WAVE PROPAGATION
DEFINATION:
~Wave propagation means how waves travel from one place to another.
Waves can be like sound or light, and they move energy through air,
water, or even space.
Categorization of wave:
~The wave can be categorized into two types. They
are:
1.Guided wave
2.Unguided wave
1.Guided wave:
~Guided waves are waves that travel along a specific path or medium, like
through a wire, optical fiber, or along the surface of a solid.
~There are four types of Guided Media which are as follows:
-Open wire
-Twisted pair
-Coaxial Cable
-Optical Fibre
2.Unguided wave:
~Unguided waves are waves that travel freely without being confined
to a specific path or medium. They can spread out in all directions, like
light traveling through the air or radio waves traveling through space.
~There are three types of Unguided transmission media which are as
follows:
-Microwave transmission
-Radio transmission
-Infrared transmission
GENERAL CLASSIFICATION OF WAVES:
1.Plane wave:
~A plane wave is like a perfectly flat wave that travels in a straight line
without bending or spreading out.
2. Uniform plane wave:
~A uniform plane wave is a wave that maintains the same strength and
shape as it travels through a medium or space. It doesn't fluctuate or
change in any noticeable way as it moves forward.
3.Slow wave:
~A wave in which phase velocity is less than velocity of light.
4.Forward wave:
~A forward wave is a wave that travels in the intended direction
without bouncing back.
5.Backward wave:
~A backward wave is a wave that travels in the opposite direction of
the intended path or direction.
6.Standing wave:
~The wave with a combination of forward wave and backward wave.
7.Travelling wave:
~A wave propagating in one direction without any reflection.
8.Surface wave:
~The waves which propagates to the receiving antenna through the
reflections.
MODES OF WAVE PROPAGATION:
• When the transmitting antenna radiates electromagnetic wave, it
takes different paths to reach the receiving antenna.
• The 3 basic paths that the radio signal can follows is,
1.Ground wave propagation
2.Sky wave propagation
3.Space wave propagation
1.Ground wave propagation:
~In this propagation, the signal i.e., Electromagnetic wave
propagates along the ground. It is also known as Surface wave.
~In this propagation both the transmitting and receiving antenna
must be close to the earth.
~It is utilized for short range communication. Because, when a wave is
propagated from transmitting antenna to receiving antenna there will
be an induced signal with respect to the earth.
Maximum
attenuation by
the earth
~As the distance increases between the transmitting antenna to
receiving antenna then the signal strength decreases very fast due to
attenuation by earth. Because of this reason the Ground wave
propagation is utilized for short range communication.
~It is used for Low frequency operation.
~It is used up to 2MHZ only.
~The ground wave is classified as two waves. They are:
-Direct waves
-Surface wave
~The ground wave is a vertically polarized wave. That travels
parallel to the surface of earth.
~For the ground wave propagation vertical antenna are used to
generate vertical polarized wave.
Plane earth reflections:
h1
h2
~If earth is considered as a perfect conductor with infinite
conductivity, then incident and reflected waves have the same
amplitudes.
~If surface of earth is smooth with finite conductivity, then the
amplitude and phase of reflected wave can be obtained by using the
concept of reflection.
~If surface of earth is rough, then the scattering of reflected wave
takes place and amplitude of reflected wave decreases.
~this roughness of the surface which is responsible for the scattering
of reflected wave can be obtained by
If R<0.1 Smooth surface
R>0.1 Rough surface
Field strength of ground wave:
~By solving the Maxwell’s equation we can obtain the field strength
of a ground wave.
Space wave(direct) and surface wave:
~The ground wave field strength can be divided into two parts. They are,
Space wave and Surface wave.
~The space wave dominates at larger heights from earth.
~The surface wave dominates near the surface of earth.
~The space and surface wave expression can be written as,
Wave tilt:
~Consider a transmitting antenna and receiving antenna, which
produces an wavefronts i.e., wavefronts are EM waves.
~As the wavefronts are obstructing the earth surface spontaneously, the
earth surface absorbs the energy of wavefronts.
~Due to this the wavefront signal strength decreases, as the result the
lower part of the wave is bend a little forward. So, this bending of wave
is called as “wavewtilt”. And the angle formed by the bending of wave
is called “Tiltangle”.
~Wave tilt occurs at the surface of earth.
~The tilt depends upon the conductivity and permittivity of the earth.
~It causes power dissipation.
~Due to tilt, both horizontal and vertical components of electric field
exist. These two components are not in phase.
