course antenna engineering wir aopert micro strip 01

1Course Antenna Engineering

Dirk Heberling

3. Antenna Concepts and Analysis

• Wire Antennas• Aperture Antennas• Microstrip Antennas

Dirk Heberling

3.1 Wire Antennas

• Dipole Antennas and Derivates• Antenna Matching and Balancing• Loop Antennas• Yagi-Uda Antennas• Helix Antennas and Broadband

Antennas• Mobile Phone Antennas

Dirk Heberling

Wire antennas 1

• Oldest antenna form• Most prevalent antenna form• Nearly any imaginable antenna shape

and configuration• Simple concept• Easy construction• Inexpensive

Dirk Heberling

Wire antennas 2• Many analytical solutions have been

presented• Modern numerical solutions

- Simple concepts, e.g. Method of Moments (MoM)

- Easy application to computers- Usable for many wire configurations

• High accuracy of simple theory

Dirk Heberling

Example of a wire antennas

Base station antenna for GSM

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Straight Wire Dipole 1

current distribution

( ) sin , z2 2mL LI z I k z⎛ ⎞⎛ ⎞= − ≤⎜ ⎟⎜ ⎟⎝ ⎠⎝ ⎠

for L < λ /2

Maximum current at the terminals:

( )0 sin2mLI z I k⎛ ⎞= = ⎜ ⎟

⎝ ⎠Source: W.L. Stutzman, G.A. Thiele: Antenna Theory and Design, Wiley, New York, 1981

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Straight Wire Dipole 2

current distribution for various centre-fed dipoles

Source: W.L. Stutzman, G.A. Thiele: Antenna Theory and Design, Wiley, New York, 1981

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Straight Wire Dipolefarfield pattern 1

The radiation integral: ( ) ( ) ' cos2

jkzLf I z e dzθθ −

−= ∫

leads to the far-zone electric field:

cos cos cos2 2

kL kLeE j I

−⎛ ⎞ ⎛ ⎞−⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

for L = λ/2:

( )cos cos

π θθ

⎛ ⎞⎜ ⎟⎝ ⎠=

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for L = λ:

( ) ( )cos cos 12sin

Fπ θ

for L = 3λ/2:

3cos cos20.7148

π θθ

⎛ ⎞⎜ ⎟⎝ ⎠=

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Radiation pattern for L = 1.25λSource: C. A. Balanis, Antenna Theory, 2nd Ed. Wiley, New York, 1997

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Straight Wire DipoleInput impedance 1

with the radiated power Pr:

2 22 2

cos cos cos1 2 2 sin

2 sin2m

kL kLIP r d d

π π θη θ θ φ

η θπ

⎧ ⎫⎛ ⎞ ⎛ ⎞−⎜ ⎟ ⎜ ⎟⎪ ⎪⎪ ⎪⎝ ⎠ ⎝ ⎠= ⎨ ⎬⎪ ⎪⎪ ⎪⎩ ⎭

∫ ∫

the radiation resistance Rr gives:

= for L = λ/2: 73rR = Ω

Dirk Heberling

for L = λ/2: 73 42.5inZ j= + Ω

Dirk Heberling Source: C. A. Balanis, Antenna Theory, 2nd Ed. Wiley, New York, 1997

Input resistance Rin (Ω)Length L

20π2(L/λ)20<L<λ/4

24.7(π L/λ)2.4λ/4<L< λ/220π2(L/λ)20<L<λ/4

11.14(π L/λ)4.17λ/2<L< 0.637λ24.7(π L/λ)2.4λ/4<L< λ/2

20π2(L/λ)20<L<λ/4

Approximations for the input impedance:

Dirk HeberlingSource: W.L. Stutzman, G.A. Thiele: Antenna Theory and Design, Wiley, New York, 1981

0.49λ

Resonant length L ShorteningL/2a

2%50000.475λ0.49λ

5%502%5000

Straight Wire Dipole, shortening by thick wires

0.455λ0.475λ0.49λ

9%105%502%5000

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Folded Dipole Antenna 1

Transmission line mode

Antenna mode

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4in DZ Z=

for L = λ/2

Folded Dipole Antenna 2

212F in FP Z I=

Dipole

212D in DP Z I=

in the antenna mode12F DI I=

Folded dipole

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Antenna Matching and Feeding

Two primary feeding considerations:

• Matching between transmission line and antenna

• Excitation of the current distribution on the antenna

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Antenna Matching 1

Important point:• Good matching not

always necessary• High voltages can arise

on the feeding line with high power applications

Ways of matching:• Discrete matching

network• λ/4-line transformer• Tuning devices like

stubs etc.

Reflected and transmitted power in relation to VSWR

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Antenna Matching 2

sin2in m inLI I zβ⎡ ⎤⎛ ⎞= −⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

Change of input impedance:

in rmin

Off-centre feeding of a full wave dipole

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Antenna Matching 3

( )21in aZ Zα+

' / 4l λfor

α current division factorbetween the wires

4in aZ Z

for equal radii conductors

The T-Match

Source: C. A. Balanis, Antenna Theory, 2nd Ed. Wiley, New York, 1997

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Antenna Balancing 1

unbalanced currents I1 > I2

Example:Cross section of a coaxial transmission line feeding a

dipole at its centre

balanced currents I1 = I2

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BALanced to UNbalancedThe Balun

Coax-fed dipole

Sleeve balun-fed

dipole

Equivalent circuit

Cross section of a sleeve balun

Split coax balun

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Wire antennas above imperfect ground

Elevation pattern of a vertical short dipole at the surface of the ground plane

( )cos cossin4

jkrjkh jkh

VIL eE j e e

rθ θ

θ ωμ θπ

−−= + Γ

with 2

cos sincos sin

ε θ ε θ

′ ′− −Γ =

′ ′+ −

and ro

j σε εωε

′ = −

typical: 15rε =

213 210 3 10m

σ − −Ω

= − ⋅Source: W.L. Stutzman, G.A. Thiele: Antenna Theory and Design, Wiley, New York, 1981

Dirk Heberling

Loop AntennasThe radiation resistance

of a small loop is

2 31,1713r

kS SR πηλ λ

⎛ ⎞⎛ ⎞ ⎛ ⎞= ⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠ ⎝ ⎠

Increase of the loop resistance by:

Several turns of number n2

231,171rSR n

λ⎛ ⎞⎜ ⎟⎝ ⎠

Introduction of a ferrite core of effective permeability μeff

231,171r effSR nμ

λ⎛ ⎞⎜ ⎟⎝ ⎠

Typical μeff: 100 - 10,000

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Square Loop Antennas 1

For the one-wavelength square loop antenna:

( )0ˆ cos x8

I kx λ′ ′= = − ≤1 2I I x

( )0ˆ sin y8

I ky λ′ ′= − = ≤4 3I I y

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yz-plane

xz-plane

Principle plane patterns for one-wavelength square loop antenna

xy-plane

Source: W.L. Stutzman, G.A. Thiele: Antenna Theory and

Design, Wiley, New York, 1981

Square Loop Antennas 2

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Square Loop Antenna, Input Impedance

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Circular Loop, Equivalent Circuit

( ) ( )in in in r L A iZ R jX R R j X X= + = + + +

Rr = radiation resistanceRL = loss resistance of loop conductor

XA = external inductive reactance = ω LA

Xi = internal high-frequency reactance = ω Li

Dirk Heberling

Yagi-Uda Antenna 1

A parasitic linear array of parallel dipoles is called aYagi-Uda antenna

Yagi-Uda arrayor

First published by Shintaro Uda 1926

Simplification of an antenna array if only a few elements are fed directly.

Up to now,all arrays examined have had all elements active, requiring a direct

connection to each element.

Such an array is referred to as a parasitic array.

Dirk Heberling

Example of a Yagi-Antenna

Yagi-Antenna for TV and Radio reception

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Yagi-Uda Antenna 2

Field incident to a parasitic element is:

incident driverE E=

0 incident parasiteE E= +withtangential to the parasite

Consider a driver element that is a half-wave dipole and a parasitic element very close to it

parasite incident driverE E E= − = −then

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Yagi-Uda Antenna 3

Driver of length 0.4781λ

Parasite of length 0.49λ

Driver of length 0.4781λ

Parasite of length 0.45λ

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Yagi-Uda Antenna 4

Three-element Yagi-Uda antenna

- Driver of length 0.4781λ- Reflector of length 0.49λ- Director of length 0.45λ

H-plane

E-plane

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Yagi-Uda Antenna 5

Configuration of a general Yagi-Uda antenna

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Yagi-Uda Antenna 6Radiation pattern of a six-element Yagi-Uda antenna for TV Channel 15

H-plane E-plane

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Broadband Antennas 1An antenna with wide bandwidth is referred to as a

Broadband antennaThe term „broadband“ is a relative measure of the

bandwidth and varies with the circumstances

With fU and fL the upper and lower frequency of operation and fC the centre frequency

Bandwidth as a percent of the centre frequency 100U L

f ff−

× Bandwidth defined as a ratio

If the impedance and the pattern of an antenna do not change significantly over about an octave (fU/fL=2) or more, we classify it as a

broadband antenna

Dirk Heberling

Broadband Antennas 2

• Broadband antennas– Helical antennas– Biconical antennas– Discone monopole

• Frequency independent antennas– Spiral antennas– Log-periodic antennas

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Helical Antennas

D = diameter of the helixC = circumference of the helix Dπ=S = spacing between turns

α = pitch angle 1tanS

L = total length NS=

L0 = length of one turn 2 2S C= +

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Helical Antennas, Normal Mode

Radiation patternEquivalent model

for 0NL λFarfield consists of dipole field ED and loop field EL

Circular polarization for 2C Sλ=

Helical antenna

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Helical Antennas, Axial Mode

with: 3 44 3

< <- Circumference in

the range of

4S λ- Spacing about

12 14α° ≤ ≤ °- Pitch angle usually

Typical farfield pattern

Left-hand sensed helix

Right-hand sensed helix

Axial (endfire) mode of helix

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Log-Periodic Dipole Array (LPDA)

Construction details of the LPDA

A log-periodic antenna is an antenna having a structural geometry such that its impedance and radiation characteristics repeat periodically as the

logarithm of frequency

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Log-Periodic Dipole Array 2A wedge of enclosed angle α bounds the dipole lengths!

L L LLR R R R

= = = =with

1 1 1n n

R LR L

τ + += = <the scale factor τ is given by:

σ =and the spacing factor σ is defined as:

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Example of a

Dirk Heberling

Example of a LPDAFarfield Pattern

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Helical Antenna

Loop Antenna

Inverted-F Antenna

Sleeve-Dipole

Basic antenna types

Antennas for Mobiles 1

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Influence of the human body on the electromagnetic field

Antennas for Mobiles 2

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Example of a printed loop antenna

Realisation forms of loop antennas

Antennas for Mobilesthe loop-antenna

Equivalent circuit and matching circuit

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Principle of a sleeve dipole Current distributionon a cellular phone

Antennas for Mobilesthe sleeve-dipole

Dirk Heberling

Model of a helical antenna Operational modes

Antennas for Mobilesthe helical antenna

Dirk Heberling

Examples of Inverted-F Antennas

λ/4-Monopol

InvertedL-Antenne

InvertedF-Antenne (IFA)

PlanareInvertedF-Anenne(PIFA)

λ/4-Monopole

InvertedL-Antenna

InvertedF-Antenna (IFA)

Planar InvertedF-Antenna (PIFA)

Antennas for Mobilesthe inverted-F antenna

Dirk Heberling

Shortening and loading of antennas

Antennas for MobilesMiniaturization

a) Introduction of an inductance b) Surrounding by dielectric or magnetic materialsc) Introduction of a capacitance

Dirk Heberling

CONCEPT-Model of a cellular phone with an

helical antenna

CONCEPT-Modelof a cellular phone at

the user

Antennas for Mobiles, an Example 1

Calculated radiation patterns at 450 MHz

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CONCEPT-Modelof the mobile phone

Calculated magnetic nearfield at450 MHz (cut plane through the device)

Simulated nearfield behaviour

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η = P rad (with user)

P rad (without user)

Overall efficiency

EID-Antenna: • Concentration of the nearfield in the feeding point• Electrical decoupled from the casing

lelektr =λ0/2

Principle of the EID-Antenna

Optimised nearfield distribution

Optimised overall efficiency

Optimised Antenna: EID-Antenna

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Mobile phone with EID-antenna

Cellular phone withhelical antenna

Calculated magnetic nearfield atf = 450 MHz (cut plane through the device)

CONCEPT: Nearfield Characteristics

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η = 38 % η = 84 %

Mobile phone with EID-antenna

with user

CONCEPT: Farfield @ 450 MHz

Mobile phone with helical antenna

with user

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φ=270°

φ=180°

φ=90°

φ=0°

Measurement Situation

Measurement: Farfield @ 450 MHz

Handy, freistehendHandy mit EID am BenutzerHandy mit Helix am Benutzer

φ in °

Measured horizontal farfield characteristic

Mobile Phone, without userMobile Phone, with EID and userMobile Phone, with helix and user

Dirk Heberling

Integrated Antennas

Dualband- and Multiband-Antennas

Antenna Interaction

Antennas for MobilesDevelopment Trends

Dirk Heberling

1. Metallic patch 2. 3D-MID-Antennas 3. Ceramic Antennas

• very popular• good electrical properties• easy fabrication• mech. fixation necessary

• difficult fabrication • flexible antenna design• electric properties depend

on the material

• antenna design difficult• small size• difficult fabrication

Antennas for MobilesIntegrated Antenna Technology

Dirk Heberling

0,8 1 1,2 1,4 1,6 1,8 2-20

free spacetalking position

Return Loss (S11)

Antennas for MobilesDualband Helical Antenna

Double Helical Antenna

Dirk Heberling

Antennas for MobilesInteraction with the Head

course antenna engineering wir aopert micro strip 01

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