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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
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
Radio and the Electromagnetic Spectrum
• Radio frequencies are part of the electromagnetic spectrum
04/18/23 Wireless Networking J. Bernardini 3
Early Radio
04/18/23 Wireless Networking J. Bernardini 4
•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
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
EM Waves
04/18/23 Wireless Networking J. Bernardini 6
•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
Sine Wave CycleA
mp
litu
de
Time
1 Cycle
Period,
F = 1
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
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
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
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
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
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
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
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
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
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.
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
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
Attenuation of an EM wave• Attenuation/Loss - A decrease in signal level,
amplitude, or magnitude of a signal.
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.
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
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.
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
Basic Properties of EM waves• Reflection – cast off or turn back, (bouncing).
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
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
Basic Properties of EM waves• Interference - hinders, obstructs, or impedes.
When two or more wave fronts meet, (colliding).
Direct WaveMultipathInterferenceReflected Wave
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
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
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