folded dipole anteena
TRANSCRIPT
-
7/30/2019 folded dipole anteena
1/12
FOLDED DIPOLE ANTENNA
-
7/30/2019 folded dipole anteena
2/12
Folded dipole antenna is made with twoor more parallel and closely spaceddipole antennas connected together attheir ends with one of dipole antennacentre fed.
The basic dipole can be /\/2 long butfolded structures shows that it forms a
complex circuit. It is the heart of many advanced antenna
designs because it is mechanically morerugged than a simple dipole and
bandwidth is about 10% greater then the
-
7/30/2019 folded dipole anteena
3/12
The size of the dipole antenna is morebut gain and directivity is less, so if the
dipole antenna is folded and length afterfolding is /\/2,than its size is reducedand radiation performance improves.
As the no. of dipole elements increase
the impedance radiation efficiencyincreases. In the folded dipole antenna,when one element is center fed thenother elements are inductively coupled
and transfer the radiation from one dipoleto adjacent dipole and amplify theradiation. As the no. of dipoles increases,the gain & directivity increases.
-
7/30/2019 folded dipole anteena
4/12
Z=73
SIMPLE DIPOLE
-
7/30/2019 folded dipole anteena
5/12
Z=273
FOLDED DIPOLE WITH TWO
ELEMENTS
FOLDED DIPOLE WITH THREE
ELEMENTS
Z=373
-
7/30/2019 folded dipole anteena
6/12
RANGE-HF,VHF,UHF,Range.
Structure
1.it is a single antenna but consist ofmore elements .
2.The spacing between the arms is very
small and is of order of /\/100.3.When the power is fed through first
then second is inductively coupled at
ends.
DESIGN-
If the folded dipole consist of n parallel
and closely spaced dipoles the
impedance -
-
7/30/2019 folded dipole anteena
7/12
-
7/30/2019 folded dipole anteena
8/12
-
7/30/2019 folded dipole anteena
9/12
V/2=IZ+IZ
WHEN ICurrent in dipole 1
ICurrent in dipole 2ZSelf impedance of dipole
1.
ZMutual impedance
between 1&2.if I= I=I for equal dimensions
V/2=I(Z+Z)
Since two dipoles are very small and spacingis very small Z+Z
V/2=2IZ
Z=V/I=4Z =473 =273
-
7/30/2019 folded dipole anteena
10/12
In the same way for three arm antenna
Z=973=373
So for n arms Z=n73
Bandwidth of folded dipole is 10% which i
greater than simple dipole.
-
7/30/2019 folded dipole anteena
11/12
Advantages
High input impedance Greater bandwidth
Low cost
Television reciever,short distance
communication, radar etc.
Applications
-
7/30/2019 folded dipole anteena
12/12