1. CSC 4315
(WIRELESS NETWORKS AND
PROTOCOLS)
LECTURE 4
Department of Maths and Computer-
Science
Faculty of Natural and Applied Science
BY
DR. BABANGIDA ALBABA
AND
UMAR DANJUMA MAIWADA
2. ANTENNAS
An antenna is an array of conductors (elements),
electrically connected to the receiver or transmitter.
Antennas can be designed to transmit and receive radio
waves in all horizontal directions equally (omnidirectional
antennas), or preferentially in a particular direction
(directional or high-gain antennas).
An antenna is the interface between radio waves
propagating through space and electric currents moving
in metal conductors, used with a transmitter or receiver.
Antennas are required by any radio receiver or transmitter
to couple its electrical connection to the electromagnetic
field. Radio waves are electromagnetic waves which carry
signals through the air (or through space) at the speed of
light with almost no transmission loss.
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4. ANTENNA BASICS
Antenna is a device that propagates EM waves
from a Transmitter, and detects EM waves at a
Receiver.
At the transmitter, a high frequency alternating
current (AC) is supplied to the antenna's terminals,
which radiates (or propagates) the electrical energy
into the air as EM waves. At the receiver, some of
the power of the EM wave is intercepted in order to
produce a tiny AC (or voltage) at its terminals,
which is passed to the internal circuit of the
antenna.
Four important antenna parameters are:
Radiation Pattern
Antenna Efficiency
Antenna Gain
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6. ANTENNA RADIATION PATTERN
Radiation pattern defines the variation of the power radiated
by an antenna as a function of the direction away from the
antenna. A pattern is Isotropic if the radiation pattern is
exactly the same in all directions. However, antennas with
isotropic radiation patterns don't exist in practice.
Omnidirectional antennas radiate out waves in all
directions i.e. they are designed to resemble ‘isotropic
antennas’. Examples of omnidirectional antennas include the
dipole antenna and the slot antenna.
Directional antennas typically have a single peak direction
in the radiation pattern i.e. the direction where the bulk of the
radiated power travels.
Examples include the dish antenna and the slotted
waveguide
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10. ANTENNA EFFICIENCY
Antenna Efficiency is a ratio of the power radiated from the
antenna relative to the power input to the antenna. A high
efficiency antenna has most of the power present at the
antenna's input radiated away. A low efficiency antenna has
most of the power absorbed as losses within the antenna, or
reflected away due to impedance mismatch. The efficiency is
the same whether we are using the antenna as a transmit or
receive antenna. This is known as Antenna Reciprocity.
Antenna Efficiency εR = PR / PI, where
PR = Power radiated from the Antenna,
PI = Power input to the Antenna
Being a ratio, antenna efficiency is a number between 0 and 1.
However, antenna efficiency is commonly quoted in terms of a
percentage; for example, an efficiency of 0.5 is the same as
50%. Antenna efficiency is also frequently quoted in decibels
(dB); an efficiency of 0.1 is 10% or (-10 dB), and an efficiency of
0.5 or 50% is -3 dB. PdB (in Decibels) = 10 Log PW (in Watts)
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11. ANTENNA GAIN
Antenna Gain describes how much power is
transmitted in the direction of peak radiation compared
to that of an isotropic source. It applies to directional
antennas.
A directional antenna with a gain of 3 dB means that the
power received far from the antenna will be 3 dB higher
than what would be received from a lossless isotropic
antenna with the same input power. Similarly, a receive
antenna with a gain of 3 dB in a particular direction
would receive 3 dB more power than a lossless
isotropic antenna.
Antenna Gain G = εRD, where
εR = Antenna Efficiency,
D = Antenna Directivity
Note: 10 dB means 10 times the energy relative to
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12. ANTENNA BANDWIDTH
Antenna Bandwidth is the range of frequencies (or
wavelengths) over which it works effectively. The
broader the bandwidth, the greater the range of different
EM waves you can pick up. That is helpful for something
like television, where you might need to pick up many
different channels, but much less useful for cellular or
satellite phone where all you're interested in is a very
specific radio wave transmission on a fairly narrow
frequency band.
In terms of antenna length, a single antenna can't pick
up two different wave signals if their wavelengths are
very wide apart. This is because it is the wavelength (or
frequency) of the radio waves you are trying to detect
that determines the length of the antenna you need to
use. As a basic rule, the length of the antenna has to be
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