Introduction to Antennas and Radiating Systems
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Transcript of Introduction to Antennas and Radiating Systems
Introduction to Antennas & Radiating Systems
Austin Peay State University
William CookeDepartment of Physics & Astronomy
J. Caleb WherryDepartment of Computer Science
Outline
2
I. Introduction
II. What is An Antenna?
i. Transmission Lines
ii. Free Space
iii. The Antenna
III. How An Antenna Works
i. Radiating from Accelerating Particles
ii. Electric and Magnetic Fields
iii. Radiation Patterns
IV. The /2 Short Dipole
V. Conclusion
Introduction
3
What is An Antenna?
4
Transmission Line/Guided PathA transmission line is a path in which a current flows. This line can be a
typical circuit, coaxial cable, or any other material with a well-defined, complex impedance.
Free SpaceFree space is made up of fields and void of other matter. These fields carry
energy in the form of waves which can travel freely throughout.
AntennaAn antenna is the interface between the above transmission lines and free
space. It takes the current from the transmission lines and converts it to waves which get transmitted into free space, and vice versa.
How An Antenna Works
5
How An Antenna Works
6
How An Antenna Works
7
Image Source: http://en.wikipedia.org/wiki/Dipole
Field Patterns
8
Field Pattern Lobes
9
HPBW: half power beam width
Power Pattern
10
Main lobe axisMain lobe
Minor lobes
][1
)(0
BES
Back lobes
11
12
)(
0 )]2
(2
sin[)]([ c
rtj
ezL
IzI
Retarded Current distance z away from poles:
z dz
Integrating over all dz’s to get E & H components of far field:
0
coscos[ ] cos( )[ ] 2 2[ ]
2 sin120
L Lj I
Er
H E Z E
13
]sin
)2
cos(]2cos
cos[[
2
][ 0
LL
r
IjE
We can then find the Power by integrating the above field over a large surface of the Poynting vector:
20
2
0 0
2* 30sin IddrHEPrad
0
2
020
230 R
IIPrad
Radiation Resistance:
730R
Conclusion
14
Antennas are all around us! Examples listed here are only a small subset of a rich field of study.
Antennas’ shape are of great importance in the theory of transmission and receiving of antennas (Optimization theory – Genetic Algorithms).
A better understanding of how antennas work gives us an understanding of the electromagnetic radiation into or
out of our electronic device.
Enjoy your summer!
References
15
Griffiths, D.J. Introduction to Electrodynamics. 3rd ed. Prentice-Hall: Upper Saddle River, NJ. 1999.
Kraus, J.D. Antennas. 2nd ed. McGraw-Hill: New York.1988.
Questions &| Comments
16
Questions &| Comments?