Antenna and Wave propagation

1. RADIO WAVE PROPAGATION
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2. The wave propagation
characteristics between
transmitter and receiver are
controlled by the transmitting
antenna, operating frequencies
and media between them.
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3. 3

4. Electromagnetic Radiation
 Radio: cm to km wavelength
 Microwaves: 0.1 mm to cm
 Infrared: 0.001 to 0.1 mm
 Visible light 0.0004 – 0.0007 mm
 Ultraviolet 10-9 – 4 x 10-7 m
 X-rays 10-13 – 10-9 m
 Gamma Rays 10-15 –10-11 m
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5. RADIO WAVES
 Electromagnetic radiation comprises both an Electric and a
Magnetic Field.
 The two fields are at right-angles to each other and the direction
of propagation is at right-angles to both fields.
 The Plane of the Electric Field defines the Polarisation of the
wave.
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z
x
y
Electric
Field, E
Magnetic
Field, H
Direction of
Propagation

6.  When an EM waves is produced by an antenna it
moves from transmitter to the receiver in the following
ways:
A part of the wave travels along or near the
surface of the earth. This wave is called ground wave
or surface wave.
Some waves travel directly from the
transmitting to the receiving antenna called space
waves.
Some waves travel upwards into space towards
the sky and get reflected back to the receiver called
sky waves.
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8. FACTORS INVOLVED IN THE PROPAGATION OF RADIO WAVES
 Earth’s characteristics in terms of conductivity, permittivity and
permeability.
 Frequency of operation.
 Polarization of Tx antenna.
 Height of the Tx antenna.
 Transmitter power.
 Curvature of the earth.(Roughness, magnetic field, type of earth
etc.,)
 Electrical and moisture content in the troposphere.
 Characteristics of ionosphere.
 Refractive index and permittivity of troposphere and ionosphere
regions.
 Distance between the transmitter and the receiver.
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9. GROUND WAVE
 A wave is said to be ground wave or surface wave when
it propagates from transmitter to receiver by gliding
over the surface of the earth.
 It exists when both the transmitting and the receiving
antennas are close to the earth and antennas are
vertically polarized.
 It is useful for communication at VLF, LF and MF.
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10. •Follows contour of the earth
•Can Propagate considerable distances
•Frequencies up to 2 MHz
•Example
•AM radio
GROUND WAVE BETWEEN TRANSMITTING AND RECEIVING ANTENNAS
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11. VERTICALLY POLARISED WAVE
EQUIVALENT CIRCUIT OF THE EARTH
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12. GROUND WAVE FIELD STRENGTH
 According to Somerfield analysis, the ground wave
field strength for flat earth is given by:
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E - Field strength at a point, V/m
Eo - Field strength of the wave at a unit distance
from the transmitting antenna V/m
A - factor of the ground losses
d - distance of the point from transmitting
antenna

13.  Power radiated by the transmitting antenna.
 Directivity of the antenna in vertical and horizontal
planes.
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FACTORS THAT Eo DEPENDS
FACTORS THAT ‘A’ DEPENDS
•Conductivity,
•Permittivity of the earth
•Frequency of the wave
•Distance from the transmitter

14. SALIENT FEATURES
 Ground wave propagates by gliding over the surface of the earth.
 It exists for vertically polarized waves.
 Exists for antennas close to earth.
 Suitable for VLF, LF and MF communications.
 Used at 15 KHz and up to 2 MHz .
 Ground wave field strength varies with characteristics of the earth.
 Requires relatively high transmitter power.
 Not affected by the changes in atmospheric conditions.
 Used to communicate between two points on the globe if there is
sufficient transmitter power.
 Used for radio navigation, ship-to-ship, ship-to-shore communication
and maritime mobile communications.
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15. REFLECTION OF RADIO WAVES BY THE SURFACE OF THE EARTH
 The reflection coefficient is the ratio of the
reflected wave to the incident wave.
 The field strength near the earth is the vectorial
sum of the incident and the reflected fields.
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REFLECTION COEFFICIENT DEPENDS ON:
• Dielectric constant.
• Conductivity of the earth.
• Frequency of the wave.
• Polarization of the wave.
• Angle of incidence of the wave.

16. VARIATION OF ‘ρ Vs θ i’:
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17. BREWSTER ANGLE
 The angle of incidence at which there is no
reflection is known as ‘BREWSTER ANGLE’.
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ROUGHNESS OF EARTH:

18. WAVE TILT OF THE GROUND
 It is defined as the change of orientation of the
vertically polarized ground wave at the surface of the
earth.
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19. SALIENT FEATURES OF WAVE TILT
 Wave tilt occurs at the surface of the earth.
 Depends on conductivity and permittivity of the earth.
 It causes power dissipation.
 Exists both horizontal and vertical components of the
electric field.
 These two components are not in phase.
 Wave tilt changes the originally vertically polarized wave
in to elliptically polarized wave.
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21. 21

22.  Sky wave propagation is also called Ionospheric wave
propagation.
 EM waves directed upward at some angle from the earth’s
surface are called Sky waves.
 Frequency range: 2 to 30 MHz and for long distance
communication.
 Ionosphere is the upper portion of the atmosphere
between approximately 60 Km and 400 km above the
earth which is ionized by absorbing large quantities of
radiation from the sun.
 Ionization is a process by which a neutral atom or
molecule gains or loses electrons and is left with a net
charge
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23. COMPOSITION OF THE ATMOSPHERE
 Nitrogen 78.08%
 Oxygen 20.95%
 Argon 0.93% (9300 ppm)
 Carbon Dioxide 0.035% (350 ppm)
 Neon 18 ppm
 Helium 5.2 ppm
 Methane 1.4 ppm
 Ozone 0.07 ppm
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24. HOW THE IONOSPHERE IS FORMED
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25. CHARACTERISTICS OF IONOSPHERE
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26. D-LAYER
 Lowest layer of ionosphere.
 Average height = 70 km.
 Thickness = 10 km.
 Exists only day time.
 Not useful layer for HF communications.
 It reflects some VLF and LF waves.
 Absorbs MF and HF waves to some extent.
 Electron density, N = 400 electrons/cc.
 Virtual height is 60 to 80 km.
 Critical frequency = 180 KHz.
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27. E-LAYER
 Exists next to D-Layer and only in day time.
 Average height = 100 km and Thickness = 25 km.
 The ions are recombined in to molecules due to absence of
sun at night.
 Its electron density , N = 5 * 10 5 electrons/cc.
 Virtual height = 110 km.
 Critical frequency = 4 MHz .
 Maximum single – hop range = 2350 Km.
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28. Es - LAYER
 It is sporadic in nature and if at all it appears, it exists in
both day and night.
 It is a thin layer and ionization density is high.
 If it appears, it provides good reception.
 It is not a dependable layer for communication.
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29. F1 - LAYER
 It exists at a height of about 180 km in day time and
thickness is about 20 km.
 Virtual height = 180 km.
 Critical frequency = 5 MHz .
 Maximum single – hop range = 3000 km.
 HF waves are reflected to some extent and also it
absorbs HF to considerable extent.
 It passes on some HF waves towards F2- layer.
 It combines with F2 – layer during nights.
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30. F2 - LAYER
 It is most important layer for HF communication and
topmost layer of the ionosphere.
 Average height is 325 km in day time and falls to 300 km at
nights as it combines with the F1 – layer.
 Thickness = 200 km.
 It is highly ionized and exists at nights also.
 It offers better HF reflection and hence reception.
 N = 2 * 10 6 electrons/cc.
 h v = 300 km in day time and 350 km in night.
 f c = 8 MHz in day time and 6 MHz at nights.
 Maximum single – hop range = 3800 km in day time and
4100 km at night. 30

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32. REFRACTIVE INDEX OF IONOSPHERE:
It is defined as the ratio of phase velocity of a
wave in vacuum to the velocity in ionosphere.
PLASMA FREQUENCY:
•It is defined as the natural frequency of
oscillation of charged particles in plasma
region.
•Plasma is a completely ionized gas at very high
temperature consisting of the charged nuclei
and negative electrons.
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33. MECHANISM OF IONOSPHERIC PROPAGATION
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34. CRITICAL FREQUENCY:
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The highest frequency of the wave that is reflected
back from ionosphere layer is determined by the
maximum electron density of that layer called
Critical frequency of the wave and is given by :

35. CHARACTERISTIC PARAMETERS OF IONOSPHERIC
PROPAGATION
 Virtual height, hv .
 Critical frequency, fc .
 Maximum Usable Frequency, MUF.
 Skip distance.
 Lowest Usable Frequency, LUF.
 Critical angle, θc.
 Optimum working frequency, OWF or Frequency
of optimum traffic, FOT.
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36. VIRTUAL HEIGHT, hv
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•It is defined as the height that is reached by a short pulse of
energy which has the same time delay as the original wave.
•Virtual height > Actual height.
•Useful to find the angle of incidence required for the wave
to return to earth at a specified point.

37. MAXIMUM USABLE FREQUENCY, MUF
 It is the highest frequency of wave that is reflected
by the layer at an angle of incidence other than
normal.
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38. SKIP DISTANCE
 It is defined as the shortest distance from the
transmitter that is covered by a fixed frequency ( fc).
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39. LOWEST USABLE FREQUENCY, LUF:
 The lowest frequency that can be used for
communication is called LUF.
CRITICAL ANGLE, θc:
It is defined as the angle of incidence of a wave at
which the wave will not be reflected when θ > θc and it
will be reflected when θ < θc .
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40. OPTIMUM WORKING FREQUENCY, OWF
 The frequency of wave which is normally used for
Ionospheric communication is known as OWF or FOT.
 It is generally chosen to be 15 % less than the MUF.
 It is always desirable to use a high frequency as
possible since the attenuation is inversely proportional
to the square of the frequency.
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41. FADING AND DIVERSITY TECHNIQUES
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Fading is the change in the signal strength at the
receiver.
Main causes are :
Variation in Ionospheric conditions.
Multi path reception.

42. TYPES OF FADING
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RAPID
FLUCTUATIONS
LONG TERM
FLUCTUATIONS
SHORT TERM
FLUCTUATIONS
SELECTIVE FADING
INTERFERENCE FADING
ABSORPTION FADING
POLARIZATION FADING
SKIP FADING

43. DIVERSITY TECHNIQUES
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FREQUENCY DIVERSITY
SPACE DIVERSITY
POLARITY DIVERSITY
TIME DIVERSITY

44. FREQUENCY DIVERSITY
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45. SPACE DIVERSITY
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46. POLARITY DIVERSITY
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47. IONOSPHERIC ABNORMALITIES
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NORMAL ABNORMAL
DIURNAL
SEASONAL
THICKNESS
&
HEIGHT
VARIATIONS
IONOSPHERIC
STORMS
IONOSPHERIC
DISTURBANCES
SUNSPOT CYCLE
FADING
WHISTLERS
TIDES & WINDS

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50.  The EM wave that propagates from the transmitter to the
receiver is called space wave or tropospheric wave propagation.
 In space wave propagation, the field strength at the receiver is
contributed by:
Direct ray from transmitter.
Ground reflected wave.
Reflected and refracted rays from the
troposphere.
Diffracted rays around the curvature of the
earth, hills and so on.
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51. FIELD STRENGTH DUE TO SPACE WAVE
 DERIVATION
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53. CONSIDERATIONS IN SPACE WAVE PROPAGATION
 The space wave field strength is affected by the
following:
1. Curvature of the earth.
2. Earth’s imperfections and roughness.
3. Hills, tall buildings and other obstacles.
4. Height above the earth.
5. Transition between ground and space
wave.
6. polarization of the waves
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54. CURVATURE OF THE EARTH
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55. EFFECTS OF HILLS, BUILDINGS AND OTHER
OBSTACLES
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56. EFFECT OF THE HEIGHT ABOVE THE GROUND
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57. ATMOSPHERIC EFFECTS IN SPACE WAVE PROPAGATION
 Modified refractive index: It is defined as the sum of
the refractive indices at a given height above the mean
geometrical surface and the ratio of the height to the
mean geometrical radius. Mathematically,
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58. REFRACTION IN TROPOSPHERE
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59. EFFECTIVE RADIUS
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It is defined as the equivalent radius of the earth used to
correct atmospheric refraction approximately, as
refractive index of the atmosphere changes linearly with
height.

60. DUCT PROPAGATION
 It is a phenomenon of propagation making use of the
atmosphere duct region.
 The duct region exists between two levels where the variation of
modified refractive index with height is minimum.
 In duct propagation, the ray which is parallel to the earth’s
surface travels round the earth in a series of hops with successive
reflections from the earth.
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61. SALIENT FEATURES OF DUCT PROPAGATION
 It happens when dM/dh is negative.
 It happens when dielectric constant changes with the
height suddenly and rapidly.
 It is similar to waveguide propagation of microwaves.
 It is rare phenomenon and not a standard or
dependable propagation.
 It happens during monsoons, due temperature
inversion and also when low and high moisture
regions exist.
 It occurs due to super refraction.
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62. EXAMPLES OF DUCTING
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63. RADIO HORIZON
 It is defined as the locus of the distant points at which
direct rays from the antenna become tangential to
planetary surface.
 The horizon is a circle on a spherical surface.
 The distance of the horizon is affected by the
atmospheric refraction.
NOTE:
 Horizon means visible.
 It has another meaning, that is, a line at which earth
and sky appear to meet.
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64. RADIO HORIZON DISTANCE BETWEEN TRANSMITTING
AND RECEIVING ANTENNAS
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65. SALIENT FEATURES OF RADIO HORIZON
 It is the range by which a direct ray from the
transmitting antenna reaches receiving antenna.
 The earth’s curvature exhibits a horizon to space-wave
propagation. This is actually the radio horizon.
 The radio horizon extends beyond optical horizon for
standard atmosphere. This is due to bending or
refraction of the radio wave.
 Radio horizon is about 4/3 times the optical horizon.
 The radio horizon can be increased by increasing
antenna heights.
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66. FADING OF EM WAVES IN TROPOSPHERE
 Variation of dielectric constant.
 Presence of eddies.
 Uneven variations of refractive index.
 Variation of effective earth radius factor, K.
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67. LINE OF SIGHT (LOS)
 It is defined as the distance that is covered by a direct
space wave from the transmitting antenna to the
receiving antenna.
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68.  It depends on:
 Height of the receiving antenna.
 Height of the transmitting antenna.
 Effective earth’s radius factor, K.
 The line of sight distance is given by:
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69. THANK YOU
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