15 feb 2001property of r. struzak1 antenna fundamentals (1) prof. r. struzak...

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 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 These materials may not be published, copied to or issued from another Web server without the author's express permission.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

• Introduction

• PFD

• Directivity and Gain

• EIRP


Introduction


Radio Link

Antenna

Transmitter

Antenna

Receiver

Antennas: important elements of any radio link

Radio wave


Photographs of

Various Antenna Types


T-Antenna

• Transmitting antenna transforms power in the form of time-dependent electrical currentinto time-and-space-dependent electro-magnetic (EM) wave.


R-Antenna

• Receiving antenna transforms time-and-space-dependent EM wave into time-dependent electrical current (power)


Intended Antennas

• Radiocommunication antennas– Transmitting

– Receiving

• EM applicators– Industrial

– Medical

• Measuring antennas


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)


PFD


PFD: Isotropic Radiator

Notes• Loss-less propagation medium

assumed

• Isotropic radiator cannot be physically realized

• PFD does not depend on frequency/ wavelength

24 r

PPFD T

r

Power Flux Density (PFD)


PFD: Distance Dependence

0.01

0.1

1

10

100

0.1 1 10

Distance

PFD


PFD: Example 1

• What is the PFD from TV broadcast GEO satellite at Trieste?

• EIRP = 180 kW (52.5 dB(W))

• Distance: ~38'000 km• Free space )dB(Wm 100

Wm101

108.1

108.1

)1038(4

10108.1

2

2-11

16

5

26

32

PFD


PFD: Example 2

• What is the PFD from a hand-held phone at the head?

• EIRP = 180 mW• Distance = ~3.8 cm• Free space

)dB(Wm 10

Wm10

108.1

108.1

)108.3(4

108.1

2-

2-

2

1

22

1

PFD


PFD: Example 3

• What is the ratio of the powers required to produce the same power 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


PFD concept

• Used often in the management/ regulating the use of the radio frequency spectrum

• To define the restrictions imposed on radiocommunication systems

• To assure electromagnetic compatibility • Relates to the field-strength of plane wave


PFD Limits

• The WRC 2000 decided that the PFD at the Earth’s surface produced by emission from a space station in Fixed-satellite service shall not exceed the limit 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

[d

B(W

m^

2)]


PFD: Real Antenna

• PFD produced by physically realizable antennas depends on– power and distance (as isotropic source)– horizontal direction angle ()– vertical direction angle ()


Directivity and Gain


Radiation Intensity

• Radiation intensity = Power per steradian = = (,) [watts/steradian]x

y

z

OP

Transmitting antenna r

Distance (r) is very large

• measure of the ability of an antenna to concentrate radiated power in a particular direction


Antenna Directivity

• D Has no units• Note:

P0 = power radiated

4

),(),(),(

0PD

avg

4

intensityradiation Average

sin),(

radiatedpower Total

0avg

0

2

00

P

ddP


Antenna Gain

• The directivity and gain are measures of the ability of an antenna to concentrate power in a particular direction.

• Directivity – power radiated by antenna (P0 )

• Gain – power delivered to antenna (PT)

: radiation efficiency (50% - 75%)

• G has no units – Usually relates to the peak

directivity of the main radiation lobe

– Often expressed in dB– Known as “Absolute Gain”

or “Isotropic Gain”

0

),(),(

P

P

DG

T


PFD vs. Antenna Gain

S0 = PFD produced by a loss-less isotropic radiator

0

20

2

),(4

),(

),(

))((

),(),(

SGr

PG

rrrS


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]


Antenna Gain

Actual antenna

P = Power Delivered to the antenna

S = Power receivedat a great distance

Measuring equipment

Reference antenna

Po = Power Delivered to the antenna

S = Power receivedat a great distance

Measuring equipment

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


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)


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 patternin vertical plane

Radiation patternIn horizontal plane


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) in the orthogonal plan

Radiation patternin vertical plane

Radiation patternIn horizontal plane


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


Typical Gain and Beam-widthType 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


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.


EIRP


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


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 RR impose PFD limits of (-160) dB (W/(m2*4kHz)) at the earth surface in Equator (distance 35900 km) ?


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

15 feb 2001property of r. struzak1 antenna fundamentals (1) prof. r. struzak...

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