Transmission Lines - FEUP

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Faculdade de Engenharia

Transmission Lines

ELECTROMAGNETIC ENGINEERINGMAP – TELE 2008/2009

EE 0809Lines 2

Faculdade de EngenhariaTransmission Lines

transmission lines à waveguides supporting TEM waves

parallel-plate waveguides

coaxial waveguides

two-wire waveguides

most common types

EE 0809Lines 3

Faculdade de EngenhariaTransmission Lines

general transmission line equations

time-harmonic solutions

finite transmission lines

voltage, current and impedance along the line

transmission lines in circuits

Smith chart

impedance matching

λ/4 transformer

reactive elements

single-stub

double-stub

transients

today

next week

EE 0809Lines 4

Faculdade de EngenhariaTEM waves in parallel-plate waveguides

b

y

z

x

W

xE

H

yEE

ˆ

ˆ

00

00

η−=

=r

r

βγ j= xeE

H

yeEE

zj

zj

ˆ

ˆ

0

0

β

β

η−

−=

=r

r

inside the guide:

EE 0809Lines 5

Faculdade de EngenhariaVoltage between the plates

b

y

z

x

W

voltage between the plates: zjebE β−−= 0

∫ ⋅−=−2

1

12

P

P

ldEVVrr

xeE

H

yeEE

zj

zj

ˆ

ˆ

0

0

β

β

η−

−=

=r

rinside the guide:

zjy eEE β−= 0

( ) ∫−=b

ydyEzV0

voltage à

EE 0809Lines 6

Faculdade de EngenhariaCurrent density on the plates

b

y

z

x

W

xeE

H

yeEE

zj

zj

ˆ

ˆ

0

0

β

β

η−

−=

=r

r

1

2

na

current density on the plates:

upper plate:

yan ˆˆ −=

inside the guide:

lower plate:

yan ˆˆ = 1

2

na

( )21ˆ HHaJ ns

rrr−×=

02 =Hr

xeEH zj ˆ01

β

η−−=

r( ) zeEbyJ zj

s ˆ0 β

η−−==

r

02 =Hr

xeEH zj ˆ01

β

η−−=

r ( ) zeEyJ zjs ˆ0 0 β

η−==

r

EE 0809Lines 7

Faculdade de EngenhariaCurrent on the plates

b

y

z

x

W

upper plate current:

∫ ⋅=A

sdJIrr

zjeEW β

η−−= 0

xeE

H

yeEE

zj

zj

ˆ

ˆ

0

0

β

β

η−

−=

=r

rinside the guide:

( ) zeEbyJ zjs ˆ0 β

η−−==

r

currentà

( ) ∫ ⋅=W

s zdxJzI ˆr

( ) zeE

byJ zjs ˆ0 β

η−−==

r

( ) zeE

yJ zjs ˆ0 0 β

η−==

r

current density:

lower plate current: zjeEW β

η−+= 0( ) ∫ ⋅=

Ws zdxJzI ˆ

r

EE 0809Lines 8

Faculdade de EngenhariaLossless transmission line equations

b

y

z

x

W

( ) zjebEzV β−−= 0

( ) zjeEWzI β

η−−= 0 zj

zj

eE

WjdzdI

ebEjdzdV

β

β

ηβ

β

=

=

0

0

εµη

εµωβ

=

=

VbW

jdzdI

IW

bj

dzdV

εω

µω

−=

−= ( )H/mW

bL

µ=

( )C/mbW

= VCjdzdI

ILjdzdV

ω

ω

−=

−=

0

0

22

2

22

2

=+

=+

LCIdz

Id

LCVdz

Vd

ω

ω

eqs. for V e I in a losslesstransmission line

EE 0809Lines 9

Faculdade de EngenhariaEquivalent circuit of a lossless transmission line

differential length ∆z of a transmission line:

zL∆

zC∆

z∆

i(z+∆z,t)i(z,t)

+ +

--v(z,t) v(z+∆z,t)

( )t

tzizLvL ∂

∂∆=

,

( )t

tzzvzCiC ∂

∆+∂∆=

,

( ) ( ) ( )

( ) ( ) ( ) 0,,

,

,,

,

=∆++∂

∆+∂∆+−

∆++∂

∂∆=

tzzit

tzzvzCtzi

tzzvt

tzizLtzv

EE 0809Lines 10

Faculdade de EngenhariaEquivalent circuit of a lossless transmission line

zL∆

zC∆

z∆

i(z,t)

+

-v(z,t)

( ) ( ) ( )

( ) ( ) ( ) 0,,

,

,,

,

=∆++∂

∆+∂∆+−

∆++∂

∂∆=

tzzit

tzzvzCtzi

tzzvt

tzizLtzv

( ) ( )

( ) ( )t

tzvCz

tzit

tziLz

tzv

∂∂=

∂∂−

∂∂=

∂∂−

,,

,, ( ) ( )

( ) ( )zVCjdz

zdI

zILjdz

zdV

ω

ω

=−

=−

0lim →∆z

phasor notation0

0

22

2

22

2

=+

=+

LCIdz

Id

LCVdz

Vd

ω

ω

same as before

EE 0809Lines 11

Faculdade de EngenhariaEquivalent circuit of a lossy transmission line

differential length ∆z of a transmission line:

zR∆ zL∆

zG∆zC∆

z∆

i(z+∆z,t)i(z,t)

+ +

--v(z,t) v(z+∆z,t)

( )( )

ttzi

zLv

tzizRv

L

R

∂∂

∆=

∆=,

,

( )( )

ttzzv

zCi

tzzvzGi

C

G

∂∆+∂

∆=

∆+∆=,

,

( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) 0,,

,,

,,

,,

=∆++∂

∆+∂∆+∆+∆+−

∆++∂

∂∆+∆=

tzzit

tzzvzCtzzvzGtzi

tzzvt

tzizLtzizRtzv( ) ( ) ( )

( ) ( ) ( )t

tzvCtzvG

ztzi

ttzi

LtziRz

tzv

∂∂

+=∂

∂−

∂∂

+=∂

∂−

,,

,

,,

,0lim →∆z

EE 0809Lines 12

Faculdade de EngenhariaGeneral transmission line equations

( ) ( ) ( )

( ) ( ) ( )t

tzvCtzvG

ztzi

ttzi

LtziRz

tzv

∂∂

+=∂

∂−

∂∂

+=∂

∂−

,,

,

,,

,

( ) ( ) ( )

( ) ( ) ( )zVCjGdz

zdI

zILjRdz

zdV

ω

ω

+=−

+=−

general solution

i(z,t)

+

-v(z,t)

( )( )CjGLjR ωωγ ++=

( ) ( )

( ) ( )zIdz

zId

zVdz

zVd

22

2

22

2

γ

γ

=

=

βαγ j+= ( )( ) zz

zz

eIeIzI

eVeVzVγγ

γγ

−−+

−−+

+=

+=

00

00

propagation constant

attenuation constant

phase constant

phasor notation

EE 0809Lines 13

Faculdade de Engenharia

( ) zz eVeVzV γγ −−+ += 00

Attenuation and phase constants

±gV

−0V

+0V

gZ

z

+

−( )zV

( )zI

( ) ( ) tjzz eeVeVtzv ωγγ −−+ += 00Re,

( ) ( ) ztjzztjz eeVeeV βωαβωα +−−−+ += 00Re

−+00 and VVif are real

( ) ( )zteVzteV zz βωβω αα ++−= −−+ coscos 00

z

atenuation phase

EE 0809Lines 14

Faculdade de Engenharia

( ) zz eVeVzV γγ −−+ += 00

Voltage and current in transmission line

( ) ( ) ( )

( ) ( ) ( )zVCjGdz

zdI

zILjRdz

zdV

ω

ω

+=−

+=−

( ) zz eIeIzI γγ −−+ += 00

γωLjR

IV +

=+

+

0

0 only 2 constantsare required

4 constants required to define voltage and current

−=0

0

IV

++

+= 00 V

LjRI

ωγ

−−

+−= 00 V

LjRI

ωγ

±gV

−−00 , IV

++00 , IV

gZ

z

+

−( )zV

( )zI

EE 0809Lines 15

Faculdade de EngenhariaCharacteristic impedance

Characteristic impedanceà

( )Ω++

=CjGLjR

ωω

infinite lineà no reflections

ratio between voltage and current for an infinite length transmission line

( ) zeIzI γ−+= 0

( ) zeVzV γ−+= 0

γωLjR +

=

characteristic impedance

( )( )CjGLjR ωωγ ++=

±gV

−−00 , IV

++00 , IV

gZ

z

+

−( )zV

( )zI

+

+

=0

0

IV

( )zZ

( ) ( )( )zIzV

zZ = ( ) 0ZzZ =

note: in general 00

0

0

0 ZIV

IV

=−= −

+

+

EE 0809Lines 16

Faculdade de EngenhariaSummary

Propagation constantà ( )( ) ( )1m−++=+= CjGLjRj ωωβαγ

( )Ω++

=CjGLjR

Zωω

0

Propagation velocityà

Characteristic impedanceà

( )1ms −=βω

v

Wavelengthà ( )m2βπ

λ =

General case

•frequency dependent attenuation

•frequency dependent velocity

SIGNAL DISTORTION

EE 0809Lines 17

Faculdade de EngenhariaTransmission lines – special cases

LCjωγ =

CL

Z =0 LCv

1=

Lossless lines

NO DISTORTION

0== GR ( )( )CjGLjRj ωωβαγ ++=+=

CjGLjR

Zωω

++

=0 βω

=v

LCωβ

α

=

= 0

Distortionless linesCG

LR

=

( )LC

LjR ωγ +=

CL

Z =0LC

v1

=LC

LC

R

ωβ

α

=

=

•zero or constant attenuation•constant velocity•constant and real characteristic impedance

EE 0809Lines 18

Faculdade de EngenhariaTransmission-line parameters

In turn, these parameters depend on the line geometry and on the materials thatconstitute the line

Letσ à dielectric conductivityσC à conductor conductiviityε à electric permitivitty of the dielectricµ à magnetic permeability of the dielectricµC à magnetic permeability of the conductor

The behaviour of a transmission line depends on the operating frequency andon parameters R, L, G and C

EE 0809Lines 19

Faculdade de EngenhariaTransmission-line parameters

a

b

a

D

a

hW

2h

coaxial two-wire conductor over ground parallelplate

EE 0809Lines 20

Faculdade de EngenhariaFinite transmission lines

LLL IZV =

( ) ( ) ( )[ ]( ) ( ) ( )[ ]z

Lz

LL

zL

zLL

eZZeZZIZ

zI

eZZeZZIzV

γγ

γγ

000

00

21

21

−−+=

−++=

( )

( ) zozo

zo

zo

eZV

eZV

zI

eVeVzV

γγ

γγ

00

−−

+

−−+

−=

+=

±gV

gZ

0

+

−( )zV

( )zI

( )zZ

LZ+

−( )zV

( )zI

+

−LV

LI

zl−0

0

0

0

0 ZIV

IV

=−=−

+

+

( )( ) zz

zz

eIeIzI

eVeVzVγγ

γγ

−−+

−−+

+=

+=

00

00

00

0

0

ZV

ZV

I

VVV

oL

oL

−+

−+

−=

+= ( )

( )00

00

2121

ZZIV

ZZIV

LL

LL

−=

+=

+

0=z

EE 0809Lines 21

Faculdade de EngenhariaImpedance along the transmission line

z

LZ±gV

gZ

+

−( )zV

( )zI

( )zZ

+

−( )zV

( )zI

+

−LV

LI

( ) ( )( )

( ) ( )( ) ( ) z

Lz

L

zL

zL

eZZeZZeZZeZZ

ZzIzV

zZ γγ

γγ

00

000

−−+−++

== −

( ) ( ) ( )[ ]( ) ( ) ( )[ ]z

Lz

LL

zL

zLL

eZZeZZIZ

zI

eZZeZZIzV

γγ

γγ

000

00

21

21

−−+=

−++=

( ) ( ) ( )( ) ( ) L

zzzz

zzL

zz

ZeeZeeZeeZee

ZzZ γγγγ

γγγγ

−−+−−+

= −−

−−

0

00

( ) ( )( )zZZ

zZZZzZ

L

L

γγ

tanhtanh

0

00 −

−=

'z

( ) ( )( )'tanh

'tanh'

0

00 zZZ

zZZZzZ

L

L

γγ

++

=

xx

xx

eeee

x −

+−

=)tanh(

EE 0809Lines 22

Faculdade de EngenhariaInput impedance – lossless transmission line

z

LZ±gV

gZ

+

−( )zV

( )zI

( )zZ

+

−( )zV

( )zI

+

−LV

LI

'z

lossless line βγ j=( ) ( )xjjx tantanh =

( ) ( )( )'tan

'tan'

0

00 zjZZ

zjZZZzZ

L

L

ββ

++

=

length l

( )( )ljZZ

ljZZZZ

L

Lin β

βtantan

0

00 +

+=

( ) ( )( )'tanh

'tanh'

0

00 zZZ

zZZZzZ

L

L

γγ

++

=

EE 0809Lines 23

Faculdade de EngenhariaInput impedance of lossless transmission lines – special cases

lossless transmission line of length l ( )( )ljZZ

ljZZZZ

L

Lin β

βtantan

0

00 +

+=

0ZZ L = 0ZZ in =

∞=LZ ( )ljZZ in βcotg0−=

nl = Lin ZZ =

0=LZ ( )lanjZZ in βt0=

( )4

12λ

−= nlL

in ZZ

Z20=

always imaginary

EE 0809Lines 24

Faculdade de EngenhariaReflection coefficient at the load

Reflection coefficient (voltage)à ratio between reflected and incident voltages

( )( ) +

==

==Γ

00

0

VV

zV

zV o

inc

refL

at the load:

0

0

ZZZZ

L

LL +

−=Γ

( )

( )00

00

2121

ZZIV

ZZIV

LL

LL

−=

+=

+

Special cases:

0ZZ L = 0=ΓL

∞=LZ 1=ΓL

0=LZ 1−=ΓL

no reflections MATCHED LINE

EE 0809Lines 25

Faculdade de EngenhariaReflection coefficient at the load

0

0

ZZZZ

L

LL +

−=Γ

Notes:

1. For current

2. Most often, is complex àLΓ ΓΓ=Γ θjLL e||

Linc

refI

VV

II

I

IΓ−=−===Γ +

+

0

0

0

0

1

1

0

0

+

−=Γ

ZZZZ

L

L

L 11

+−

=ΓL

LL z

z

LL z

ZZ

=0

( )( ) LL

LL

jxrjxr

+++−

=11

LL jxr +=

1||, ≤ΓL

EE 0809Lines 26

Faculdade de EngenhariaReflection coefficient along the line

( )( ) +

==

==Γ

00

0

VV

zV

zV o

inc

refLat the load: ΓΓ=

+−

=Γ θjL

L

LL e

ZZZZ

0

0

along the line:( )( )

zLz

zo

inc

ref eeVeV

zV

zVz γ

γ

γ2

0

)( Γ===Γ −+

zz −='

'2)'( zLez γ−Γ=Γ

lossless line: βγ j= ( )'2)'( zjL ez βθ −ΓΓ=Γ absolute value is constant

EE 0809Lines 27

Faculdade de EngenhariaVoltage along the line

( ) zjzj eVeVzV ββ −−+ += 00

z

( ) ( ) ( )zjzjzj eeVeVVzV βββ −−−−+ ++−= 000

( ) ( ) ( )zVeVVzV zj ββ cos2 000−−−+ +−=

( )2

cosjxjx ee

x−+

=

propagating wave

stationary wave

EE 0809Lines 28

Faculdade de EngenhariaNote – propagating and stationary waves

•let ( ) zjAezV β−=•let ( ) ( ) ( )ztAAeeAetzv ztjtjzj βωβωωβ −=== −− cosReRe,

zpropagating wave

( ) ( )zAzV βcos=•let ( ) ( ) ( ) ( )tzAezAtzv tj ωββ ω coscoscosRe, ==

stationary wavez

nodes( v=0 for every t )

EE 0809Lines 29

Faculdade de EngenhariaVoltage along the line

( ) zjzj eVeVzV ββ −−+ += 00

z

propagating + stationary waves

( ) ( )zjL

zj eeVzV ββ 20 1 Γ+= −+

( ) ( )( ) ( )( )( )'2cos21

'2sin'2cos1'

20

220

zV

zzVzV

LL

LL

βθ

βθβθ

−Γ+Γ+=

−Γ+−Γ+=

Γ+

ΓΓ+

periodic termperiod=λ/2

( ) ( )( )( )'2'

0

'2'0

1

1'zj

Lzj

zjL

zj

eeV

eeVzVβθβ

ββ

−+

−+

ΓΓ+=

Γ+=

'z

EE 0809Lines 30

Faculdade de EngenhariaVoltage along the line - example

( ) ( )'2cos21'2

0 zVzV LL βθ −Γ+Γ+= Γ+

Let

( )m2m1

5.0

V1

1

4

0

πλβ

π

=⇒=

=

+

j

L e

V

0123456789100

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

minV

MAXV

EE 0809Lines 31

Faculdade de EngenhariaVoltage maxima and minima

•voltage minima: ( ) 1'2cos −=−Γ zβθ

( ) ( )'2cos21'2

0 zVzV LL βθ −Γ+Γ+= Γ+

•location: πβθ nzM 22 / −=−Γ ( )Γ+= θπβ

nzM 221/

n

z 0'≥

integer

•location: ( )πβθ 122 / +−=−Γ nzm ( )[ ]Γ++= θπβ

1221/ nzm

n

z 0'≥

integer

•value: LLVV Γ−Γ+= + 212

0min( )LVV Γ−= + 10min

•value: LLMAXVV Γ+Γ+= + 21

20 ( )LMAX

VV Γ+= + 10

•voltage maxima: ( ) 1'2cos +=−Γ zβθ

EE 0809Lines 32

Faculdade de EngenhariaVoltage along the line - example

( ) ( )'2cos21'2

0 zVzV LL βθ −Γ+Γ+= Γ+

Let

( )m2m1

5.0

V1

1

4

0

πλβ

π

=⇒=

=

+

j

L e

V

0123456789100

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

minV

MAXV

( ) 5.110 =Γ+= +LMAX

VV

( ) 5.010min=Γ−= +

LVV

85π

πλ

=28

/ ππ += nzM

85/ π

π += nzm

EE 0809Lines 33

Faculdade de EngenhariaSWR

SWR (Voltage Standing Wave Ratio)à ratio between voltage maxima and minima

( )( )L

LMAX

V

V

V

VSWR

Γ−

Γ+==

+

+

1

1

0

0

min L

LSWRΓ−

Γ+=

1

1

11

+−

=ΓSWRSWR

L

Note: 1≥SWR

EE 0809Lines 34

Faculdade de EngenhariaSWR – particular cases

0

0

ZZZZ

L

LL +

−=Γ

L

LSWRΓ−

Γ+=

1

111

+−

=ΓSWRSWR

L

Particular cases:

0ZZ L = 0=ΓL minVV MAX =

no reflections

no stationary wave

1=SWR 0=ΓL

matched line 1=SWR

1=SWR

EE 0809Lines 35

Faculdade de EngenhariaSWR – particular cases

0

0

ZZZZ

L

LL +

−=Γ

L

LSWRΓ−

Γ+=

1

111

+−

=ΓSWRSWR

L

Particular cases:

∞=LZ 1=ΓL

0=LZ 1−=ΓL ∞=SWR

( ) ++ =Γ+= 00 21 VVV LMAX

( ) 010min=Γ−= +

LVV

∞=SWR

+= 02VVMAX

0min

=V

EE 0809Lines 36

Faculdade de EngenhariaCurrent along the line

( ) zjzj eIeIzI ββ −−+ += 00

z

propagating + stationary waves

( ) ( )zjL

zj eeZV

zI ββ 2

0

0 1 Γ−= −+

( ) ( )( ) ( )( )

( )'2cos21

'2sin'2cos1'

2

0

0

22

0

0

zZ

V

zzZ

VzI

LL

LL

βθ

βθβθ

−Γ−Γ+=

−Γ−+−Γ−=

Γ

+

ΓΓ

+

periodic termperiod=λ/2

( ) ( )

( )( )'2'

0

0

'2'

0

0

1

1'

zjL

zj

zjL

zj

eeZV

eeZV

zI

βθβ

ββ

−+

−+

ΓΓ−=

Γ−=

'z

EE 0809Lines 37

Faculdade de EngenhariaCurrent maxima and minima

•current minima: ( ) 1'2cos =−Γ zβθ

( ) ( )'2cos21' 2

0

0z

Z

VzI LL βθ −Γ−Γ+= Γ

+

•location: ( )πβθ 12'2 +−=−Γ nz ( )[ ]Γ++= θπβ

1221

' nzn

z 0'≥

integer

•location: πβθ nz 2'2 −=−Γ ( )Γ+= θπβ

nz 221

'n

z 0'≥

integer

•value: LLZ

VI Γ−Γ+=

+

21 2

0

0

min( )LZ

VI Γ−=

+

10

0

min

•value: LLMAX Z

VI Γ+Γ+=

+

21 2

0

0 ( )LMAX Z

VI Γ+=

+

10

0

•current maxima: ( ) 1'2cos −=−Γ zβθ

EE 0809Lines 38

Faculdade de EngenhariaVoltage and current – maxima and minima location

( ) 1'2cos =−Γ zβθ

( ) ( )'2cos21' 2

0

0z

Z

VzI LL βθ −Γ−Γ+= Γ

+

( )[ ]Γ++= θπβ

1221/ nzm

n

z 0'≥

integer

( )Γ+= θπβ

nzM 221/

n

z 0'≥

integer

( ) 1'2cos −=−Γ zβθ

( ) ( )'2cos21' 20 zVzV LL βθ −Γ+Γ+= Γ+

máximos de tensãoe

mínimos de corrente

voltage maximaAND

current minima

voltage minimaAND

current maxima

EE 0809Lines 39

Faculdade de EngenhariaTransmission lines in circuits

±gV

gZ

0

LZ+

−inV

inI

+

−LV

LI

( )( )lzII

lzVV

VZIV

in

in

inging

−==−==

+=

( )

( ) zozo

zo

zo

eZV

eZV

zI

eVeVzV

γγ

γγ

00

−−

+

−−+

−=

+=

zl−+− Γ= 00 VV L

[ ][ ]l

Ll

in

lL

lin

eeZV

I

eeVV

γγ

γγ

2

0

0

20

1

1

−+

−+

Γ−=

Γ+=

( ) ( )[ ]lL

lLg

lg eZeZe

ZV

V γγγ 20

2

0

0 11 −−+

Γ++Γ−=

EE 0809Lines 40

Faculdade de EngenhariaTransmission lines in circuits

±gV

gZ

0

LZ+

−inV

inI

+

−LV

LI

zl−

( ) ( )[ ]lL

lLg

lg eZeZe

ZV

V γγγ 20

2

0

0 11 −−+

Γ++Γ−=

( )[ ]lLgg

gl

eZZZZ

VZeV

γ

γ

200

00 −

+

Γ−++=

0

0

ZZZZ

g

gg +

−=Γ (reflection coefficient at the source)

[ ]lLg

g

g

l

e

V

ZZZ

eVγ

γ

20

00

1 −

+

ΓΓ−+=

( )

( )

ΓΓ−Γ−

+=

ΓΓ−Γ+

+=

−−

−−

lLg

zLz

g

lg

lLg

zLz

g

lg

ee

eZZ

eVzI

ee

eZZ

eVZzV

γ

γγ

γ

γ

γγ

γ

2

2

0

2

2

0

0

11

11

voltage and current as functions of

LZload:

line:

source:

lZ ,,0 γ

gg ZV ,

EE 0809Lines 41

Faculdade de EngenhariaTransmission lines in circuits

±gV

gZ

0

LZ+

−inV

inI

+

−LV

LI

zl−

( )

( )

ΓΓ−Γ−

+=

ΓΓ−Γ+

+=

−−

−−

lLg

zLz

g

lg

lLg

zLz

g

lg

ee

eZZ

eVzI

ee

eZZ

eVZzV

γ

γγ

γ

γ

γγ

γ

2

2

0

2

2

0

0

11

11

( ) ( )( ) 122

0

0 11−−−

ΓΓ−Γ++

= lLg

zL

z

g

lg eee

ZZ

eVZzV γγγ

γ

( ) ( ) ( ) ( )

+ΓΓΓ+ΓΓ+ΓΓΓ+ΓΓ+Γ+

+= −−−−−−−

LzL

lLg

zlLg

zL

lLg

zlLg

zL

z

g

lg eeeeeeeeee

ZZ

eVZ γγγγγγγγγγγ

222222

0

0

( ) ( )

+ΓΓ+ΓΓ+Γ+

+= −−−

L222

0

0 1 lLg

lLg

zL

z

g

lg eeee

ZZ

eVZ γγγγγ

L++++=−

3211

1xxx

x

EE 0809Lines 42

Faculdade de EngenhariaTransmission lines in circuits

±gV

gZ

0

LZ+

−inV

inI

+

−LV

LI

zl−

( ) ( ) ( ) ( ) ( )

+ΓΓΓ+ΓΓ+ΓΓΓ+ΓΓ+Γ+

+= −−−−−−−

LzL

lLg

zlLg

zL

lLg

zlLg

zL

z

g

lg eeeeeeeeee

ZZ

eVZzV γγγγγγγγγγ

γ222222

0

0

( ) L++++++= −−+−−+−−+ zzzzzz eVeVeVeVeVeVzV γγγγγγ332211

−−+ Γ= 12

2 VeV lg

γ

+− Γ= 33 VV L

−−+ Γ= 22

3 VeV lg

γ

+2V

+− Γ= 22 VV L

−2V

g

lg

ZZ

eVZV

+=

−+

0

01

γ

+1V

+− Γ= 11 VV L

−1V

EE 0809Lines 43

Faculdade de EngenhariaTransmission lines in circuits

±gV

gZ

0

LZ+

−inV

inI

+

−LV

LI

zl−

( ) L++++++= −−+−−+−−+ zzzzzz eVeVeVeVeVeVzV γγγγγγ332211

+2V

−2V

+1V

−1V

( ) ( ) ( ) zzzz eVeVeVVVeVVVzV γγγγ −−+−−−−+++ +=+++++++= 00321321 LL

EE 0809Lines 44

Faculdade de EngenhariaPower in lossless transmission lines

( ) ( )( )( ) ( )( )'2'

0

0

'2'0

1'

1'

zjL

zj

zjL

zj

eeZV

zI

eeVzV

βθβ

βθβ

−+

−+

Γ

Γ

Γ−=

Γ+=

(lossless transmission line)

( ) ( ) ( ) ''Re21

' * zIzVzPav =

( ) ( )( ) ( ) ( )( )

Γ−Γ+= −−−+

−+ ΓΓ '2'

0

*0'2'

0 11Re21

' zjL

zjzjL

zjav ee

ZV

eeVzP βθββθβ

( ) ( )( ) '2'22

0

2

01Re

2zjzj

LL eeZ

Vβθβθ −−−

+

ΓΓ −Γ+Γ−=

( ) '2sin21Re2

2

0

2

0zj

Z

VLL βθ −Γ+Γ−= Γ

+

( ) ( ) constant12

' 2

0

2

0=Γ−=

+

Lav Z

VzP

incident reflected

EE 0809Lines 45

Faculdade de EngenhariaPower in transmission lines – general case

( ) ( )( )( ) ( )( )'2'2''

0

0

'2'2''0

1'

1'

zjzL

zjz

zjzL

zjz

eeeeZV

zI

eeeeVzV

βθαβα

βθαβα

−−+

−−+

Γ

Γ

Γ−=

Γ+=( ) ( ) ( ) ''Re

21

' * zIzVzPav =

( ) ( )( ) ( ) ( )( )

Γ−Γ+= −−−−+

−−+ ΓΓ '2'2''

0

*0'2'2''

0 11Re21

' zjzL

zjzzjzL

zjzav eeee

ZV

eeeeVzP βθαβαβθαβα

( ) '2sin21Re2

'2'42'2

0

2

0zejee

R

Vz

Lz

Lz βθααα −Γ+Γ−= Γ

−−+

( ) ( )'22'2

0

2

0

2' z

Lz

av eeR

VzP αα −

+

Γ−= ( ) ( )2

0

2

0, 1

20' LavLav R

VzPP Γ−===

+

( ) ( )lL

lavinav ee

R

VlzPP αα 222

0

2

0, 2

' −+

Γ−===

00 RZ =if

EE 0809Lines 46

Faculdade de EngenhariaProblem

formulae

EE 0809Lines 47

Faculdade de EngenhariaProblem

formulae

EE 0809Lines 48

Faculdade de EngenhariaProblem

formulae

EE 0809Lines 49

Faculdade de EngenhariaProblem

formulae

EE 0809Lines 50

Faculdade de Engenharia

( )

( ) 22

22

22

1

21

1

imre

imL

imre

imreL

x

r

Γ+Γ−

Γ=

Γ+Γ−

Γ−Γ−=

Load impedance ó reflection coefficient

11

+−

=ΓL

LL z

zwhere

0ZZ

z LL = (normalized load impedance)

00 RZjXRZ LLL

=+=

(lossless line)

LLL jxrz +=

imrej

LL je Γ+Γ=Γ=Γ Γθ

L

LLz

Γ−Γ+

=11

( )( ) imre

imreLL j

jjxr

Γ−Γ−Γ+Γ+

=+11

EE 0809Lines 51

Faculdade de Engenharia

reΓ

imΓ

( )

( ) 22

22

22

1

21

1

imre

imL

imre

imreL

x

r

Γ+Γ−

Γ=

Γ+Γ−

Γ−Γ−=

Load impedance ó refelction coefficient

22

2

11

1

+

=Γ+

+

−ΓL

imL

Lre rr

r

Lr+11

L

L

rr+1

( ) ( ) 220

20 Ryyxx =−+−

( )0

1=Γ

+=Γ

im

LLre rrcentered at

circle of radius ( )Lr+11

the reflection coefficients of all ZLwhose real part is rL are in this circle

EE 0809Lines 52

Faculdade de Engenharia

reΓ

imΓ

Load impedance ó reflection coefficient

22

2

11

1

+

=Γ+

+

−ΓL

imL

Lre rr

r

Note:

curve does not depend on xL

0=Γim 111

,, =Γ∨+−

=Γ rreL

Llre r

r

111

+−

L

L

rr

0=Lr 1, −=Γ lre

for any ZL

∞=Lr 1, =Γ lre

1−

open circuit

EE 0809Lines 53

Faculdade de Engenharia

reΓ

imΓ

( )

( ) 22

22

22

1

21

1

imre

imL

imre

imreL

x

r

Γ+Γ−

Γ=

Γ+Γ−

Γ−Γ−=

Load impedance ó reflection coefficient

( )2

2 111

=

−Γ+−Γ

LLimre xx

( ) ( ) 220

20 Ryyxx =−+−

circle of radius Lx1

Lim

re

x11

=Γ=Γcentered at

Lx1

Lx1

1

1≤ΓL

the reflection coefficients of all ZLwhose imaginary part is xL are here

EE 0809Lines 54

Faculdade de Engenharia

reΓ

imΓ

Load impedance ó reflection coefficient

Lx1

Lx1

1

Note:

curve does not depend on rL

( )2

2 111

=

−Γ+−Γ

LLimre xx

Lx1

0=Lx

0=Lx infinite radius

symmetrical curves for xL < 0

EE 0809Lines 55

Faculdade de EngenhariaSmith chart

reΓ

imΓ

1

xL constant

rL constant

EE 0809Lines 56

Faculdade de EngenhariaSmith chart

EE 0809Lines 57

Faculdade de Engenharia

Γθ

reΓ

imΓ

Smith chart

1

LZ

•from:

point in chart ( intersection of curves corresponding to rL and xL )

ΓθandLΓ

rL and xL

Lx

Lr

•from:

EE 0809Lines 58

Faculdade de EngenhariaReflection coefficient along the line

along the line:

zz −='

'2)'( zLez γ−Γ=Γ

lossless line: βγ j= ( )'2)'( zjL ez βθ −ΓΓ=Γ

reΓ

imΓ

1

constant magnitude

phase decreases with z’

toward generator

toward load

( )( ) 0

0)(ZzZZzZ

z+−

Note:

( )( )

zLz

zo

inc

ref eeVeV

zV

zVz γ

γ

γ2

0

)( Γ===Γ −+

Smith chart can be used to obtain from ( )zZ )(zΓ

EE 0809Lines 59

Faculdade de EngenhariaDistances in the Smith chart

in Smith chart the distances are measured as fractions of λ

reΓ

imΓ

1

toward generator

toward load

( )'2)'( zjL ez βθ −ΓΓ=Γ when πβ 2'2 =z

222

βπ

==z

a complete turn (360º)

corresponds to a distance = λ/2

initial position

EE 0809Lines 60

Faculdade de EngenhariaInput impedance

1. draw the point corresponding to the normalized load impedance zL à point P1

2. draw the circle centered at the origin with radius OP1

3. draw the straight line from O to P1

4. draw the straight line from O that corresponds to a rotation of l toward the generator

5. intersection of this line with previous circle à point P2

6. obtain , where zin is read from P2

reΓ

imΓ

1

0ZzZ inin ⋅=

P1

P2

EE 0809Lines 61

Faculdade de EngenhariaAdmittance

reΓ

imΓ

1

( ) ( )( )'tan

'tan'

0

00 zjZZ

zjZZZzZ

L

L

ββ

++

= ( )( ) LL

L

ZZ

jZZjZZ

ZzZ20

0

00 2tan

2tan4

' =++

=

=

ππλ

( )LZ

ZZ

Z 0

0

4=

λ( ) Lyz =4λ

º3602 ⇔λ

º1804 ⇔λ

1. draw zL

2. rotate 180º

Ly

Lz

EE 0809Lines 62

Faculdade de EngenhariaMaxima and minima location

( ) ( )'2cos21'2

0

0z

Z

VzI LL βθ −Γ−Γ+= Γ

+

( ) ( )'2cos21' 20 zVzV LL βθ −Γ+Γ+= Γ+

( ) 1'2cos =−Γ zβθ à voltage maxima and current minima

à voltage minima and current maxima( ) 1'2cos −=−Γ zβθ

( ) ( )'2' zjL ez βθ −ΓΓ=Γ

voltage maxima where ( ) πnz 2' =Γ∠

voltage minima where ( ) ( )π12' +=Γ∠ nz

EE 0809Lines 63

Faculdade de EngenhariaMaxima and minima location

reΓ

imΓ

1

voltage maxima where ( ) πnz 2' =Γ∠

voltage minima where ( ) ( )π12' +=Γ∠ nz

voltage maxima

voltage minima

Note:

1. maxima and minima where input

impedance is real

2. maxima (minima) points are separated

by nλ/2

EE 0809Lines 64

Faculdade de EngenhariaProblem

EE 0809Lines 65

Faculdade de EngenhariaProblem

EE 0809Lines 66

Faculdade de EngenhariaProblem

EE 0809Lines 67

Faculdade de EngenhariaProblem