Antenna Basics 1

8/4/2019 Antenna Basics 1

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15 Feb 2001 Property of R. Struzak 1

Antenna Fundamentals (1)

Prof. R. [email protected]

School on Digital and Multimedia Communications Using Terrestrial and Satellite Radio Links

The Abdus Salam International Centre for Theoretical Physics ICTP Trieste (Italy) 12 February2 March 2001


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Note: These materials may be used for study,research, and education in not-for-profitapplications. If you link to or cite these materials,please credit the author, Ryszard Struzak. Thesematerials may not be published, copied to orissued from another Web server without theauthor's express permission. Copyright 2001

Ryszard Struzak. All commercial rights arereserved. If you have comments or suggestions,please contact the author [email protected].


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Summary Slide

Introduction

PFD

Directivity and Gain

EIRP


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Introduction


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Radio Link

Antenna

Transmitter

Antenna

Receiver

Antennas: important elements of any radio link

Radio wave


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Photographs

ofVarious Antenna Types


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T-Antenna

Transmitting antenna transforms

power in the form of time-dependent electrical current

intotime-and-space-dependent electro-magnetic (EM)

wave.


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R-Antenna

Receiving antenna transformstime-and-space-dependent EM wave

intotime-dependent electrical current (power)


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Intended Antennas

Radiocommunication antennas

Transmitting

Receiving EM applicators

Industrial

Medical

Measuring antennas


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Unintended Antennas

Any conductor/ installation carrying electrical

current

(e.g. electrical installation of vehicles) Any conducting structure/ installation irradiated by

EM waves

Permanent (e.g. Antenna masts, or power network)

Time-varying (e.g. Windmills, or helicopter propellers)

Transient (e.g. Re-radiating aeroplane)


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PFD


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PFD: Isotropic Radiator

Notes

Loss-less propagation medium

assumed Isotropic radiator cannot be

physically realized

PFD does not depend on

frequency/ wavelength

24 r

P

PFDT

r

Power Flux Density (PFD)


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PFD: Distance Dependence

0.01

0.1

1

10

100

0.1 1 10

Distance

PFD


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PFD: Example 1

What is the PFD fromTV broadcast GEOsatellite at Trieste?

EIRP = 180 kW(52.5 dB(W))

Distance: ~38'000 km Free space

)dB(Wm100

Wm101

108.1

108.1

)1038(4

10108.1

2

2-11

16

5

26

32

PFD


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PFD: Example 2

What is the PFDfrom a hand-held

phone at the head?

EIRP = 180 mW

Distance = ~3.8 cm

Free space)dB(Wm10

Wm10

108.1

108.1

)108.3(4

108.1

2-

2-

2

1

22

1

PFD


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PFD: Example 3

What is the ratio of the

powers required to

produce the samepower flux density at a

GEO- satellite and at a

LEO-satellite.?

Distances: GEO: 38 000 km

LEO: 1 000 km

14441000

380002

2

LEO

GEO

GEO

LEO

LEO

GEO

LEO

GEO

P

P

Dist

Dist

P

P

PFD

PFD


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PFD concept

Used often in the management/ regulating the use

of the radio frequency spectrum

To define the restrictions imposed onradiocommunication systems

To assure electromagnetic compatibility

Relates to the field-strength of plane wave


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PFD Limits

The WRC 2000 decided that the

PFD at the Earths surface

produced by emission from a

space station in Fixed-satellite

service shall not exceed thelimit shown in the figure.

The figure is valid for stations

at the geostationary orbit in

frequency band 10.7-11.7 GHz

and reference band 4 kHz. For

other cases see RR Table S21-4. -152

-150

-148

-146

-144

-142

-140

-138

0 10 20 30 40 50 60 70 80 90

Angle of arrival (above the horizontal plane)

PFD[dB(Wm^2)]


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PFD: Real Antenna

PFD produced by physically realizable

antennas depends on

power and distance (as isotropic source)

horizontal direction angle ()

vertical direction angle ()


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Directivity and Gain


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Radiation Intensity

Radiation intensity =Power

per steradian ==(,) [watts/steradian]

x

y

z

OPTransmitting

antennar

Distance (r) is very large

measure of the ability

of an antenna to

concentrate radiated

power in a particular

direction


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Antenna Directivity

D Has no units

Note:

P0 = power radiated

4

),(),(),(

0P

Davg

4

intensityradiationAverage

sin),(

radiatedpowerTotal

0avg

0

2

00

P

ddP


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Antenna Gain

The directivity and gain

are measures of the ability

of an antenna toconcentrate power in a

particular direction.

Directivitypower

radiated by antenna (P0 ) Gainpower delivered to

antenna (PT)

: radiation efficiency(50% - 75%)

G has no units

Usually relates to the peakdirectivity of the mainradiation lobe

Often expressed in dB

Known as AbsoluteGain or Isotropic Gain

0

),(),(

P

P

DG

T


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PFD vs. Antenna Gain

S0 = PFD produced by a loss-less isotropic radiator

0

2

0

2

),(

4),(

),(

))((

),(),(

SG

r

PG

rrrS


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Other Definitions of Gain

For practical purposes, the antenna gain is defined as the

ratio (usually in dB), of the power required at the input of a

loss-free reference antenna to the power supplied to the

input of the given antenna to produce, in a given direction,the same field strength or the same power flux-density at

the same distance.

When not specified otherwise, the gain refers to the

direction of maximum radiation. The gain may be considered for a specified polarization.

[RR 154]


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Antenna Gain

Actual

antenna

P = Power

Delivered to

the antenna

S = Power

received

at a great

distance

Measuring

equipment

Reference

antenna

Po = Power

Delivered to

the antenna

S = Power

received

at a great

distance

Measuring

equipment

Antenna Gain (in the specific direction) = P / Po


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Reference Antennas

Isotropic radiator

isolated in space (Gi, absolute gain, or isotropic gain)

Half-wave dipole isolated in space, whose equatorial plane of symmetry

contains the given direction (Gd)

Short vertical antenna

(much shorter than /4), close to, and normal to a

perfectly conducting plane which contains the given

direction (Gv)


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Reference Antennas (1)

Isotropic antenna

Sends (receives) energy

equally in (from) all

directions

Gain = 1 (= 0 dB)

When supplied by P,

produces at distance r power

flux density = P /(4r2)

Theoretical concept, cannot

be physically realized

Radiation pattern

in vertical plane

Radiation pattern

In horizontal plane


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Reference Antennas (2)

Half-Wave Dipole

Linear antenna, realizable

Gain = 1.64 (= 2,15 dB) in

the direction of maximum

radiation

Figure-eight-shaped radiation

pattern in the dipole plane,

omnidirectional (circular) inthe orthogonal plan

Radiation pattern

in vertical plane

Radiation pattern

In horizontal plane


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Typical radiation pattern

Omnidirectional

Broadcasting

Mobile telephony Pencil-beam

Microwave links

Fan-beam (narrow in one plane, wide in the other)

Shaped-beam

Satellite antennas


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Typical Gain and Beam-width

Type of antenna Gi[dB] HPBW [0]

Isotropic 0 360x360

Dipole 2 360x120

Helix (10 turn) 14 35x35

Small dish 16 30x30

Large dish 45 1x1


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Gain and Beam-width

Gain and beam-width of directive antennas are

inter-related

G ~ 30000 / (1*2)

1 and 2 are the 3-dB beam-widths (in degrees)in the two orthogonal principal planes of antenna

radiation pattern.


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EIRP


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e.i.r.p.

Equivalent Isotropically Radiated

Power (in a given direction):

The product of the power supplied to the

antenna and the antenna gain relative to

an isotropic antenna in a given direction


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e.i.r.p.: Example 1

PFD = e.i.r.p./(4d2)

e.i.r.p. = PFD*(4d2)

-160 dB 10-16 W/(m2*4kHz)

d2 ~ 1.29*1015m2

4d2 ~ 4*1015m2

e.i.r.p. ~ 0.4 W/4kHz

What is the maximum

e.i.r.p. of a GEO

satellite station if RRimpose PFD limits of

(-160) dB

(W/(m2*4kHz)) at the

earth surface inEquator (distance

35900 km) ?


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15 Feb 2001 Property of R Struzak 36

e.r.p.

Effective Radiated Power (in a given

direction):

The product of the power supplied to the

antenna and its gain relative to a half-wave

dipole in a given direction

Antenna Basics 1

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