15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (2) R. Struzak [email protected] School on Digital and Multimedia Communications Using

15 Feb 2001 Property of R. Struzak 1

Antenna Fundamentals (2)

R. [email protected]

School on Digital and Multimedia Communications Using Terrestrial and Satellite Radio LinksThe Abdus Salam International Centre for Theoretical Physics ICTP Trieste (Italy) 12 February – 2 March 2001


• Note: These materials may be used for study, research, and education in not-for-profit applications. If you link to or cite these materials, please credit the author, Ryszard Struzak. These materials may not be published, copied to or issued from another Web server without the author's express permission. Copyright © 2001 Ryszard Struzak. All commercial rights are reserved. If you have comments or suggestions, please contact the author at [email protected].


Summary Slide

• Power Transfer

• EM Field

• Linear Antenna

• Radiation Resistance

• Radiation Pattern


Power Transfer


Antenna Effective Area

• Measure of the effective absorption area presented by an antenna to an incident plane wave.

• Depends on the antenna gain and wavelength

][m ),(4

22

GAe

Aperture efficiency: a = Ae / AA: physical area of antenna’s aperture, square meters


Power Transfer in Free Space

: wavelength [m]

• PR: power available at the receiving antenna

• PT: power delivered to the transmitting antenna

• GR: gain of the transmitting antenna in the direction of the receiving antenna

• GT: gain of the receiving antenna in the direction of the transmitting antenna

• Matched polarizations

2

2

2

4

44

rGGP

G

r

PG

APFDP

RTT

RTT

eR


Power Transfer: Example 1

• What is the power received from GEO satellite (=0.1m, PT =440 W, GT=1000) at Trieste (distance ~38'000 km, GR=1)?

• Free spacedB(W) 150

W101

104.4

10104.4

10384

1.010104.4

4

15

18

25

2

632

2

r

GGPP RTTR


Power Transfer: Example 2

• What is the power from a transmitter (=0.1m, PT=440 mW, GT=1) received at distance of 3.8 cm (GR=1)?

• Free space )dB(W 50

W10

104.4

104.4

108.34

1.011104.4

4

5

8

3

2

21

2

r

GGPP RTTR


EM Field


EM Field of Linear Current Element

x

y

z

OP

r

ErE

E

HHHH

EEEE

r

r

dz: electric current element (short electrical dipole)

dz222

222

HHHH

EEEE

r

r


EM Field of Current Element

2

0

)(sin120

)(cos2

)(sin

HHE

eQFFjA

H

eCQAE

eCjQFFjAE

r

rj

rjr

rj

3

2

2

)(

1

)(

1

1

30

rC

rQ

rFF

IdzA

Johnson & Jasik: Antenna Engineering Handbook; T. Dvorak: Basics of Radiation Measurements, EMC Zurich 1991; J. Dunlop, D. Smith Telecommunications Engineering1995, p. 216

Idz: “moment of linear current element”


Field Components

0.001

0.01

0.1

1

10

100

1000

0.1 1 10

Relative distance

Rel

ativ

e fi

eld

stre

ng

th

FF

FF

Q

Q

C

C


Field ImpedanceField impedance

Z = E/H depends

on the antenna type and on distance

0.01

0.1

1

10

100

0.01 0.1 1 10 100

Distance / (lambda/ 2Pi)

Z /

377

Short dipole

Small loop


Far-Field, Near-Field • Near-field region:

– Angular distribution of energy depends on distance from the antenna;

– Reactive field components dominate (L, C)

• Far-field region: – Angular distribution of energy is independent on

distance;

– Radiating field component dominates (R)


EM Field: Elementary Current Loop

2

0

)(sin

)(cos2

)(sin120

EEH

eQFFBE

eCQBH

eCjQFFBH

r

rj

rjr

rj

LoopAreaIdm

dmB

4

3

dm: “magnetic dipole moment”


Linear Antenna


Arbitrary Linear Antenna

• I(z): antenna current • r: distance

2

2

)()(sin60

l

l

zrjdzezIr

jE


EM Field of Linear Antennas

• Summation of vector components E (or H) produced by every antenna element

• In the far-field region, the vector componentsare parallel to each other

...

...

321

321

HHHH

EEEE

O


Very Short Antenna

• r: distance• Le: effective length of antenna

2

20

)(0

2

2

)(

)(1

sin60

)(sin60

l

l

e

zrje

l

l

zrj

dzzII

L

eLIr

jE

dzezIr

jE


Radiation Resistance


Self- Impedance

• Transmitting antenna • Receiving antenna

jX: energy stored in near-field components (E C, H L)

Rrad: energy radiated

Rlos: energy loss

ZZ

E

E = Electromotive force (open-circuit voltage) induced by radio wave


Short Antenna Radiation Resistance • The PFD in the far

field is given by the Poynting’s vector = |= E|2/(120)

• Antenna radiation resistance = = 802(Le/)2

– For other antennas it is much easier to measure the antenna impedance. 2

0

22

0

320

22

2

2

0

80

sin60

sin2

120

sin60

IL

P

dIL

P

drdS

dSE

P

r

LIE

e

e

S

e


Integration Surface

dS = 2r2sin()d

r

rd

d

rsin


Radiation Pattern


Radiation Pattern

• Radiation Intensity = Power per steradian radiated in a given direction

• Radiation Pattern = Radiation Intensity as function of the azimuth/ elevation angles

• Generally 3 dimensional


Short Dipole in Free Space FF

0

1

0 90 180 270 360

Degrees

Re

lati

ve G

ain

H

V

Horizontal plane: GVi /GVimax = 1

Vertical plane: GHi /GHimax = |sin |

-11


Elements of Radiation Pattern

0-180 180

Emax

Emax /2

Beamwidth

Sidelobes

Nulls

Main lobe • Gain

• Beam width

• Nulls (positions)

• Side-lobe levels (envelope)

• Front-to-back ratio


Long Antenna with Sinusoidal Current Distribution

r: distance

sin2

coscos2

cos60

cossin60

cos)(

cos)(

0

2

2

cos0

0

ll

r

eIjE

dzzeeIr

jE

zrzr

zIzI

rj

l

l

zjrjz

z cos

r(z)

r


Demonstration (Simulation)

LinAntLongThis program simulates radiation pattern of

linear antenna of arbitrary length. It produces 2D radiation diagrams that

show how the positions and magnitudes of radiation lobes, and positions of zeros

depend on the antenna length

C:\My Documents\Ryszard\Articles&Presentations\2001\ICPT2001\Antenna basics\SimulationsXLS\LinAntLong.xls


Half-wave Dipole (l = /2)

• Radiation resistance = 73.1 ohm

sin

cos2

cos60 0

r

eIjE

rj


Half-wave Dipole at Harmonics

0

0.5

1

1.5

-180 -90 0 90 180

Elevation angle, degrees

Re

lati

ve F

ield

-str

en

gth

3rd harmonic

Fundamental

).1,...(1,0);12/(2cos

cos)2/)(12(max)(

.,...1,0);12/()12(cos

)2/)(12(

cos)2/)(12(0)(sin

cos)2/)(12(cos)(

)12()2/(

sin

coscoscos)(

nknk

knf

nknk

k

nf

nf

nL

LL

f

Odd harmonics


Antenna Mask (Example 1)• Typical

relative directivity- mask of receiving antenna (Yagi ant., TV dcm waves)

[CCIR doc. 11/645, 17-Oct 1989)

-20

-15

-10

-5

0

-18

0

-12

0

-60 0

60

12

0

18

0

Azimith angle, degrees

Iso

tro

pic

gai

n, d

B


Antenna Mask (Example 2)

-50

-40

-30

-20

-10

0

0.1 1 10 100

Phi/Phi0

Re

lati

ve g

ain

(d

B)

RR/1998 APS30 Fig.9

COPOLAR

CROSSPOLAR

Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)

0dB

-3dB

Phi0/2

Phi