Download Fundamental of antenna - Telecommunication system

Welcome
Name: Mashhour jumah
ID:202322165
What is an antenna?
• An antenna is an electrical conductor or system of
conductors used for transmission and reception of
electromagnetic waves
• Transmission
• radiates electromagnetic energy into space
• Reception
• collects electromagnetic energy from space
Antenna Fundamentals
Radiation Patterns
3
Antenna Fundamentals
•
Relationship between antenna gain and effective area
4Ae 4f Ae
• G = antenna gain
G 2 
• Ae = effective area

c2
• f = carrier frequency
• c = speed of light (» 3 ´ 108 m/s)
•  = carrier wavelength
2
Property of R Struzak
4
Types of antenna
•
•
Antenna types: actually there are many types of Antenna and
there some of them:
1- A Yagi antenna, also known as a Yagi-Uda array or simply a Yagi, is
a unidirectional antenna commonly used in communications when a
frequency is above 10 MHz This type of antenna is popular among
Amateur Radio and Citizens Band radio operators. It is used at some
surface installations in satellite communications systems.
Yagi Antenna
6
Type of antenna
•
2 - isotropic antenna
•
•
Radiates power equally in all directions
3 - Dipole antennas
•
•
Half-wave dipole antenna (or Hertz antenna)
Quarter-wave vertical antenna (or Marconi antenna):
The term "Marconi antenna" usually refers to a two part
antenna consisting of a vertical portion and
a "reflective" or "ground" portion.
•
•
4 -Parabolic Reflective Antenna
5-Slot antenna
monopole antenna
• 6-monopole antenna: is a radio antenna that is one half
of a dipole antenna combined with a right-angle ground plane
of considerable length in place of its other half.
horn antenna
• -7 horn antenna: is used for the transmission and
reception of microwave signals. It derives its name from the
characteristic flared appearance. The flared portion can be
square, rectangular, or conical.
helical antenna
• - 8- helical antenna is a specialized antenna that
emits and responds to electromagnetic filed with rotating
(circular)polarization. These antennas are commonly used
at earth-based stations in satellite communications
systems. This type of antenna is designed for use with an
unbalanced feed line such as coaxial cable.
Antenna functions
• Transmission line
•
Power transport medium - must avoid power reflections,
otherwise use matching devices
• Radiator
•
Must radiate efficiently – must be of a size comparable with the
half-wavelength
• Resonator
•
Unavoidable - for broadband applications resonances must be
attenuated
Reflector antennas
• Reflectors are used to concentrate flux of EM energy
radiated/ received, or to change its direction
• Usually, they are parabolic (paraboloical).
• The first parabolic (cylinder) reflector antenna
was used by Heinrich Hertz in 1888.
Reflector antennas
• Large reflectors have high gain and directivity
• Are not easy to fabricate
• Are not mechanically robust
• Typical applications: radio telescopes, satellite
telecommunications.
Planar reflectors
d
2d
Uda-Yagi, Log-periodic antennas
•
• Intended reflector antenna
allows maintaining radio link in
non-LOS conditions (avoiding
propagation obstacles)
• Unintended antennas create
interference
14
Receiving antenna equivalent circuit
Radio wave
Transm.line
Receiver
The antenna with the transmission line is
represented by an (The venin) equivalent generator
Rr
Rl
Antenna
jXA
jXL
The receiver is represented by its input impedance as
seen from the antenna terminals (i.e. transformed by
the transmission line)
RL
VA is the (induced by the incident wave) voltage at
the antenna terminals determined when the antenna
is open circuited
VA
Thevenin equivalent
15
Power transfer
1
PA / PAmax
• The maximum power is
delivered to (or from) the
antenna when the antenna
impedance and the
impedance of the
equivalent generator (or
load) are matched
0.5
0
0.1
1
10
RA / RG; (XA+XG = 0)
16
17
Exercise
Exercise
18
Property of R Struzak
19
20