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Ugweje WL040/Bidgolio-Vol I WL040-Sample.cls June 19, 2003 17:10 Char Count= 0
180 RADIOFREQUENCY ANDWIRELESSCOMMUNICATIONSTable 1Radio-Frequency Band Classification and CharacteristicsFrequency
Frequency Band Range Propagation Characteristics λρL Typical UseVery low < 30 kHz Low attenuation day and Long Low Long Baseband signals; power line;
frequency (VLF) night; high atmospheric ↑ ↑ home control systems;
noise level. navigation and submarine
communication.
Low frequency 30–300 kHz Slightly less reliable Long-range navigation;
(LF) than VLF; absorption marine communication;
in daytime. radio beacons.
Medium 0.3–3 MHz Attenuation low at Maritime radio; direction
frequency (MF) night, high in day; finding; AM broadcasting.
atmospheric noise.
High frequency 3.0–30 MHz Omni-directional energy International broadcasting,
(HF) radiation; quality varies military communication;
with time of day, season, long-distance aircraft
and frequency. and shipcommunication.
Very high 30–300 MHz Direct and ground waves; VHF TV; FM broadcast; two-
frequency (VHF) cosmic noise; antenna way radio, AM aircraft
design and height communication and
is critical. navigational aids.
Ultra high 0.3–3 GHz LOS; repeaters are used UHF TV; cellular phone;
frequency (UHF) to cover greater distances; radar; microwave links;
cosmic noise. PCS.
Super high 3.0–30 GHz LOS; atmospheric attenuation Satellite and radar
frequency (SHF) due to rain (>10 GHz), communication; terrestrial
oxygen and water vapor. microwave; wireless local
loop.
Extremely high 30–300 GHz LOS; millimeter wave; Experimental; wireless local
frequency (EHF) atmospheric attenuation loop.
due to rain, oxygen and ↓
water vapor. Short High Shortsource (the antenna) at the speed of light with the suc-
ceeding wave front changing in amplitude as the volt-
age or current changes in amplitude. Radio waves propa-
gate through space as traveling EM fields proportional to
the time-varying voltage or current. The propagating RF
energy is composed of an electric field and a magnetic
field component. The two fields exist together because
a change in the electric field generates a corresponding
change in the magnetic field, and vice versa. At the Rx
the antenna performs an inverse operation of converting
a time-varying propagating EM wave to a time-varying
voltage or current.
Polarization of the radio wave is important and is given
by the direction of the electric field component. Usually
the construction and orientation of the antenna determine
the electric field component. Many antennas are linearlyL S C X KU K KA U E F UQ V W P14022204 8 12.4 18 26.5 60 90 14033 50 75 110 170 GHzGHzFigure 2: Typical symbol assignment for RF bands.polarized, either horizontally or vertically. The magnitude
of the power radiated in the direction of propagation can
be calculated as the effective isotropic radiated power
(EIRP) or effective radiated power. This is the maximum
radiated power available from a Tx in the direction of max-
imum gain for isotropic or directional antennas, respec-
tively. It is a measure of the effectiveness of an antenna in
directing the transmitter power in a particular direction
(Rappaport, 2002).Forms of Radio Waves
Radio waves propagate in space in various forms. The
characteristics of the propagating waves are of inter-
est in many wireless communication systems designs.
Propagating radio waves can be classified as direct (or
free space), ground (or surface), tropospheric, and iono-
spheric. These types of waves are illustrated in Figure 3.
Direct waves are the simplest kind of radio waves, in
which propagation is in free space without any obstruc-
tion. They are projected in a straight LOS between the Tx
and Rx. The two-way radio, cellular mobile telephone, and
personal communication system seldom have this type of
radio wave.
Ground waves are confined to the lower atmosphere
or the surface of the earth. A ground wave includes that