no slide title · radiowave propagation - [email protected] 27 •e and h fields are...

Radiowave Propagation - Master in Electrical and Computer Engineering

RADIOPROPAGAÇÃO Carlos A. Fernandes

INTRODUCTION

RADIOWAVE PROPAGATION - MEEC [email protected] 2

1. Just go wireless !


2. Who started it?

Maxwell Hertz (1831-1879) (1857-1894)

Marconi

(1874-1937)


2. Who started it?

1895 – Guglielmo Marconi radio station


1887 - Heinrich Herz (experimental verification of Maxwell’s eqs. )

Landmarks

1895 - Marconi, Bose, Popov (developed communication applications)

1901 – First transatlantic radio transmission;

1903 – Start of commercial radio-telegraphy;

1923 – First radio broadcast of audio signals;

1930 – Discovery of cosmic radiation;

1945 – Arthur C. Clark proposes the use of satellites for comm

1913 – Invention of the triode;

1945 – Invention of the transistor

1873 - James Maxwell

3. Some landmarks


Radio wave propagation mechanism is influenced by scenario characteristics

4. Radio propagation scenarios

Compromise between model complexity and accuracy


10 MHz 100 MHz 1 GHz 10 GHz 100 GHz

f

(3 m) (30 m) (30 cm) (3 cm) (3 mm) (l)

Short wave

Broadcast

TV GSM Gbit wireless

LANs

Mobile Comm

3rd generation

Satellite

s

Tendency to shift to higher frequencies:

• Antenna dimension must be at least of the order of l/2 to be

efficient;

• Congestion of the low frequency part of the spectrum

5. Radio services and spectrum


Transceiver Antenna

Guided wave Radiated wave

Transmission line

• Antennas are transducers between guided and radiated waves

• Provide directivity (which may increase with antenna size)

• Antennas are efficient only if its dimensions are comparable or > l/2

(implies the use of high frequency)

6. Transmission and reception systems


e (z, t) = e0 cos(wt - kz)

w = 2 p f

k = w/cm

z [m]

v(z,t)

7. Free space propagation 7.1 Waves

cm = c/n


x [m]

z [m]

e (r, t) = e0 cos(wt - kxx - kzz)

w= 2 p f

k = w/c

k2=kx2+kz

2

f=100 MHz

7. Free space propagation 7.1 Waves (plane wave)


e (r, t) = e0 cos(wt - kr)/ r

w= 2 p f

k = w/c

f =100 MHz

z [m]

r

7.1 Waves (cylindrical wave)

7. Free space propagation

x [m]


e (r, t) = e0 cos(wt - kr)/r

w= 2 p f

k = w/c

f=100 MHz

z [m]

x [m]

r

7. Free space propagation 7.1 Waves (spherical wave)

r


In free space, electric and magnetic fields are mutually orthogonal and orthogonal to the

propagation direction

Vertical polarization

Horizontal polarization

H = k × E / Z0

(Z0 =120p)

k

7. Free space propagation 7.2 Polarization


e (0, t) = e0 cos(wt)

e (0, t) = e0 cos(wt+j)

e(t) = e (t) i + e (t) i

w= 2 p f

k = w/c

f=100 MHz

x

y

x

y

x x y y

7. Free space propagation 7.2 Polarization


8.1 Most common

8. Antennas


SETI

Po-SAT

8.2 Exotic

8. Antennas

GPS


SETI

MBS

Hog-horn antenna for plasma diagnostic in fusion reactor

8.2 Exotic

8. Antennas


MBS

Lens antennas for space applications ESA/ESTEC ILASH Project - 2004

8.2 Exotic

8. Antennas

Lens antennas for mobile applications MBS Project - 1994


Radiation pattern: graphical representation spatial

power density distribution

Rx antenna

Antenna under test

Main lobe

Secondary lobes

8. Antennas 8.3 Main concepts (radiation pattern)


P

8. Antennas 8.3 Main concepts (Directivity and Gain)

P

|E1| |E2|

2

2

2

1

ED

E

=

Same transmit power P

Same distance d

d d

𝐺 = 𝜂𝐷


( )

2

2

1( ) ( )

4r e e rP P G e G r

d

l

p

( ) ( ) ( )21.984 20logre rdB dB dB

e dB

PG G

P d

l

60 e eP GE

d

L

2

1

240

e eP GH

d p

9. Link between antennas in free space


Exercise T1.1

How does free space attenuation compares with coaxial cable attenuation for very long range communications?

Take the following parameter values:

Transmitted power: 1 W

Ge = Gr = 15 dBi

Frequency: 450 MHz

Distance: 50 km

Coaxial cable attenuation: 1.5 dB/100m


t

d

d = c t /2

T

t

t

Tx

Rx

10. Monostatic radar


t

T

t

t

Tx

Rx

( ) ( , )rP i i i S

10. Monostatic radar

11. Before radar (curiosity)


• E and H fields are mutually orthogonal and orthogonal to the propagation direction;

• E and H fields decay with d-1;

• Received power between two antennas decays with d-2; maximum link distance depends on signal/noise ratio at the receiver;

• Received power in a radar decays with d-4; maximum range depends on signal/noise ratio;

• The above distance dependence may change if free-space conditions fail.

12. Summary for free space propagation

no slide title · radiowave propagation - [email protected] 27 •e and h fields are...

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