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Lec 12a

The document discusses half-wave dipole antennas including their electric and magnetic field components, average power density, radiation intensity, and radiation resistance. It also provides examples of calculating available power and power density for receiving dipoles located at different angles from a transmitting dipole.

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79 views3 pages

Lec 12a

The document discusses half-wave dipole antennas including their electric and magnetic field components, average power density, radiation intensity, and radiation resistance. It also provides examples of calculating available power and power density for receiving dipoles located at different angles from a transmitting dipole.

Uploaded by

saeednasr521
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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antennaLECTURES

ANTENNA lecture: antenna


BY Abdulmuttalib A. H. Aldouri parameters
& Mohammed Kamil

4. Half-Wave Dipole ( ⁄ )
One of the most commonly used antennas is the half-wavelength (l = λ/2) dipole.
Because its radiation resistance is 73Ω, which is very near the 75Ω characteristic impedances
of some transmission lines.
The electric and magnetic field components of a half-wavelength dipole can be obtained by
letting l = λ/2, thus:

( )
[ ]

( )
[ ]

The average power density and radiation intensity can be written, respectively, as:

( )
[ ]

( )
[ ] ( )

( )
( ) [ ]

* ( )+
∫

( ) ( )

and the radiation resistance is:

( )

( )

9
antennaLECTURES
ANTENNA lecture: antenna
BY Abdulmuttalib A. H. Aldouri parameters
& Mohammed Kamil

To find the HPBW:

( )
( )| [ ]

( )

( ) ( ( ))

By using trial and error, we can find the value of θh 51o

| | | |

Figure (13) shows the two and three dimensional radiation pattern for a λ/2 dipole.

0
330 30

300 60

1
0.5
270 90

240 120

210 150
180

Figure (13)

H.W. For a λ/4 dipole:


1. Find the radiation resistance.
2. Maximum directivity and maximum aperture.
3. HPBW and FNBW.
4. Draw the radiation pattern.

10
antennaLECTURES
ANTENNA lecture: antenna
BY Abdulmuttalib A. H. Aldouri parameters
& Mohammed Kamil

Example:
A λ/2 dipole radiates a time-averaged power of 600 W at a frequency of 300 MHz. A second
λ/2 dipole is placed at a point ( ), where r = 200 m, = 90◦, = 40◦. It is oriented
so that its axis is parallel to that of the transmitting antenna. What is the available power at the
terminals of the second (receiving) dipole?
Solution:

( )

( )

( ) 1.643

( )

H.W: Find prad at r = 200 m, = 50◦, = 20?

Example:
A dipole is radiating into free-space. Input power to the dipole is 100 W. Assuming an
overall efficiency of 50%, find the power density (in W/m2) at (r = 500 m, = 60◦, = 0)?
Solution:

11

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