wireless networking radio frequency and antenna fundamentals module-02 jerry bernardini community...
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Wireless Networking
Radio Frequency and Antenna Fundamentals
Module-02
Jerry BernardiniCommunity College of Rhode Island
04/18/23 Wireless Networking J. Bernardini 1
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Presentation Reference Material• CWNA Certified Wireless Network
Administration Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett– Chapter-2, pp.35-65
• The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project
04/18/23 Wireless Networking J. Bernardini 2
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Radio and the Electromagnetic Spectrum
• Radio frequencies are part of the electromagnetic spectrum
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Early Radio
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•1895 Marconi was not the first•1906 Reginald Fessenden , 11 miles lad to sea•1927 First transatlantic telephone•1924 Bell Labs two-way voice carrying radio•Radio first used for voice and broadcast•Then used by military
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Radio Frequency
• Radio frequency, (RF) is a term that refers to alternating current, (AC) having characteristics such that, if the current is input to an antenna, an electromagnetic (EM) field/wave is generated suitable for wireless communications.
AC Signal
Transmission Line Antennaand
Tower
EM Wave
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EM Waves
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•Electromagnetic waves are made up of electric wave and magnetic waves at right angles
•The wave moves at right angle to the electric and magnetic waves
•In a vacuum the wave moves at the speed of light (3x108 meter/sec)
•Electric field is the force on an electric charge
•A moving electric field will produce a moving magnetic field, which produces a moving electric field, ad infinitum
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Sine Wave CycleA
mp
litu
de
Time
1 Cycle
Period,
F = 1
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RF Properties
• Amplitude - The amount of a signal. Amplitude is measured by determining the amount of fluctuation in air pressure for sound or the voltage of an electrical signal.
Amplitude
Time
Waveform A
Waveform B
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RF Properties
• Frequency -The number of repetitions per unit time of a complete waveform, measured in Hertz. The number of complete oscillations per second of electromagnetic radiation.
Amplitude
Time
= Period
F = 1/
A
B
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RF Properties
• Wavelength, -The distance that a wave travels in the time it takes to go through one full 360 degree phase change, or one cycle.
Amplitude
Distance
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Wavelength
1 Wavelength,
= 300,000,000 m/sFrequency (Hz)
= 984,000,000 f/sFrequency (Hz)
In a Vacuum
= 300,000,000 m/s2.45 GHz
= 0.122 m = 12.2 cm
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RF Properties
• Phase, - Time based relationship between a periodic function and a reference. In electricity, it is expressed in angular degrees to describe the voltage or current relationship of two alternating waveforms.
Amplitude
Time0
Unit Circle
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RF Properties• Polarization – By convention the orientation of
the electric field, (E) with respect to the earth’s surface. Vertical, Horizontal, and Circular/Elliptical polarization.
P
HE
E
EE
A B C D
E
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RF Properties• Polarization – By convention the orientation of
the electric field, (E) with respect to the earth’s surface. Vertical, Horizontal, and Circular/Elliptical polarization.
A B C
Earth/Ground Reference
D E
Ceiling
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RF Spectrum
Designation Abbreviation Frequencies
Ultra High Frequency
UHF 300 MHz - 3 GHz
Super High Frequency
SHF3 GHz - 30 GHz
Very Low Frequency -
Extremely High Frequency
VLF - EHF 9 kHz – 300 GHz
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US Frequency Allocation Chart
• National Telecommunications and Information Administration. http://www.ntia.doc.gov/osmhome/allochrt.html
9 kHz 300 GHz
802.11a, b, g
AMRadio
FMRadio
535-1605kHz
88-108MHz
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Amplification and Attenuation
• Amplification/Gain - An increase in signal level, amplitude or magnitude of a signal. A device that does this is called an amplifier.
• Attenuation/Loss - A decrease in signal level, amplitude, or magnitude of a signal. A device that does this is called an attenuator.
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Amplification / Gain
100 mW
RF Amplifier
1 W
SignalSource
AntennaINPUT
OUTPUT
The power gain of the RF amplifier is a power ratio.
Power Gain = = = 10 no unitsPower Output
Power Input
1 W
100 mW
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Attenuation / Loss
100 mW
RF Attenuator
50 mW
SignalSource
AntennaINPUT
OUTPUT
The power loss of the RF attenuator is a power ratio.
Power Loss = = = 0.5 no unitsPower Output
Power Input
50 mW
100 mW
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Attenuation of an EM wave• Attenuation/Loss - A decrease in signal level,
amplitude, or magnitude of a signal.
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Parameters & Units of Measure
• Power - The rate at which work is done, expressed as the amount of work per unit time.
• Watt - An International System unit of power equal to one joule per second. The power dissipated by a current of 1 ampere flowing between 1 volt of differential.
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EIRP
Access Point
Point A Point B
Parabolic Antenna
Point C
Point A – Output of AP
Point B – Intentional Radiator
Point C – Radiated wave from antenna (transducer)
Effective Isotropic Radiated Power
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Voltage Standing Wave Ratio
• VSWR - is a measure of how well the components of the RF system are matched in impedance. VSWR is the ratio of the maximum voltage to the minimum voltage in a standing wave. For maximum power transfer the ideal VSWR is 1.
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Voltage Standing Wave Ratio50
50
50
Output impedance of AP is 50 Impedance of cable is 50 Input impedance of antenna is 50
The impedances are matched so the VSWR = 1
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Basic Properties of EM waves• Reflection – cast off or turn back, (bouncing).
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Basic Properties of EM waves
• Refraction - deflection from a straight path, (bending through a medium).
Earth
Atmosphere
Refracted Wave Path
Straight-Line Wave PathSky Wave
Antenna
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Basic Properties of EM waves• Diffraction – Change in the directions and
intensities of a group of waves when they pass near the edge of an EM opaque object, (bending around object).
Transmitter Receiver
Bui
ldin
g
ShadowZone
Diffracted Signal
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Basic Properties of EM waves• Interference - hinders, obstructs, or impedes.
When two or more wave fronts meet, (colliding).
Direct WaveMultipathInterferenceReflected Wave
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Basic Properties of EM waves• Scattering – A specification of the angular
distribution of the electromagnetic energy scattered by a particle or a scattering medium, (dispersion).
Incident Wave
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Basic Properties of EM waves• Absorption – The process in which incident
radiant energy is retained by a substance by conversion to some other form of energy.
Incident WaveDrywall
Concrete