INNTRODUCTION TO WIRELESS COMMUNICATION Flashcards
fastest growing segment in communication industry
Wireless communication
is the medium in terms of transmission media
Free Space
He developed the first practical radio system and what year?
1895: Guglielmo
Marconi
Marconi successfully transmitted the first transatlantic signal
1901
The first radio broadcast was made
1906
The concept of cellular telephony was introduced
1947
He made the world’s first handheld cellular phone call and what year?
1973: Martin Cooper
Nordic Mobile
Telephone (NMT), the first fully operational cellular network, was launched.
1981
The first version of the Wi-Fi standard (802.11) was released
1997
802.11g standard were introduced, offering speeds up to 54 Mbps.
2003
The 802.11n standard were introduced, allowing speeds of up to 600 Mbps.
2009
The introduction of 4G networks brought download speeds of up to 100 Mbps
2009
The deployment of 5G networks began, promising speeds up to 10 Gbps, ultra-low latency, and enhanced capacity for a wide range of applications.
2018
laid the foundation for
wireless communication systems, transforming the way
information is transmitted.
development of radio waves
enabled mobile
communication, making it possible to connect with
others while on the move.
introduction of cellular networks
revolutionized internet connectivity,
allowing
Wi-Fi technology
have opened up new possibilities
for high-speed connectivity, enabling advanced
applications and services.
4G and 5G networks
It was predicted
mathematically by
James C. Maxwell in
1865
demonstrated
experimentally the radio wave propagation
Heinrich R. Hertz in
1867.
Free-space propagation of electromagnetic waves is often
called
radio-frequency (RF) propagation or simply radio
propagation.
are electromagnetic waves, like light, that
propagates through free space in a straight line with a
velocity of approximately same as speed of light.
Radio waves
Once a radio signal has been radiated by an antenna, it —————————————-
through space and ultimately
reaches the receiving antenna.
travels or propagates
The energy level of the signal ——– rapidly with
distance from the transmitting antenna ——–.
decreases , increases
is affected by objects that it
encounters along the way such as trees, buildings, and
other large structures.
electromagnetic wave
The path that an electromagnetic signal takes to a
receiving antenna depends upon many factors, including
the
frequency of the signal, atmospheric conditions, and
time of day.
is an electrical energy that has escaped into free space.
ELECTROMAGNETIC WAVE
as the name implies,
involves the creation of electric and magnetic fields in
free space or in some physical medium.
Electromagnetic radiation
The waves that propagate are known as
transverse
electromagnetic waves (TEM).
characteristically means that the electric field, the
magnetic field and the direction of propagation of the
wave are all mutually perpendicular.
TRANSVERSE ELECTROMAGNETIC WAVE
The essential properties of radio waves are
frequency,
intensity, direction of travel, propagation velocity,
and plane of polarization.
What are the properties of electromagnetic waves?
transverse electromagnetic wave &
Longitudinal
one direction
directional
all directions
omnidirectional
free space does not have losses
TRUES
Types of plane of polarization
Linear, Circular, Elliptical
The —————– of a plane electromagnetic wave is
simply the orientation of the electric field vector in respect
to the surface of the earth (looking at the horizon).
polarization
If the polarization remains constant, it is described as
Linear Polarization.
The two forms of linear polarization are
horizontal and vertical.
If the electric field is propagating parallel to the Earth’s
surface, the wave is said to be
horizontally polarized.
If the electric field is propagating perpendicular to the
Earth’s surface, the wave is said to be
vertically
polarized.
If the polarization vector rotates 360 ̊ as the wave moves
one wave length through space and the field strength is
equal at all angles of polarization, the wave is described
as having
Circular Polarization.
When the field strength varies with changes in
polarization, this described as
Elliptical Polarization.
The speed of propagation of radio waves in free space is
the same as that of light, approximately 300 x 106 m/s. In
other media, the velocity is lower. The propagation
velocity is given by vp =
c/εr
PROPAGATION VELOCITY
is the ratio
of permittivity of the material and the permittivity of air
or free space. The permittivity of air is approximately 8.85
x 10-12 F/m
εr =ε/εo
Relative permittivity (dielectric constant)
For a given length of RG 8A/U coaxial cable using a
material with a permittivity of 20.3646 x 10-12 F/m as
dielectric, determine the velocity of propagation of the
wave travelling through it.
ANS. 1.99 x 108 m/s
Find the wave’s velocity in a coaxial cable using a solid
polyethylene with a dielectric constant of 5.3.
1.30 x 10 ^8 m/s
Find the propagation velocity of radio waves in glass
with a relative permittivity of 7.8.
1.07 x 10 ^8 m/s
The simplest source of electromagnetic waves would be a
point in space.
POWER DENSITY
would radiate equally from this source in all
directions.
Waves
A ——–, that is, a surface on which all the
waves have the same phase, would be the surface of a
sphere.
wavefront
Such a source is called an
isotropic radiator
There is no loss of energy as radio waves propagate in
free space, but there is attenuation due to the spreading
of the waves.
POWER DENSITY
The energy would be spread over a larger surface as the
distance from the source
increased.
Since an isotropic radiator radiates equally in all
directions, the —————, in watts per square meter,
is simply the total power divided by the surface area of
the sphere. PD =
Pt/4πr^2
POWER DENSITY
As the wavefront moves further from the source, the
——- the power density. It is seen that power density is
inversely proportional to the square of the distance from
the source. This is the ——–, which applies
universally to all forms of radiation in free space.
smaller, inverse-square law
is also the rate at which the energy passes
through a given surface area in free space
PD = εH
Power density
The strength of the electric field, ε (in volts per meter), at a
distance r from a point source is given by
ε =sqrt30Pt/r
CHARACTERISTIC IMPEDANCE OF FREE SPACE
are related to impedance
in the same way that power and voltage relate in an electric
circuit.
PD =ε^2/Zo
Power density and the electric field
of a lossless transmission medium
is equal to the square root of the ration of its magnetic
permeability to its electric permittivity.
Zo =sqrtμ/ε
Characteristic Impedance
the characteristic impedance of free space is
377Ω
For an isotropic antenna radiating 100 W of power,
determine: (a) power density 1000m from the source and
(b) power density 2000m from the source
ANS. (a) 7.96 μW/m2 (b) 1.99 μW/m2
The dielectric strength of air is about 3MV/m. arcing is
likely to take place at field strengths greater than that. What
is the maximum power density of an electromagnetic wave
in air?
ANS. 23.9 GW/m2
Free space is a vacuum, so no loss of energy as a wave
propagates through it. As waves propagates through free
space, however, they spread out, resulting in a reduction
in power density.
ATTENUATION
The reduction in power density with
distance is equivalent to a power loss and is commonly
called
wave attenuation
Because the attenuation is due to the spherical spreading
of the wave, it is sometimes called
space attenuation.
is generally expressed in terms of the
common logarithm of the power density ratio.
α = 10log
(PD1/PD2)= 10log(
(r2/r1)^2
Wave attenuation
Earth’s atmosphere is not a vacuum, it contains particles
that can absorb electromagnetic energy.
ABSORPTION
As an
electromagnetic wave passes through the atmosphere, it
interchanges energy with free electrons and ions. This
type of reduction of power is called
absorption loss.
If the ions do not collide with gas molecules or other
ions, all the energy is converted back into
electromagnetic energy, and the wave continues
propagating with no loss of intensity.
ABSORPTION
However, if the ions collide with other particles, they
dissipate the energy that they have acquired from the
electromagnetic wave, resulting in
absorption of the
energy.
Since the absorption of energy is dependent on the
collision of particles, the greater the particle density, the
greater the possibility of collisions and the greater the
absorption
ABSORPTION
The electromagnetic energy is absorbed and scattered by
the ———- and this effect becomes more pronounced
when the length of the wave approaches the size of the
rain drop.
raindrops
the reduction in power density due to inverse
square law presumes free-space propagation is called
wave attenuation.
The reduction in power density due
to non free-space propagation is called
absorption.
The figure shows atmospheric absorption split into its
two major components, with absorption due to the water
vapor content of the atmosphere taken for a standard
value of humidity.
* If humidity is ——– or if there is fog, rain or snow,
then this form of absorption is ——–tremendously,
and reflection from rainwater drops may even take place.
increased , increased
causes severe absorption at microwave
frequencies
Precipitation
In Earth’s atmosphere, ray-wavefront propagation may
be altered from free-space behavior by optical effects
such as
refraction, reflection, diffraction and
interference.
Using rather unscientific terminology, refraction can be
thought of as ——, reflection as ——,
diffraction as —— and interference as ——..
bending, bouncing, scattering, colliding
It is sometimes referred to as the bending of the radio-
wave path. However, the ray does not actually bend.
REFRACTION
is actually the changing of
direction of an electromagnetic ray as it passes obliquely
from one medium into another with different velocities
of propagation.
Electromagnetic refraction
The velocity of propagation at which an electromagnetic
wave propagates is inversely proportional to the density
of the medium in which it is propagating.
REFRACTION
can be expressed in
terms of refractive index of the atmosphere it is passing
through. Mathematically, it is the square root of the
dielectric constant.
n = sqrtεr
Refraction of electromagnetic waves
The amount of bending or refraction that occurs at the
interface of the two materials of different densities
depends on the refractive index of the two materials.
is simply the ratio of the velocity of
propagation of a light ray in free space to the velocity of
propagation of a light ray in a given material.
Mathematically,
n =c/vp
refractive index
Vacuum
1.0
Air
1.0003 (1)
Water
1.33
Ethyl Alcohol
1.36
Fused quartz
1.46
Glass Fiber
1.5-1.9
Diamond
2.0-2.42
Silicon
3.4
GALLIUM ARSENIDE
2.6
The relationship between the angles and the indices of
refraction is given by a formula known as
Snell’s law:n1sinθi = n2sinθr
And because the refractive index of a material is equal to
the square root of its dielectric constant
sinθi/sinθr=sqrtεr/εi
In extreme cases, where the angle of incidence is large
the wave travels into a region of considerably lower
dielectric constant,———————, so that the wave comes out of the second
medium and back into first.
the angle of refraction can be greater
that 90 ̊
For these, refraction becomes a form of reflection called
total internal reflection.
is the angle of incidence that results in an
angle of refraction of exactly 90 ̊ and it is given by θc = sin−1(n2/n1)
Critical angle
A radio signal moves from air to glass. The angle of
incidence is 20 ̊. Calculate the angle of refraction.
ANS. 13.1839 degree
Find the critical angle when a wave passes from glass,
into air.
ANS. 41.8245 degree
occurs when an incident
wave strikes a boundary of two media and some or all of
the incident power does not enter the second material.
The waves that do not penetrate the second medium are
reflected.
Electromagnetic reflection
Saying all the reflected waves remain in medium 1, the
velocity of the reflected and incident waves are ——. The angle of reflection equals to the angle of incidence.
equal.
However, the reflected voltage intensities is less than the
incident voltage ———
field intensity.
The ratio of the reflected and incident power densities is
called
reflection coefficient (Γ)
The portion of the total incident power that is not
reflected is called the ——–. For a perfect conductor, T = ?.
power transmission coefficient
(T).
T = 0
The fraction of power that penetrates medium 2 is
absorption coefficient.
When an incident wavefront strikes an irregular surface, it
is randomly scattered in many directions. Such condition
is called
diffused reflection
Whereas reflection from a perfectly smooth surface is
called
specular (mirrorlike) reflection.
Surface that fall between smooth and irregular is called
semi-rough surfaces.
states that a semi-rough surface will
reflect as if it were a smooth surface whenever the cosine
of angle of incidence is greater than λ/8d, where d is the
depth of irregularity.
cos θi ≥λ/8d
Rayleigh criterion
is the bending of waves around an object.
Diffraction
is defined as the modulation or redistribution
of energy within a wavefront when it passes near the
edge of an opaque object.
Diffraction
is the phenomenon that allows light or radio
waves to propagate (peek) around corners.
Diffraction
Diffraction is explained by Huygen’s principle presented
by Dutch astronomer, —–, the founder of the wave theory of light.
Christian Huygens
states that every point on a given
spherical wavefront can be considered as a secondary
point source of electromagnetic waves from which the
other secondary waves are radiated outward.
Huygen’s principle
As the wave front passes the object, the point sources of
waves at the edge of the obstacle create additional
spherical waves that penetrate and fill in the ——. This phenomenon, sometimes called,
shadow
zone, knife-edge
diffraction.
result from the superposition of
oscillations or waves of same nature and equal
frequency.
Interferences
These ———- can be either constructive when the
different paths arrive in phase, leading to a signal
reinforcement, or destructive, causing in this case a
fading of the signal.
interferences
After a wave has been emitted, a wave may follow
different paths between the ——————- .
emitter and the receiver
This results in a multitude of elementary paths. Each such
path is characterized at receiver level by an
attenuation, a
delay and a specific phase difference.
This mode of propagation is referred to as a ———-. The different waves propagated along
such multiple paths interfere at the reception.
multipath
propagation.
Which of the following statements about a wave is the law
of reflection?
a. The angle of incidence is equal to the refracted wave
b. The angle of incidence is not equal to the refracted wave
c. The angle of incidence is equal to the angle of reflection
d. The angle of incidence is not equal to the angle of
reflection
c. The angle of incidence is equal to the angle of reflection
If a wave passes first through a dense medium and then
through a less dense medium, which of the following angle
of refraction conditions exists?
a. The angle of refraction is greater than the angle of
incidence
b. The angle of refraction is less than the angle of incidence
c. The angle of incidence is equal to the angle of reflection
d. The wave will pass through in a straight line
a. The angle of refraction is greater than the angle of
incidence
The electric field and magnetic field combine to form which
of the following types of waves?
a. Spherical wave
b. Elliptical wave
c. Electromagnetic wave
d. Kamehameha wave
c. Electromagnetic wave
The “attenuation of free space” is due to:
a. Losses in characteristics impedance of free space
b. Losses due to absorption in the upper atmosphere
c. The decrease in energy per square meter due to
expansion of the wavefront
d. The decrease in energy per square meter due to
absorption of the wavefront
c. The decrease in energy per square meter due to
expansion of the wavefront
Diffraction of electromagnetic waves
a. is caused by reflections from the ground
b. arises only with spherical wavefronts
c. will occur when the waves pass through a large slot
d. may occur around the edge of a sharp obstacle
d. may occur around the edge of a sharp obstacle
- At 20 km in free space from a point source, the power
density is 200 μW/m2. What is the power density
25 km away from this source?
ANS. 128 μW/m2
- An isotropic source radiates 100 W of power in free
space. At a distance of 15 km from the source, calculate the
power density and the electric field intensity.
ANS. 35.37 nW/m2
- Light travels from air into an optical fiber with an index of
refraction of 1.44. If the angle of incidence on the end of
the fiber is 22o, what is the angle of refraction inside the
fiber?
ANS. 15.12 degree
