1
1
Chapter 2 :
Fundamental parameters of antennas
• From Radiation Pattern
– Radiation intensity
– Beamwidth
– Directivity
– Antenna efficiency
– Gain
– Polarization
• From Circuit viewpoint
– Input Impedance
2
Chapter 2 : Topics
(2)
• Antenna effective length and effective area
• Friis transmission equation
• Radar range equation
3
Definition of Radiation Pattern
• Once the electromagnetic (EM) energy
leaves the antenna, the radiation pattern
tells us how the energy propagates away
from the antenna.
• Definition :
Mathematical function or a graphical
representation of the radiation properties
of an antenna as a function of space
coordinates
4
Radiation Pattern Example
5
Radiation Pattern (1)
• Can be classified as:
– Isotropic, directional and omnidirectional
• Isotropic: Hypothetical antenna having equal
radiation in all directions
• Directional: having the property or receiving
EM energy more effectively in some directions
other than others
• Omnidirectional: having an essentially
nondirectional pattern in a given plane and a
directional pattern in any orthogonal plane
6
Radiation Pattern (2)
• Principal patterns (or planes):
– E-plane : the plane containing the electric field
vector and the direction of maximum radiation
– H-plane : the plane containing the magnetic
field vector and the direction of maximum
radiation
2
7
Radiation Pattern (3)
Omnidirectional
Eθ
Hφ
8
Field Regions
9
Reactive Near Field Region
• Region surrounding the antenna, wherein the
reactive field predominates
]
62
.
0
,
2
max[
2
:
antenna)
(small
For
62
.
0
:
For
3
3
λ
π
λ
π
λ
λ
λ
λ
D
R
R
D
D
R
D
<
⇒
<
<
<
>
Angular field distribution depends on distance from
antenna
10
Radiating Near Field Region
• Region between reactive near-field and far-
field regions (Fresnel zone)
]
62
.
0
,
2
max[
]
2
,
3
max[
2
3
:
antenna)
(small
For
62
.
0
2
:
For
3
2
3
2
λ
π
λ
λ
λ
π
λ
λ
λ
λ
λ
λ
D
R
D
R
D
D
R
D
D
>
>
⇒
>
>
<
>
>
>
Radiation fields predominate but angular field
distribution still depends on distance from antenna
11
Far