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Lecture 1Some Introductory Concepts

EE533-08

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Isotropic Radiator• Power is radiated equally in all

directions• F= flux density in Watts/m2

• Also use Field strength, Fs= Volts/m

Pt

224 mWatts

RPF t

π=

2

3

Isotropic Radiator• Power is radiated equally in all

directions• F= flux density in Watts/m2

• Also use Field strength, Fs= Volts/m

Pt

224 mWatts

RPF t

π=

4

Flux Density and Field Strength

224 mWatts

RPF t

π=

Ω==== 377120πεμ

εμ

o

ooZ

meterVolts

RP

RPZF tt

osF 2230

4120

==•=ππ

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Real Antenna – Not IsotropicPolar Plot of Normalized F

0dB

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4

7

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5

9

10

6

11

12

7

13

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Satellite RelayThe “Bent Pipe”

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A full Link Budget will also include a noise analysis

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Factors affecting Free Space Loss

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Factors affecting Free Space Loss

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Factors affecting Free Space Loss

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Plane Earth Loss- LOS

• When the wave interacts with the ground or some other obstruction we no longer have free space propagation to the receiver

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Plane Earth Loss-LOS

• When the wave interacts with the ground or some other obstruction we no longer have free space propagation to the receiver

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Plane Earth Loss- Fresnel Diffraction

• Non-LOS communication involves an additional loss due to Diffraction

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Earth Bulgehttp://www.cisco.com/univercd/cc/td/doc/product/wireless/bbfw/ptop/p2pspg02/spg02ch2.htm#xtocid19

Earth BulgeWhen planning for paths longer than seven miles, the curvature of the earth might become a factor in path planning and require that the antenna be located higher off the ground. The additional antenna height needed can be calculated using the following formula:

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2DH =where H = Height of earth bulge (in feet)D = Distance between antennas (in miles)

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Earth Bulge with Fresnel Diffractionhttp://www.cisco.com/univercd/cc/td/doc/product/wireless/bbfw/ptop/p2pspg02/spg02ch2.htm#xtocid19

Minimum Antenna HeightThe minimum antenna height at each end of the link for paths longer than seven miles (for smooth terrain without obstructions) is the height of the First Fresnel Zone plus the additional height required to clear the earth bulge. The formula would be:

843.43

2DFDH +=

whereH = Height of the antenna (in feet)D = Distance between antennas (in miles)F = Frequency in GHz

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Tower Height

140148125 feet32 Miles115123100 feet28 Miles9510380 feet26 Miles859370 feet24 Miles758360 feet22 Miles657350 feet20 Miles556340 feet18 Miles455330 feet16 Miles404825 feet14 Miles354320 feet12 Miles303815 feet10 Miles253310 feet8 Miles

5.8 GHz 802.11a(Fresnel Zone

Radius = 25 Feet)

2.4GHz 802.11b/g(Fresnel Zone

Radius = 39 Feet)

Tower Height Required Over Tallest Obstacle In Line-of-Sight to Provide

60% Fresnel Zone Clearance

Height of Tower to Avoid Flat

Earth Curvature

Line of Sight Distance

Between Antenna Towers

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Free Space vs Ground effects

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Plane Earth Loss

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Plane Earth Loss

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Plane Earth Loss

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Plane Earth Loss

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Plane Earth Loss

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Plane Earth Loss

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Empirical Path Loss

21 )1()( n

b

n

ddddg −− +=

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Mobile Signal