to that of aninfinitesimally small dipole has potentially the broadest band width of allantennas. The gain of this antenna is 1.5
c
n kkakaBW
Q
2;
)(
1113
=+==
z
sin
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Minimum Q vs. Size of Antenna
10-2
10-1
100
101
10-1
100
101
102
10
3
Antenna size (2a/c
)
Q
PCS(15.1)CDMA(12.3)
Bluetooth(30.5)
UWB(0.764)
Target Q Antenna Size
GPS(52.5)
IEEE802.11a(26.2)
2a
Chu-Harrington limit
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Example(1/2)
Limitation of antenna Size
Type f H(GHz) f L(GHz) f C(GHz) Q 2a(mm)
GPS 1.59042 1.56042 1.57535 52.5 16.6
PCS(KOREA) 1.87 1.75 1.809 15.1 22.6
CDMA(KOREA) 0.894 0.824 0.8583 12.3 55.0
Bluetooth 2.4 2.48 2.4397 30.5 13.0
802.11a 5.35 5.15 5.2490 26.2 6.36
Ultra-Wideband
(UWB)10.6 3.1 5.73 0.764 29.0
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Example(2/2)
10-2
10-1
100
101
10-1
100
101
102
103
Antenna size (2a/c)
Q
UWB(0.764)
Bluetooth(30.5)
PCB type UWB antenna
2.4GHz
Microstrip patch antennaFR-4, rectangular type
2.4GHz Sleeve dipole antenna
35.8mm
1.5 2 2.5 3 3.51
2
3
4
5
6
7
8
9
10
Frequency (G Hz)
VSWR
55mm
1 2 3 4 5 6 7 8 9 10 11 12
0
1
2
3
4
5
6
7
8
9
10
frequency (GHz)
VSWR
VSWR, Msh3030
30mm0mm30mm0mm47mm
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Effect of Radiation Efficiency
Radiation efficiency, Q
The effect due to Bandwidth There is a possibility of getting bandwidth which is wider than
the antenna size.
lossrad
rad
accept
rad
PPP
PP
+==TRL antenna
Pin
PreflPaccept
Prad
Ploss
=+
=
+
=
QPP
P
P
WPP
WQ
lossrad
rad
rad
lossrad
2
2
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10-1 10010
-1
100
10
1
10
2
103
Antenna size (2a/c)
Q
=100%=80%=60%=40%=20%
2
0.2
0.4666
0.2100
0.1592
0.0866
Q=10 maintainingEfficiency: 100%20% decreaseSize : 0.544
Maintaining Antenna SizeEfficiency: 100%20%BW: 5
Q=1 maintaining
Efficiency 100%20% decreaseSize: 0.45
Maintaining Antenna SizeEfficiency: 100%20% decreaseBW: 5
Q vs. Size of Antenna
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Conclusion
It gives to objection smallest Q value which is existence of givenantenna size
The hazard which gets the bandwidth of the BW it stands 2aantenna space necessity of size
Effect of Radiation Efficiency Maintaining Antenna BW
Radiation Efficiency Antenna Size
Maintaining Antenna Size Radiation Efficiency BW
3
)(
111
kakaf
f
BW
Q C +=
==