This document provides an overview of antennas and wave propagation. It defines an antenna as an electrical conductor that radiates or receives electromagnetic waves. Key antenna parameters discussed include radiation pattern, beam area, directivity, gain, and radiation resistance. Common antenna types like dipoles, loops, and arrays are examined. The document also covers topics such as effective aperture, polarization, and the radiation characteristics of half-wave dipoles and Yagi-Uda antennas.

1. Antenna and Wave
Propagation
S.Mahendrakumar
Asst. Prof. (Sr. Gr.)
Department of ECE
Velalar College of Engineering and
Technology, Erode.

2. Basic Communication System
Transmitter Transmission Medium Receiver
Input
Transducer
Output
Transducer
Noise
wired / wireless

3. 2. Wireless Communication
Tx Rx
Communication media
 Cellular
 WLAN
 Satellite Communication
 Radio, TV Broadcast

4. What is an antenna?
• An antenna is an electrical conductor or system of conductors
• Transmission - radiates electromagnetic energy into space
• Reception - collects electromagnetic energy from space
• Region of transition between guided and free space propagation
• Often part of a signal transmitting system over some distance
• Not limited to electromagnetic waves (e.g. acoustic waves)

5. Basic Antenna Parameters
• Radiation pattern
• Beam area and beam efficiency
• Effective aperture and aperture efficiency
• Directivity and gain
• Radiation resistance

6. Radiation pattern
• Far field patterns
• Field intensity decreases with increasing distance, as 1/r
• Radiated power density decreases as 1/r2
• Pattern (shape) independent on distance
• Usually shown only in principal planes

2
D
2
r
:
field
Far  D : largest dimension of the antenna
e.g. r > 220 km for APEX at 1.3 mm !

7. Radiation pattern (2)
)
,
( 


E )
,
( 


E
2
0
2
2
)
,
(
)
,
(
)
,
( r
Z
E
E
P





 
 

Field patterns
max
)
,
(
)
,
(
)
,
(






P
P
Pn 
+ phase patterns
)
,
( 

 )
,
( 


HPBW: half power beam width

8. 0
30
60
90
120
150
180
210
240
270
300
330
Power pattern of 2 isotropic sources
Pn

d 1

2
  0 deg

0
30
60
90
120
150
180
210
240
270
300
330
Power pattern of 2 isotropic sources
Pn

d 1

2
  90
 deg

0
30
60
90
120
150
180
210
240
270
300
330
1.5
1
0.5
0
Field P attern of 2 isotropic sources
E i
 
i
0
30
60
90
120
150
180
210
240
270
300
330
Power pattern of 2 isotropic sources
Pn

d 1

2
  45
 deg

0
30
60
90
120
150
180
210
240
270
300
330
1.5
1
0.5
0
Field P attern of 2 isotropic sources
E i
 
i
0
30
60
90
120
150
180
210
240
270
300
330
Power pattern of 2 isotropic sources
Pn

d 1

2
  135
 deg

Radiation Pattern

9. Beam Area and Beam Efficiency

  





 







4
2
0 0
)
,
(
)
sin(
)
,
( d
P
d
d
P n
n
A
Main beam area
Minor lobes area


  d
P
beam
Main
n
M )
,
( 



  d
P
lobes
or
n
m
min
)
,
( 

m
M
A 




Beam area
A
M
M




Main beam efficiency

10. Effective Aperture and Aperture Efficiency
Receiving antenna extracts power from incident wave
e
in
rec A
S
P 

For some antennas, there is a clear physical aperture and an aperture efficiency can
be defined
p
e
ap
A
A


A
e
A


2

Aperture and beam area are linked:

11. Directivity and Gain
average
P
P
D
)
,
(
)
,
( m ax





A
n d
P
D










4
)
,
(
4
4
Isotropic antenna: 
4

A 1

D
2
4

 e
A
D 
From pattern
From aperture
only
losses
ohmic
to
due
lower than
is
)
1
(0
factor
efficiency
Gain
D
G
k
k
D
k
G
g
g
g




Directivity

12. Radiation Resistance
• Antenna presents an impedance at its terminals
A
A
A jX
R
Z 

• Resistive part is radiation resistance plus loss resistance
L
R
A R
R
R 

The radiation resistance does not correspond to a real resistor present in the antenna but to the resistance of space
coupled via the beam to the antenna terminals.

13. Radiation Resistance
• Antenna presents an impedance at its terminals
A
A
A jX
R
Z 

• Resistive part is radiation resistance plus loss resistance
L
R
A R
R
R 

The radiation resistance does not correspond to a real resistor present in the antenna
but to the resistance of space coupled via the beam to the antenna terminals.

14. Antenna Equivalent Circuit

15. Short dipole
)
1
1
(
2
)
cos(
3
2
0
)
(
0
r
j
cr
le
I
E
r
t
j
r








)
1
1
(
4
)
sin(
3
2
2
0
)
(
0
r
j
cr
r
c
j
le
I
E
r
t
j






 



)
1
(
4
)
sin(
2
)
(
0
r
cr
j
le
I
H
r
t
j









2
r
1
as
varies
P
r
1
as
vary
H
E
,
2




and
r
for 
•Length much shorter than wavelength
•Current constant along the length
•Near dipole power is mostly reactive
•As r increases Er vanishes, E and H gradually become in phase


 


l
r
e
I
j
E
r
t
j
)
sin(
60 )
(
0



16. RADIATED POWER AND RADIATED RESISTANCE

17. RADIATED POWER AND RADIATED RESISTANCE

18. RADIATED POWER AND RADIATED RESISTANCE

19. RADIATED POWER AND RADIATED RESISTANCE

20. RADIATION FROM HALF-WAVE DIPOLE

21. RADIATION FROM HALF-WAVE DIPOLE
(1)

22. RADIATION FROM HALF-WAVE DIPOLE
(2)

23. RADIATION FROM HALF-WAVE DIPOLE
(3)
(4)

24. RADIATION FROM HALF-WAVE DIPOLE
(5)
(6)

25. RADIATION FROM HALF-WAVE DIPOLE
(7)

26. RADIATION FROM HALF-WAVE DIPOLE

27. RADIATION FROM HALF-WAVE DIPOLE

28. RADIATION FROM HALF-WAVE DIPOLE
(8)

29. RADIATION FROM HALF-WAVE DIPOLE

31. dBi versus dBd
•dBi indicates gain vs. isotropic antenna
•Isotropic antenna radiates equally well in all directions,
spherical pattern
•dBd indicates gain vs. reference half-wavelength dipole
•Dipole has a doughnut shaped pattern with a gain of 2.15 dBi
dB
dBd
dBi 15
.
2



32. Received power
,
,
, 
t
t
et G
P
A
• Receiving antenna
• Transmitting antenna
r
r
er G
P
A ,
,
t
r
t
r
t
t
r P
G
G
r
G
r
P
G
P
2
2
2
4
4
4















S, power density Effective receiving area

33. Classification of Antenna
• Linearly polarised antennas Circularly polarised antennas
• Narrow-band Broad-band
• Wire
• Aperture
• Arrays

34. Polarisation of EM wave
Electrical field, E
vertical
horizontal
circular

35. Types of Antenna
• Wire
• Aperture
• Arrays

36. Wire Antenna
• Dipole
• Loop
• Folded dipoles
• Helical antenna
• Yagi (array of dipoles)
• Corner reflector
• Many more types
Horizontal dipole

37. Aperture antenna
• Collect power over a well defined aperture
• Large compared to wavelength
• Various types:
• Reflector antenna
• Horn antenna
• Lens

38. Antenna Arrays
 Motivations: to achieve desired high gain or radiation pattern, and the
ability to provide an electrically scanned beam.
 It consists of more than one antenna element and these radiating
elements are strategically placed in space to form an array with desired
characteristics which are achieved by varying the feed (amplitude and
phase) and relative position of each radiating element;
 The main drawbacks are the complexity of the feeding network required
and the bandwidth limitation (mainly due to the feeding network)

39. Yagi-Uda Antennas

40.  The driven element (feeder) is the very heart of the antenna. It determines the
polarisation and centre frequency. For a dipole, the recommended length is about 0.47
to ensuring a good input impedance to a 50 Ω feed line.
 The reflector is longer than the feeder to force the radiated energy towards the front. The
optimum spacing between the reflector and the feeder is between 0.15 to 0.25
wavelengths.
 The directors are usually 10 to 20% shorter than the feeder and appear to direct the
radiation towards the front. The director to director spacing is typically 0.25 to 0.35
wavelengths,
 The number of directors determines the maximum achievable directivity and gain.

41. Log-periodic Antennas