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Radio Education and Research CenterRadio Education and Research Center
-- 11 --
제 5 장. Practical Antennas for Various Applications.
5-1. Small antenna.ⅰ) Electrically small antenna.ⅱ) Physically constrained antenna.ⅲ) Physically small antenna.ⅳ) Planar inverted – F antenna (PIFA).
5-2. Artistic antenna (Fractals).
5-3. 전형적인 handset antenna.
5-4. Active antenna concept- various configuration of active antennas combined with microwave integrated circuit (MIC).
5-5. Concept of Ultra Wideband (UWB) Antenna.
5-6. Case study – AM 수신용 안테나의 대표적인 예로서의 Ferrite loaded loop (coil) antenna.
목 차
Radio Education and Research CenterRadio Education and Research Center
-- 22 --
5-7. Case study – GPS (Global Positioning System)용 antenna.
5-8. Multi-band antenna.
5-9. Internal antenna.
Radio Education and Research CenterRadio Education and Research Center
-- 33 --
5-1. Small antenna concept small antenna에 대한 다양한 definitions ;
ⅰ) Electrically small antenna
Antenna volume that can be physically bounded by a sphere having radius equal to 2λπ
2λπ
: radian sphere ( = 0.16 ) λ
General description for the electrical small antennas,
; 안테나의 size가 파장에 비하여 상당히 작게 되면 안테나의 복사저항 이 매우 작게 되고
상대적으로 reactance 가 매우 커지게 된다.
rR
X
→ ∴ 안테나 근처에서는 reactive stored energy가 dominant 한 반면, 안테나로부터의 거리가 증가함에
따라 reactive stored energy는 격감하고 radiated energy가 우세(dominant)하게 된다.(양은작지만).
→ (radian sphere)는 이러한 두 영역의 개념적 경계의 의미를 지닌다. (Harold Wheeler) 2λπ
→ small antenna (소형안테나)는 상술한 바와같이 복사저항 이 매우 작기 때문에 radiation
efficiency 가 매우 작다.
rR
0
1k
= ; 파수의 역수.
RE
Radio Education and Research CenterRadio Education and Research Center
-- 44 --
1rr L
RRER R
=
Radio Education and Research CenterRadio Education and Research Center
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note) 0energy stored per unit time center frequency .energy lost per unit time bandwidthr L
fXQR R BW
= = = =+
인 경우, 0LR = ( ) ( ) ( )
3
3 31 1 1
2 22r
XQR PF r rr λ
λπ ππ λ
⎛ ⎞= = = = =⎜ ⎟⎝ ⎠ ⎡ ⎤⎣ ⎦
(여기에서 ) rrλ λ
=
→ 안테나 size가 작아질수록 값 증가.-뒤에 6장의 Chu 논문 다루면서 논의.Q
Electrically small antennas의 예
; short monopole antenna, small genetic algorithm antenna, small series-tuned loop antenna.
(a) Stub (short vertical monopole) antenna of height ,20hλ=
(b) Genetic algorithm antenna of height ,25hλ=
(c) Resonant series-tuned loop antenna of height ,25hλ=
( )a( )b ( )c
20h λ= 25h λ=I
0I1rR = Ω 1.4rR = Ω 0.2rR = Ω
(전류분포)
C
Radio Education and Research CenterRadio Education and Research Center
-- 66 --
- For the short vertical monopole antenna of height , the radiation resistance is, 20
h λ=
from the22
400 1600 ePrhhR
λ λ⎛ ⎞⎛ ⎞= =⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠
where physical height [m] , effective height [m] Ph = eh = 2ph=2 21400 400 1
20p
rh
Rλ
⎛ ⎞ ⎛ ⎞= = = Ω⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠
If the height is reduced to , but the current is uniform instead of tapered as shown
in the figure below,2 211600 1600 1
40e
rhRλ
⎛ ⎞ ⎛ ⎞= = = Ω⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠
I40λ
- A resonant 10-segment genetic algorithm antenna with has a radiation resistance 25
h λ=
1.4 .rR = Ω [ E. Altshululer et al, “The significance of Genetic representation in geneticantenna design,” Proc. AP symposium, PP. 149-152, 2003. ].
20λ
40λ
0I
note) 전류가 로서 일정하다고하고 전체면적이 같도록 선택한높이 를 라 한다.
0I
( / 40)λ eh
Radio Education and Research CenterRadio Education and Research Center
-- 77 --
- A resonant series-tuned LC circuit acting as a small loop antenna of height is
analogous to the 10-segment genetic algorithm antenna.
( 2)25
h nλ= =
2
231200 ,rnARλ
⎛ ⎞= ⎜ ⎟⎝ ⎠
for diameter ,25
D λ=
2 222 231200 2 31200 0.2 .
2 2500rDR ππ λ
⎡ ⎤ ⎛ ⎞⎛ ⎞= ⋅ = = Ω⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎢ ⎥⎣ ⎦
n A
Radio Education and Research CenterRadio Education and Research Center
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ⅱ) Physically constrained antenna
; is not necessarily electrically small but is shaped in such a way that considerable sizereduction is achieved in one plane.
ex) conformal antennas – microstrip antenna.
a
b'x
'y
feed point
GND plane
t
h Dielectric substrate
GND plane(conductor)
SMA connector
Rectangular microstrip antenna geometry.
Wrapped to shape
D
Wrapped on missile
L Dπ=
w
feed points input
Microstripradiator
Feed network
Microstrip wraparound antenna on the missile surface.
( ', ')x y
Radio Education and Research CenterRadio Education and Research Center
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ⅲ) Physically small antennas
- May not fall into any of the above categories ( electrically small & physically
constrained ) yet their dimensions are regarded as small in relative sense.
A millimeter-wave horn antenna or exponential notch antenna is an example.
0λConductor
Thickness exaggerated
dielectric0 2λ
Feed strip 50Ω
-Exponential notch antenna with microstrip feed.50Ω
a
'aSectionthrough 'a a−
Radio Education and Research CenterRadio Education and Research Center
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ⅳ) Planar inverted-F antenna ( PIFA )
As a small antenna developed for the further miniaturization of portable telephone set
→ small & low profile structure.
Structure of the planar inverted-F antenna- PIFA의 개념적 구성.
1 2, , , ,L L W F h 등을 가변하여 원하고자 하는 특성(패턴이나 임피던스 등)을 구현할 수 있다.
patch
substrateconducting ground plane
patch
L
Coaxial feedResonant mode field configuration
Field configuration
Electric wall
t
2L
Miniaturization by half.
2L2L
W F
2 dΔ
hPlanar element
Short-circuit plate
Ground plane ⇐
TEM Transmission line
patch의 중심부에electric wall.
t
⇓
Radio Education and Research CenterRadio Education and Research Center
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5-2. Artistic antennas ( Fractals )
Extracted from “Antennas” by Kraus. 3rd ed. pp. 772-774.
Fractals ; structures that preserve their shape at different scales.
a) Sierpinsky – triangle bow-tie antenna
b) Barnsley – Fern dipole antenna
c) Promethea moth antenna
Artistic antennas (fractals)
Sierpinsky-triangle bow-tie antenna
Radio Education and Research CenterRadio Education and Research Center
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-Similar to a twin log-periodic antenna with elements that are like folded dipoles
- The self repeating different-size structure of a log-periodic antenna qualifies it as a fractal form.
Barnsley-fern dipole antenna
Bipectinate antennas of promethea moth
An example of many insect antenna that look like radio antenna
Radio Education and Research CenterRadio Education and Research Center
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5 GHz1 GHz
300 MHz500 MHz
3 GHz
2VSWR =
2 GHz
9cm
Coax connector
Solid plate
VSWR approximately 2 or
less from 2 to 5 GHz.
Impedance curve has 2
loops.
Impedance variation of two Minkowski fractals, a solid plate and square loop.
2VSWR =
2 GHz
3 GHz
500 MHz1 GHz
300 MHz
5 GHz
wire
Square loop
radials
More impedance
fluctuation than for plate
with curve making
3 loops close to
resonance.
Radio Education and Research CenterRadio Education and Research Center
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5 GHz
1 GHz
300 MHz500 MHz
2VSWR =
2.5 GHz
Still more impedance
fluctuation from non-
resonant to resonant
conditions making 4
loops.
wire
Minkowskifirst iteration
20 sides
2VSWR =
500 MHz 300 MHz
3 GHz2.5 GHz
Large impedance
fluctuations making 6
loops with 2 frequencies,
650MHz and 2.5GHz,
very close to resonance.
Minkowskisecond iteration wire
100 sides
Impedance variation with respect to for flat plate, square wire loop and Minkowski
fractals of first and second iteration. Note the extreme impedance fluctuations of the fractal
antennas compared with the plate and square loop. The two radials are 17cm overall.
50Ω
Radio Education and Research CenterRadio Education and Research Center
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5-3. 전형적인 handset antenna
- 전형적인 cellular handset 의 체적은 100 보다 작으며 따라서 안테나의 체적은 5
이하로 설계된다. 800MHz~900MHz 대역에서 이러한 공간적 제약 때문에 안테나자체 만으로
system bandwidth 10%를 구현하기 어렵다.
3cm 3cm
→ 그러나 실질적으로는 handset chassis에도 유기전류가 흐르기 때문에 안테나 구조 자체뿐
만 아니라 handset chassis도 복사구조를 이루고 있다.
안테나 자체가 소형이어야 하면서도 요구되는 system bandwidth 때문에 retractable whip
antenna 형태가 선호되기도 한다.
Radio Education and Research CenterRadio Education and Research Center
-- 1616 --
Review on the helical antenna.
Surface of imaginaryhelix cylinder
D
S
d L
A
helixaxis
axialmode
normalmode
normalmode
Helix and its dimension
C Dπ=
S
Lα pitch
angle
: spacing between turns
(center to center)
: length of 1 trun
: Circumference of helix =
S
LC Dπ
Radio Education and Research CenterRadio Education and Research Center
-- 1717 --
- the retractable whip antenna is typical on
handsets.
- whip 길이는 또는 . 4λ 3 8λ
- chassis 와 monopole 안테나가
unsymmetrical dipole을 구성 (∵ chassis가
finite ground plane을 구성한다고 보자).
Dual frequency normal mode helix
2λ dipole retracted
2λ dipole extended
(a) (b)
(a) handset with dual frequencynormal-mode helix and
dipole extracted/ 2λ −
(b) handset with dipole extracted.
/ 2λ −
note) whip이 retracted 된 경우, normal mode helical antenna가 안테나 역할을 take over 하는데이 경우 Helical의 pitch angle을 두 종류로 사용하여 dual band operation을 구현 할 수 있다.
Radio Education and Research CenterRadio Education and Research Center
-- 1818 --
Internal antenna (Intenna)
내장형 안테나의 두 종류;
ⅰ) planar antenna (ex. PIFA)
ⅱ) chip antenna – circuit board에 장착
Possible internal antenna.
Typical design example 8xL λ= 또는 ,
4 4yLλ λ= 또는 ,
8 4zLλ λ= 또는 , 0.14
8lλ λ=
0.092 , 0.037W hλ λ= =
Note) meander type을 채택하거나 high permittivity를 사용하여 miniaturization.
→ 성능이 다소 열화되는데 특히 body effect에 민감한 경향.
zL
yL xL
l
W
feed
groundground
feed point
chassisPIFA Meander type antenna
h
coaxial cable
planar internal multiband antenna.
Radio Education and Research CenterRadio Education and Research Center
-- 1919 --
5-4. Active antenna concept.
개요 ; 마이크로 스트립 회로와 마이크로 스트립 패치 안테나의 integration 결과, integrated circuit-
antenna module 형태가 점차 보편화 됨에 따라 active antenna 개념이 널리 사용되기 시작.
- Microwave integrated circuit + antenna
integration
Integrated (active) antenna.
- Motivation
ⅰ) Reduction in substrate area and consequently, the size
ⅱ) Elimination of interconnect lines and connectors,
ⅲ) performance enhancement of combined circuit-antenna components.
ⅳ) power combining.
ⅴ) potential cost reduction.
Radio Education and Research CenterRadio Education and Research Center
-- 2020 --
- Configurations for active microstrip patches.
ⅰ) circuits and radiators side-by-side on a substrate.
-The simplest approach to integrating circuits and antennas → to locate them on a
single common substrate.
- The selection of the single substrate needs some compromise.
∵ thick substrate with a low dielectric constant for patch antenna application
↔ thinner substrate with a higher value of dielectric constant for circuit design.
ex) The configuration where the radiating element and the circuit need to be designed together.
note) The patch acts as a radiator as well as a two-port resonator placed in the feedback loopof the FET circuit.
patch antenna
Tuning stubs
DC bias
50Ω
z
Ref : K. Chang, et al., Electronics Letters,
1988, vol. 24, no. 21, pp. 1347-1348.
An oscillator with a radiating patch in the
feed back loop
FET
Radio Education and Research CenterRadio Education and Research Center
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ⅱ) Devices integrated on/under radiating patch.
- 이 경우에 active device(능동소자)는 patch면이나 patch 아래의 substrate에 장착(위치)된다.
→ 패치내의 field와 소자관련 field 간에 강한 interaction.
- 다양한 형태의 diode (Gunn, Impatt, Varacter)를 사용한 oscillator-antenna configurations.
A typical configuration of a diode located underneath the patch ;
note) Varactor diode의 경우에도 이러한 configuration이 사용될 수 있다. 이 경우 DC bias에 변화를
주어 operating frequency를 변화할 수 있어야 한다.
Radiating patch
Gunn diode
Heat sink
Gunn diode
DC bias line
b
a
( ),g gx yA generic configuration for integrating diodes with a radiating patch.
mount
Radio Education and Research CenterRadio Education and Research Center
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MESFET의 경우, microstrip patch와의 integration이 가능한 configuration의 일례 ;
ⅲ) Circuits below the ground plane of the patch.
- In this configuration for active microstrip antennas, the circuit functions are located onthe back side of the ground plane.the output of the circuit portion is coupled to the patch, either via a slot in the groundplane or via a probe running through a hole in the metalization of the ground plane.
Drain lead soldered to patch
Narrow slot for feedback capacitance and bias isolation
Dielectric substrate
Quarter-wave stub, shorted to ground
Gate lead soldered to patchSource lead, solderedto ground plane
Drain bias
RF bypass capacitor
Ref : R. York, et al., Electronics letters, vol. 26, no. 7, 1990, pp. 494-495.
An arrangement for integrating a MESFET with a radiating patch
PackagedMicrowave FET.
note) The source leads are soldered to the earth plane through the substrate ;they do not make contact with the gate side of the patch.
Radio Education and Research CenterRadio Education and Research Center
-- 2323 --
Simple example)
한 예로서 아래 그림과 같은 aperture-coupled microstrip patch antenna의 경우 위층 기판에서
의 antenna부의 설계와, 아랫층의 급전 회로부 설계가 서로 독립적으로 이루어질 수 있다는 것이
큰 장점이다. 물론 ground plane 에서의 slot을 통한 coupling 부를 제외하고.
이러한 형태의 안테나는 two-layer이기 때문에 한 예로서, millimeter wave monolithic phased
array를 설계하는 경우, phase shifter와 amplifier와 같은 active device는 아래층의 gallium arsenide
기판을 사용하고, 안테나부는 상대적으로 낮은 을 갖는 위층 기판을 사용할 수 있고, 이 때문에 능동
소자나 급전선으로부터의 spurious radiation을 줄일 수 있다는 장점도 있다.
이러한 aperture-coupled microstrip antenna 구조를 이용하여 feedline 이 위치한 기판에 circuitry
를 꾸미면 다음과 같이 two-port active coupled microstrip antenna를 설계할 수가 있다.
Mircostrip patch
feedline
Conducting plane
Ground planewith aperturesuch asnarrow slot.
Aperture –coupled microstrip patch antenna.
bd
ad
brε
arε
rε
Radio Education and Research CenterRadio Education and Research Center
-- 2424 --
ⅳ) configuration for active antennas using slot radiators.
- 앞에서 논의한 microstrip patch를 복사소자로 사용하는 대신, slot형태 (slot, folded slot,
tapered slot 등)을 복사소자로 사용하는 경우, 대부분 coplanar waveguide (CPW)로 급전을
하고, FET와 같은 능동소자도 바로 CPW상에 장착되는 구조를 취한다.
patch
slotted ground plane
microstripline
slot
port 4 port 3
port 2port 1
stubs
four-port module
active element
1
23
4
( )a ( )bFour-port structure and geometry : (a) slot length : 11mm, slot width : 1.6mm, patch length : 40mm,
patch width : 30mm, (b) schcmatic arrangement of suggested applications.
slot
slot
Radio Education and Research CenterRadio Education and Research Center
-- 2525 --
한 예로서 compact wideband integrated active slot antenna amplifier 구조를 도시하였다.
- FET amplifier와 tapered slot antenna를 integrated한 형태
- and are closen to accomplish the impedance
matching to the antenna.
2L 3L
Circuit configuration of CPW cross-feed linear tapered slot antenna amplifier.
DC block
1S Source2S
drain
.FET amplifier
1L
gate
2L3L
H
W
tapered slot
conductor
Radio Education and Research CenterRadio Education and Research Center
-- 2626 --
- Design approaches for active microstrip patches
; Full-wave numerical simulation of active patches.
- Most simulations include ;
integral equation based moment method analysis both in spectral domain and in
space domain, FDTD(finite difference time domain) simulation and FEM(finite
element method) etc.
- Integral equation based simulation of microstrip patch antenna is modified to
incorporate lumped active or passive components
→ key ingredient in the analysis of the circuit – antenna module
EM simulator + SPICE
MoM, FDTD, FEM, etc.
Radio Education and Research CenterRadio Education and Research Center
-- 2727 --
Synopsis:
- UWB antenna : specially designed to transmit and/or receive very short time duration of
electromagnetic energy.
-UWB antenna design remains the major factor in the progress of UWB technology.
-This section describes a study of conventional antennas and why they are not suitable for a
UWB system.
Introduction
UWB technology ; based on the use of very narrow pulses on the order of nanoseconds, which
covers a very wide bandwidth in the frequency domain.
(Now an important hot topic in industry and academia)
resonant type(such as -dipole antenna.)-standing wave type.
nonresonant type-travelling wave type.
Classification of antennas. ;
2λ
5-5. Concept of Ultra Wideband (UWB) Antenna
Radio Education and Research CenterRadio Education and Research Center
-- 2828 --
resonant type
; resonant frequency, very narrow bandwidth.
nonresonant type
; broad bandwidth, large physical size(so inappropriate for portable UWB devices).
Frequency characteristics :
( , .)2
ex dipole antλ −
Radio Education and Research CenterRadio Education and Research Center
-- 2929 --
i) Resonant antennas.
- The most common and easiest antennas for communications are wire antennas.
One of the simplest representative antennas is the dipole antennas.
inefficient radiator due to small radiation
(very small radiation resistance).
dipole resonant antenna was a solution
to the inefficiency of the Hertzian dipole.2
λ −
Hertzian dipole as a radiating element.
note) Charge accumulation by a uniform
current at both ends of the dipole.I
P
r
y
z
x 0 cosI I tω=
lΔ
θ
, ,l I uniform along length lλΔ
Radio Education and Research CenterRadio Education and Research Center
-- 3030 --
0'
',( , ) ' ,
4v
rJ r tcA r t dv R r r
Rμπ
⎛ ⎞−⎜ ⎟⎝ ⎠ ′= = −∫
note) 에서 은 time retardation을 의미.rtc
−rc
resonant dipole antenna.2λ−
- Sinusoidal current distribution → resonant current distribution.
- Radiating current can be made to be significantly increased by use of the resonance
phenomena – RLC equivalent circuit analogy.
- Sinusoidal current distribution(like a guitar string)
; resonance(=standing wave current)
→ very narrow bandwidth radiator.
source
θ
I
r
sinusoidal currentdistribution.
z
물론 윗 식에서 은 인 체적을 의미.'v 0J ≠
관찰점 P( , ).A r t
'v
Radio Education and Research CenterRadio Education and Research Center
-- 3131 --
If an impulse of UWB is fed to
such a resonant antenna(having
very narrow bandwidth), a ringing
effect will occur as shown in the
figure.
resonant dipole antenna2λ−
t
radiated wave
having narrow bandwidth.
verynarrow pulse.
Radio Education and Research CenterRadio Education and Research Center
-- 3232 --
ii) Nonresonant antennas.
Nonresonant or frequency-independent (FI) antenna
; an antenna designed to have approximately constant input impedance and radiation
characteristics over a wide range of frequencies.
→ the maximum dimension of this kind of antenna is set by the lower frequency limit.
Wideband antenna
; If the impedance and radiation characteristic of an antenna do not change significantly over
about an octave or more.
Examples of the wideband antenna ; log-periodic antenna and spiral antenna.
Radio Education and Research CenterRadio Education and Research Center
-- 3333 --
A log-periodic dipole antenna. The basic arrangement of a
spiral antenna.
Feedpoint
Feed point
Radio Education and Research CenterRadio Education and Research Center
-- 3434 --
- Basic principle of original spiral antenna.
An (infinite) equiangular spiral antenna structure.
1ake ψρ =
( )2
ake ψ δρ −=
( )3
ake ψ πρ −=
( )4
ake ψ π δρ − −=
- V. H. Rumsey proposed that a structure which could be defined entirely by angles(without any
characteristic length dimension) should have characteristics that are independent of frequency.
However these antennas(LP&spiral ant.) are likely to be dispersive and inappropriate for short(UWB) pulses.
They radiate different frequency component from different parts of the antennas.
→ So the radiated waveform will be extended and distorted.
In essence, a trade-off is necessary to obtain an efficient, electrically small antenna suitable for the
UWB application.
conductor
Radio Education and Research CenterRadio Education and Research Center
-- 3535 --
iii) The UWB Antennas;
UWB → short-range wireless communication (making use of data transmission in
the 3.1-10.6GHz).
→ different from a traditional carrier wave system (A UWB system sends very low power
pulses, below the transmission noise threshold.
The antennas in UWB communications = significant pulse shaping filters
∴ 주파수 영역에서의 filtering에 의한 신호왜곡에 의하여 송출된 pulse shape의 왜곡이 초래되므로
수신기에서의 detection mechanism의 복잡도가 증대.
Requirements for UWB antenna;
; phase center와 VSWR가 동작주파수대 전체에 걸쳐 일정해야,
→ 주파수에 따라 phase center가 변하면, transmitted pulse의 왜곡에 의하여 수신단에서의
성능 열화가 초래된다.
∴ 저가, 소형이면서 복사효율면에서 좋은 UWB 안테나 design이 관건.
Radio Education and Research CenterRadio Education and Research Center
-- 3636 --
Antenna Design example for the UWB communication.
A prototype of a thin and small antenna on FR-4 substrate.
이고 substrate height 인 FR-4기판에 설계 제작된 UWB용 안테나의 design
example.[K. Y. Yazdandoost et.al “UWB antenna” IEEE Radio Communications, pp.529-532,
June 2004].
4.4rε = 0.5h mm=
4cm
Radio Education and Research CenterRadio Education and Research Center
-- 3737 --
설계된 안테나의 wideband mechanism은 아래그림에서와 같이, 가장 낮은 동작주파수에서 양단의
(two arm) 등가회로가 LC회로로 주어지고, 급전전류가 정해진다. 주파수가 높아지면서 급전부 주위
의 전류밀도가 가장 크며 가장 자리로 갈수록 그 크기가 작아진다.
이러한 결과로서 광대역 특성이 얻어진다.
또한 VSWR
Radio Education and Research CenterRadio Education and Research Center
-- 3838 --
- Camcorder와 같은 제품의 경우와 같이 소형의 UWB 안테나 설계를 위하여 적절한 구조를 갖는
chip 형태의 design도 가능하다.
7
6
5
4
3
2
13 4 5 6 7 8 9 10 11
( ).Frequency GHz
The VSWR of the proposed antenna.
Radio Education and Research CenterRadio Education and Research Center
-- 3939 --
5-6. Case study – AM 수신용 안테나의 대표적인 예로서의 Ferrite loaded loop(or coil) antenna
- AM 수신용의 실제적인 example
Review) 반경이 인 one-turn loop 안테나의 경우, 반경 가 파장 에 비하여 충분히 작은 경우,
input port 에서 복사구조 쪽으로 바라다
본 복사저항 ;
kk ′−
rR ( )4220 λπ PRr =
, 여기에서 2P aπ=
참조 ; 안테나공학 Ⅰ 제 3장 5절
0I
0I0Ik k′
a
a a λ
안테나공학 Ⅱ 제 1장 5절
: effective aperture area 개념과 Thevenin
circuit theory; Case study – receiving
properties of a small loop antenna.
Radio Education and Research CenterRadio Education and Research Center
-- 4040 --
ⅰ) 실제 도선에서 skin effect에 의한 ohmic loss를 고려.
skin depth 여기에서σμπδ f1= ,][Hzfrequencyf =
,][ 1−= Hmmediumoftypermeabiliμ 1[ ]conductivity of medium mδ −=
확대0I
0I0Ik k′
Loop ant.의전체길이 P
δ
d
( )
( )2
( )2
1
dr
dr
J
J e
δ= −
== ⋅
Review)
lR P dσ π δ=
: 도선 단면적에서 전류가 흐르는 면적
(skin depth ⅹ 도선 단면의 원주에 해당)
( )S dπ δ=
Sσ
( 2 )L aπ=
저항 ,R L Sσ=
2 aπ=:a Loop의 반경
도선의cross section
; 도선의 직경d
2 .P aπ=, 여기에서
여기에서 : 매질의 전도도.σ
r
2dr δ= −
2dr =
도선
도선의 단면
Radio Education and Research CenterRadio Education and Research Center
-- 4141 --
∴ Ohmic (loss) resistance ;lR
( )0
1l
fP P PRd dd f
μσπ δ πσσπ π σμ
= = = , where (도체에서의 투자율) 0μμ =
일반적으로 직경 이 파장에 비하여 충분히 작은 loop antenna의 경우, 커다란
Inductance 값을 지니고 있다. 그런데 이러한 inductance에 의한 reactance가
capacitor를 부가하여 상쇄된 경우로 가정하면,
( )a2
k k′lR
rR
1
j L
j C
ω
ω
lRrR
k k′
I
tR
에서의 terminal impedance 는 실수부로서 로서 주어진다.kk ′− tR t r lR R R= +
δ
2 ( )p aπ= 원주
inZ
a
2p aπ=원주:
Remind ! 안테나 공학 Ⅱ의 제 1장 5절의 case study-receiving properties of a small loop antenna 참조.
; port에 C (커패시터)를 연결하여 공진시키고, 이러한 공진 주파수에서의 을부하쪽으로 matching시켜준다는 사실을 기억하자.
kk ′− 2 ( )in r lZ Q R R= +
( )L=
Radio Education and Research CenterRadio Education and Research Center
-- 4242 --
- 이러한 경우, 복사효율 (radiation efficiency ).k rad ia ted pow erinpu t pow er
( ) ( )2
21 ,
1r r
r l l rr l
I R RkR R R RI R R
= = =+ ++
여기에서 one-turn loop 안테나의 경우,
( )( )
( )( ) 52
04
533420
420
201
2020 ⋅⋅ ⋅⋅
⋅===π
σμπ
πσμλππσμ c
dfPcfPfdP
PfdP
RR
r
l
( )( ) ( )3 5 46 8 7 7
3 5 2 53 6
10 3 10 4 10 5 .7 101 .2010
l
r
RR P f d
π
π
− ⋅ −
⋅ ⋅
⋅ × ⋅ × ×= ⋅
⋅ ⋅
Cu의 경우, 을 사용!7 1 7 1
05 .7 10 [ ] , 4 10 [ ]C u m H mσ μ π− − −= × = ×
⎥⎦
⎤⎢⎣
⎡=
fcλ
3441.0287=
Radio Education and Research CenterRadio Education and Research Center
-- 4343 --
( )3.533441l
r MHz
RR P f d
∴ =⋅ ⋅
여기에서 loop의 원주 (circumference), P = 2 , [ ]a mπ
f = frequency [ ] ,MHz
d = loop wire (conductor) diameter [ ] ,m
Radio Education and Research CenterRadio Education and Research Center
-- 4444 --
a) at lMHz
( )3.5 3 3.5 233441 3441 11097.753
10 10l
r MHz
RR P f d π −
= = =⋅ ⋅⋅ ⋅
∴ radiation efficiency
( )1 1 0.0000901 [ 40.45274186 ]
1 1 11097.753l rk dB
R R= = = −
+ +
b) at l0MHz
( ) ( )3 3.5 23441 3.509417639 ,10 10
l
r
RR π −
= =⋅ ⋅
ex) 직경 d=10mm인 도선으로 loop ant.(루프 직경이 1m인)를 제작했을 때
a) 1MHz 와 b) 10MHz에서의 복사효율 ;
Solution)
∴ radiation efficiency
( )1 1 0.221758124. [ 6.54120461 ]
1 1 3.509417639l rk dB
R R= = = −
+ +
Radio Education and Research CenterRadio Education and Research Center
-- 4545 --
Radiation efficiency factor versus frequency.
For a 1m diameter single-turn
copper loop in air.
( )[ ] , 10[ ] ,P m d mmπ= =
Note ; 작은 loop 안테나는 낮은 복사효율에도 불구하고, (signal-to-noise)
ratio가 acceptable하면 수신용 안테나로의 응용 범위가 넓다.
S N
frequency, [MHz]
0.1 101
Radiation
efficiency
factor,
dB down
k
80
60
40
20
0
40.45 [ ]dB−
복사 효율이 0.06%보다도 떨어지는 안테나라도 S/N비만 괜찮으면 수신용으로 사용될 수 있는데
저가의 AM 수신용 안테나나 Pager의 안테나가 이에 속한다.
Radio Education and Research CenterRadio Education and Research Center
-- 4646 --
- Multiturn loop antenna의 경우,
; N-turn loop에서 도선을 따라 전류분포가 균일
한 경우, far field region에서의 복사전계 또는
복사자계는 배가 되므로 복사전력은 으로
증가하므로 인데 반하여 의 경우,
전체 loop의 길이 (즉 에 비례).
n 2n2nRr ∝ lR
∝lR
( ) dnfPRR
MHzr
l
⋅⋅=∴ ⋅533
3441
→ approximate expression valid for sufficient spacing between adjacent turns and few turns
in number.
(∵ 각 turn간의 stray capacitance effect 무시)
x
y
z
2-turn의 경우
.n∝ n
2nn
Radio Education and Research CenterRadio Education and Research Center
-- 4747 --
- Ferrite rod antenna.
; multiturn loop 또는 coil 안테나의 경우, ferrite rod를 도입함으로써 복사효율을 증대.
: DC bias 차단용의 by-pass condenser, 0C
1C : turn수와 으로서 공진주파수 미세조정, 즉 공진용. 1C
ln turns
Area aFerrite rod
Magnetic field line
Mixer IF out
Receiving vertical polarization
(electric field 기준)
Magnetic field
electric field
MixerIF
BPFBlock diagram
LO
LO
0C1C
여기에서
Radio Education and Research CenterRadio Education and Research Center
-- 4848 --
Note ; coil의 역할
; antenna 구실 뿐만 아니라 과 함께 공진회로(resonant circuit)를 구성, 즉
broadcast receiver(500kHz~1600kHz)의 first(mixer) stage의 공진회로를 구성.
1C
- Ferrite가 도입된 경우, 즉 ferrite rod 안테나의 복사저항에 대한 논의 ;
먼저 ferrite가 사용되지 않는, 원래 single turn loop 안테나의 경우,
( ) ( )242 2 2 220 20rR P Pπ λ π λ→ = =
Again, 1-turn loop ant. without ferrite rod의 경우,
( ) ( )2 4 42
231200 20 197 .r A P PR π λ λλ⎛ ⎞= = ⋅ = ⋅⎜ ⎟⎝ ⎠
⇒ Multiturn 즉 n-turn의 경우,
( )2 42 2
231200 197 .r A PR n n λλ⎛ ⎞= ⋅ = ⋅⎜ ⎟⎝ ⎠
( ) ( )2 22 2 2 2 220 4 20 16A Aπ π λ π π λ= = ⋅ ⋅ 2P aπ=2A aπ=
2 2 24 4P a Aπ π∴ = =
loop의 반경.
.
∵
2 2 2 231200 20 16A Aπ π= ⋅∵2 420 Pπ= ⋅
( ) ( )22 24 A Pπ⎡ ⎤=⎢ ⎥⎣ ⎦∵
(loop의 면적)
Radio Education and Research CenterRadio Education and Research Center
-- 4949 --
⇒ Ferrite loaded loop (Ferrite-rod ant.)의 경우,
( ) ( ) ( ) ( ) [ ]2 42 22 2231200 197r er erA PR n nμ μ λλ= ⋅ ⋅ = ⋅ ⋅ Ω이 경우 Ferrite rod에 의한 손실저항(loss resistance);
( ) ( )20 02 ,rf err
aR f n lμπ μ μμ′′= ⋅ ⋅ ⋅ ⋅′
여기에서 , [ ]f frequency Hz=
,er effective relative permeability of ferrite rod dimensionlessμ =
' ,r real part of relitive permeability of ferrite material dimensionlessμ ='' ,r imaginary part of relative permeability of ferrite material dimensionlessμ =
7 10 4 10 , [ ]Hmμ π
− −= ×
n number of turns=2sec , [ ]a ferrite rod cross tional area m= −
, [ ].l length of ferrite rod m=
; 안테나 공학 Ⅱ 제 1장 6절 Case
study-ferrite core loop antenna
(자성체의 효과) 참조.
Radio Education and Research CenterRadio Education and Research Center
-- 5050 --
Note ; ring과 같은 closed 형태와는 달리, ferrite rod와 같은 open 형태의 경우,
r erμ μ> (due to demagnetization effect)
ex) For a rod of length-diameter ratio of 10, 250 50.r erμ μ= > =
∴ Ferrite rod ant.의 경우, radiation efficiency factor ,k
( )1
1
r
r l f l fr
RkR R R R R
R
= =+ + ⎡ ⎤+
+ ⎢ ⎥⎢ ⎥⎣ ⎦
또한 Ferrite rod ant.의 total resistance인 로 부터 와 (bandwidth); r l fR R R+ +
0 0 02 ,r l f r l f
L f L fQR R R R R R BW
ω π= = =
+ + + +
여기에서 0 , [ ]f center frequency Hz=
20( ) , [ ]er n aL inductance H
lμ μ⋅ ⋅ ⋅
= =
, [ ]BW bandwidth at half power Hz= −
Q BW
; 안테나 공학 Ⅱ 제 1장 5절 참조.
Radio Education and Research CenterRadio Education and Research Center
-- 5151 --
이고 으로 가정하여 1MHz에서
ex) 직경이 1cm이고 길이가 10cm인 ferrite rod에 직경이 1mm인 enameled wire로
10-turn을 감은 구조를 지닌 방송수신용 안테나(multiturn ferrite rod ant.)의 경우,
250 2.5r r rj jμ μ μ′ ′′= − = − 50erμ =
Qa) Radiation efficiency, b) , c) 를 구하는 문제; BW
먼저, ( ) [ ] [ ]4
2 2 4197 1.91 10 ,r erPR nμλ
−⎛ ⎞= ⋅ ⋅ Ω = × Ω⎜ ⎟⎝ ⎠
( ) [ ] [ ]''
202 0.31 .rf er
r
aR f nl
μπ μ μμ
⎛ ⎞ ⎛ ⎞= ⋅ ⋅ ⋅ Ω = Ω⎜ ⎟ ⎜ ⎟⎜ ⎟′ ⎝ ⎠⎝ ⎠
또한 을 사용하여[ ]51 7 10 mf
δπ σμ
−= = × [ ]( ) 0.026 .lnPR
dσπ δ= = Ω
코일원주
( )( )
4
1790
1 11790 , 5.6 101791
1
l f
r l fr
R Rk
R R RR
−+∴ = ∴ = = = ×⎡ ⎤+
+ ⎢ ⎥⎢ ⎥⎣ ⎦
; radiation efficiency.
b) 0 02 162
r l f
f L fQR R R BW
π= = =
+ +
c) 0 6.12 [ ]162fBW kHz= =
Radio Education and Research CenterRadio Education and Research Center
-- 5252 --
5-7. Case study – GPS (Global positioning system)용 안테나
-GPS; NAVSTAR GPS = Navigation System with Time and Ranging Global Positioning System.
- GPS Antenna Specification
RHCPRHCP편파편파55
3 dB max3 dB max축비축비44중심주파수중심주파수
1.5 max1.5 maxVSWRVSWR33
Return lossReturn loss
--10 dB10 dB
10 MHz min10 MHz min대역폭대역폭22
1575 MHz1575 MHz
( 3 MHZ)( 3 MHZ)
중심주파수중심주파수11
NoteNoteSpecificationSpecificationParameterParameterNo.No.
±
note) – 안테나의 형태는 무지향성.- 안테나와 수신기 접속 동축 cable에서의 감쇠 보정을 목적으로 안테나에 저잡음 증폭기 (LNA)나
주파수 변환회로 내장.
Radio Education and Research CenterRadio Education and Research Center
-- 5353 --
-GPS용 microstrip CP 안테나ⅰ) 인 직사각형 patch 공진기 내에, patch에서의 전류 분포가 서로 직교하고 위상차가 인,
두 TM mode가 여기 (excited)되도록 급전점 (feed point)을 선정하여 급전한 경우.
ⅱ) 공진기인 rectangular patch 안테나의 도체 표면에 slot과 같은 perturbation을 줌으로써, 전류분포가서로 직교하는 방향으로 흐르며, 위상차가 인 두 공진(TM) 모드를 여기하도록 한 경우.
Left-hand circular (LHC) Right-hand circular (RHC)
Single-feed arrangements for circular polarization of rectangular microstrip patch antenna.
Right-hand Left-hand
Circular polarization for square patch with thin slots on patch (c=W/2.72=L/2.72, d=c/10=W/27.2=L/27.2).
Feedpoint
Feedpoint
Squarepatch Square
patch
( , )y z′ ′ ( , )y z′ ′ LL
WW
y y
z z
L W≠ 90°
90°
W L=
W L= W L=
W L=d
dc
c
Radio Education and Research CenterRadio Education and Research Center
-- 5454 --
ⅲ) square patch 가장자리에 perturbation을 주거나 또는 타원형 patch 가장자리에 tab과 같은perturbation을 준 경우.
a
b45°
L
W
Trimmed square (L=W) Elliptical with tabs
Circular polarization by trimming opposite corners of a square patch and by making circular-patch slightly elliptical and adding tabs.
Radio Education and Research CenterRadio Education and Research Center
-- 5555 --
-Two 1/2 turn bifilar helices or one 1/2 turn quadrifilar helices for axial mode.ⅰ) Lower ends are short-circuitedⅱ) A bifilar helix end-fed by a balanced 2-wire transmission line produces a back-fire beam. →
Ref: C. C. Kilgus, IEEE. AP. Vol.17, pp.349-351, May 1969.와C. C. Kilgus, IEEE. AP. Vol.23, pp.392-397, May 1975.
4λ
4λ
0V∠ °
90V∠ °
Pattern maximum(backfire)
• 각 helix의 길이
• Lower end short-circuited
• 두 쌍의 급전 – 윗 부분에서 fed in phase quadrature
• resonant type narrow BW
2λ
Note) 각 helix의 길이를 대략 로 하고 아래 부분의 short를open 처리해도 비슷한 성능. 4
λ
→
→
Radio Education and Research CenterRadio Education and Research Center
-- 5656 --
-Forward end-fire CP용으로도 사용가능 ; 보다 큰 pitch angle을 채택함으로써.Ref. : A. A. Adams. et al., IEEE. AP. vol. 22, pp.173-178, Mar. 1974.
와 C. W. Gerst. et al., Electronics, pp.100-110,Aug.22, 1966.
- Low-gain Quadrifilar Helical Antenna (QHA)i) growing interest in simple, low-data-rate, land mobile and maritime terminals such as long-distance
trucks, cars and small ships.
- Examples of a quadrifilar helix antenna for car and truck applications.
Socket inside which the end of the four wires of QHA is short-circuited
PTFE mandrel
Small ground plane for beam shaping
• 각 helical 길이
• 각 helical의 turn수
0.5λ≅
0.5=
Radio Education and Research CenterRadio Education and Research Center
-- 5757 --
- QHA의 구동회로 구성;
2a
반사판t
G
H
d 지지대
rr
2a
Hybrid
Hybrid
90°Hybrid
90°
180°
소자 1
소자 2
소자 3
소자 4
소자 4
소자 1
소자 2
소자 3
원통봉- hybrid circuit와
hybrid circuit는microstripline으로 구현.
90°180°
090− 180−
270−
0 180−
Radio Education and Research CenterRadio Education and Research Center
-- 5858 --
4λ
4λ
0Z0Z
0Z 0Z
0Z0Z 0 / 2Z
0 / 2Z
② (Output)
③ (Output)
(Input)①
④(Isolated)
4λ
4λ
4λ
34λ
cY
cY cY
cY1Y
1θ
1θ
1θ
2 13θ θ=
①
② ③
④
Branch line coupler( hybrid circuit)90°
; 입력 단자 1로 입사된 파는
단자 2와 3으로 의
위상차를 갖고 나간다.
902π⎛ ⎞° =⎜ ⎟
⎝ ⎠
Hybrid ring (Rat-race)( hybrid circuit)180°
180°차이,; Port 1Port 2Port 4
Port 3.
Port 2 Port 4.Similarly,
×
×
Radio Education and Research CenterRadio Education and Research Center
-- 5959 --
-Low-cost quadrifilar helix antenna developed for the NAVSTAR satelliteof the Global Positioning System (GPS) ;
• broad beamwidth• minimum gain fluctuation• circular polarized radiation pattern• minimal ellipticity at low elevation angles• simple in construction• low in production cost
Note) 앞의 구조, 즉 지상차량과 위성간의 통신을 위하여 저가의 model 개발 예
feeding geometry의 단순화, 즉 1개의 hybrid와 2개의 hybrid를 사용하여 quadrifilar 4개 단자에의 위상차가 있는 신호를 보내는 대신에 두 개의 bifilar에 위상차를 갖는 신호를
보내도록 하여 단순화.
Ref. : A. Kumar, Fixed and mobile terminal antennas, pp. 183-193, Artech house, 1991.
→ 90°180°90°0, 90 , 180 , 270− ° − ° − °
Radio Education and Research CenterRadio Education and Research Center
-- 6060 --
5-8. Multi-band Antenna
- Progress in digital communication technology
- 여러 service에 할당된 주파수에 해당되는 전자파를 수신할 수 있는 multi-band 안테나의 필요성; 대표적인 multiband 안테나
PIFA, 내장형 chip 안테나, 다양한 형태의 slot 안테나 등.
• Cellular (800 MHz)• PCS (1.8 GHz)• GSM (800 MHz)• GPS (1.5 GHz)• WLAN (2.4 GHz)• Wi-Bro (2.3 GHz)
Radio Education and Research CenterRadio Education and Research Center
-- 6161 --
- 여러가지 다양한 형태의 PIFA 안테나 구조들
다양한 다중대역 또는 광대역용 PIFA의 형태.
(a) Triple band PIFA (b) Integrated PIFA (c) 기생패치 PIFA
Ground
Substrate
Feeding
Mounting
Shorting pin
Top view
Side view
parasitic
Ref. L. Economou, R. J. Langley,“Multi-band mobile telephoneantennas”,11th International conferenceon AP, no.280, pp. 754-757,2001.
Ref. A. F. Muscat, C. G. Partini,“Novel compact handset antenna”, 11th Internationalconference on AP, no.480,pp. 17-20, 2001.
Ref. Ericsson Inc, “Analysis ofintergrated inverted-Fantennas for bluetoothapplications”, antennasand propagation forwireless communications,pp. 21-24, 2000
feeding
feedingshort
Radio Education and Research CenterRadio Education and Research Center
-- 6262 --
Ref : A. F. Muscat, et al., “Novel compact handset antenna”, IEE. ICAP, pp.336-339, April 2001.
a) 이중 공진 주파수의 비 가 1.8 ~ 2.4 이며 900 MHz와 1.8 GHz, 2 GHz 대역을 동시에 수신이
가능한 PIFA 구조의 일례.
b) 소형 PCB 상에 안테나의 도체부를 pattern화하여 전체 안테나 size와 이중 주파수 대역을 만족하도록설계된 구조.
c) 광대역화를 위하여 원래의 복사구조 옆에 기생소자 (parastic element)를 추가한 경우.
2
1
ff
⎛ ⎞⎜ ⎟⎝ ⎠
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- printed monopole 형태의 multiband antenna
•Slit이 없는 경우 공진 주파수
•Tunable frequency range of
•Slit 폭 L의 변화에 대하여 첫번째 주파수의 변화는 거의•없는데 비하여 두 번째 주파수가 크게 변하는 특징
• 조정 impedance matching
1888 MHz→
2
11.37 ~ 2.05f
f⇒
sL →
Ref : Yi-Fang Lin et al., “Dual frequency coplanar triangular monopole antenna”, Proc. IEEE APSymposium. pp.48-51, 2002.
- printed multi-band antenna for 2.4 ~ 2.5 GHz WLAN and satellite DMB applications.
Coaxial feeding
A side – signal, F side – ground
Gain: 2.91 dBi for 2 GHz band4.46 dBi for 5 GHz band
12 2 7 5 2 8
8 3 12
3
3
3
Coaxial Cable50 Ω Unit : mmx
y
z
ABC
D
E
F
S
xy
z θ
φ
WL
2L0L
SL
2 mm
W1L rε
h
20 mmMicrostrip line
50 Ω
fWGround plane(bottom side)
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Ref : S. H. Hwang et al., “ A printed multi-band antenna for 2.4 ~ 2.5 GHz WLAN and satellite DMB applications”, Proc. ISAP 2005, pp.117 -120, Seoul, Korea.
Frequency [GHz]2.0 3.0 4.0 5.0 6.0
SimulationMeasurement
0
-5
-10
-15
-20
-25
-30
ReturnLoss[dB]
2.44 GHzISM Band
2.6 GHzDMB Band
5.2 GHzISM Band
5.8 GHzISM Band
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5-9. Internal Antenna (내장형 안테나)
- 발달과정
; 초기 cellular phone 시대의 retractable한 구조PCS 등 이동통신 단말기의 소형화 + Sar (Specific Absorption Rate) 개선
- Internal antenna의 종류
ⅰ) PIFA (Planar Invented F Antenna).
ⅱ) Chip antenna.
; 상대적으로 높은 유전율 (예를 들어 )로 된 chip 표면에 변형된 PIFA, Helical 또는 meander line형태의 안테나 도체를 patterning.
09ε ε=
Chip 안테나 (Bluetooth 용)의 제품 예와 헬리컬 또는 meander-line을 이용한 chip 안테나 구조.
→
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ⅲ) Branch line planar monopole 형태
이중대역이나 삼중대역 등의 구현 등 설계의 자유도가 높은 구조.
자동차의 열선 겸용 back glass antenna와 유사한 형태.
Dual band branch line planar monopole. Triple band branch line planar monopole.
Branch 1Branch 3
Branch 2
Branch 1
Branch 2
급전부급전부
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ⅳ) Fractal antenna- 광대역, 다중 대역, 소형화 가능성
Note) ⅰ) 소형화, 다기능화 등 휴대의 편리성이 요구되는 추세에서 (단말기 형태 design 의 아름다움 포함)내장형 안테나 수요 탄생.
ⅱ) 단말기 회로부를 포함한 전체 구조와 SAR를 포함하는 Body effect(+내장형 안테나 성능 열화)를총체적으로 고려해서 설계해야.
Stage 1
Stage 1
Stage 1
Stage 2
Stage 2
Stage 2
Stage 3
Stage 3
Stage 3
Stage 4
Stage 4
Cross bar fractal tree
Koch snowflake
Sierpinski gasket fractal
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■ Concluding remarks
- Let’s review what we have discussed in Chapter. 5
제 5 장. Practical Antennas for Various Applications.
5-1. Small antenna.ⅰ) Electrically small antenna.ⅱ) Physically constrained antenna.ⅲ) Physically small antenna.ⅳ) Planar inverted – F antenna (PIFA).
5-2. Artistic antenna (Fractals).
5-3. 전형적인 handset antenna.
5-4. Active antenna concept- various configuration of active antennas combined with microwave integrated
circuit (MIC).
5-5. Concept of Ultra Wideband (UWB) Antenna.
5-6. Case study – AM 수신용 안테나의 대표적인 예로서의 Ferrite loaded loop (coil) antenna.
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5-7. Case study – GPS (Global Positioning System)용 antenna.
5-8. Multi-band antenna.
5-9. Internal antenna.