This technical document describes the Line of sight propagation from basics with diagram images

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Report on
Line of Sight propagation
Submitted
to
Dr Shukla Basu,HOD
Kalyani Government Engineering College
By
Najmul Hoque Munshi
A report submitted in partial fulfilment
of the requirements for
MCE 104
ADVANCEDMICROWAVE ENGINEERING
DEPARTMENT of ELECTRONICS AND COMMUNICATION ENGINEERING
KALYANI GOVERNMENT ENGINEERING COLLEGE

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05 OCTOBER 2018

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Abstract
In line-of-sight (LOS) radio communications, the main route is the direct path between the
transmitterandreceiverconsideringthe curvature of radiowave trajectory. This report is dedicated
to discussaboutthe principlesof space wave propagationandline of sightandalsothe LOS wireless
transmission impairments.

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TABLE OFCONTENTS
1. INTRODUCTION TO RADIO WAVE 5
2. DIRECTIONOF PROPAGATIONOF WAVE 6
3. COMMONRADIO FREQUENCYBANDS 7
4. INTRODUCTIONTO SPACEWAVES 7
5. INTRODUCTIONOF LINEOF SIGHT 8
6. LINEOF SIGHTPROPAGATION 8
7. OBSERVATION 9
8. INTRODUCTIONTO RADIO HORIZON 10
9. PRINCIPLEUSED INSPACEWAVEPROPAGATION 11
10. INTRODUCTIONTO FRESNEL ZONES 12
11. LIMITATIONOF SPACEWAVE 12
12.EFFECT OF CURVATURE OF EARTH 12
13.LOS WIRELESS TRANSMISSIONIMPAIRMENTS 13
14.SUMMARY 13

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List of figures &TABLES
FIGURES
Figure 1: Direction of propagation of Radio Wave................................6
Figure 2 : Line-of-sight propagation.......................................................8
Figure 3 : Diagram showing the relation between height of antenna and radius of earth.......9
Figure 4: Various propagation modes for EM waves.............................11
Figure 5 : Fresnel Zones.........................................................................12
TABLES
Table 1 : Common RF Band Designations...........................................7
List of symbols
C Speedof light
λ Wavelengthof the wave
F Frequencyof the wave
r Range of antenna
R Radiusof earth
h Heightof Antenna
π 22/7

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1. INTRODUCTION OF RADIOWAVE
The relationship between wavelength and frequency is give by:
c= λ f
where c is the speed of light (approximately 300,000,000 m/s in vacuum), f is the
frequency of the wave, and λ is the wavelength of the wave.
Radio waves can be reflected and refracted in a manner similar to light. They are affected by
the ground terrain, atmosphere and other objects.
Radio waves propagate outward from an antenna, at the speed of light. The exact nature of
these waves is determined by the transmission medium. In free space, they travel in straight
lines, whereas in the atmosphere, they generally travel in a curved path. In a confined or
guided medium, radio waves do not propagate in the TEM mode, but rather in a TE or TM
mode.
Radio waves interact with objects in three principle ways:
Reflection – A radio wave bounces off an object larger than its wavelength.
Diffraction – Waves bend around objects.
Scattering – A radio wave bounces off an object smaller than its wavelength.
Because of these complex interactions, radio wave propagation is often examined in three
distinct regions in order to simplify the analysis:
Surface (or ground) waves are located very near the earth’s surface.
Space waves occur in the lower atmosphere (troposphere).
Sky waves occur in the upper atmosphere (ionosphere).

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2. DIRECTIONOF PROPAGATIONOF RADIO WAVE
Electromagnetic radiation comprises both an Electric field and a Magnetic field.
If we know the directions of the E and H components, we can use the "right-hand
rule" to determine the direction of wave propagation.
The two fields are at right-angles to each other and the direction of propagation is at
right-angles to both fields.
Figure 1 : Direction of propagation of Radio Wave

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3. COMMONRADIO FREQUENCYBANDS
Frequencybandname Frequency Wavelength
ELF - ExtremelyLowFrequency 3 – 30 Hz 100000 – 10000 km
SLF - SuperLowFrequency 30 – 300 Hz 10000 – 1000 km
ULF - Ultra Low Frequency 300 – 3000 Hz 1000 – 100 km
VLF - VeryLow Frequency 3 – 30 kHz 100 – 10 km
LF - Low Frequency 30 – 300 kHz 10 – 1 km
MF - MediumFrequency 300 – 3000 kHz 1000 – 100 m
HF - HighFrequency 3 – 30 MHz 100 – 10 m
VHF - VeryHighFrequency 30 – 300 MHz 10 – 1 m
UHF - Ultra HighFrequency 300 – 3000 MHz 1000 – 100 mm
SHF - SuperHighFrequency 3 – 30 GHz 100 – 10 mm
EHF - ExtremelyHighFrequency 30 – 300 GHz 10 – 1 mm
THF - TremendouslyHighFrequency 300 – 3000 GHz 1 – 0.1 mm
Table 1 : Common RF Band Designations
4. INTRODUCTIONTO SPACEWAVES
The radio waves having high frequencies are basically called as space waves.
These waves occur within the lower 20 km of the atmosphere, and are comprised of a
direct and reflected wave.
These waves have the ability to propagate through atmosphere, from transmitter antenna
to receiver antenna. These waves can travel directly or can travel after reflecting from
earth’s surface to the troposphere surface of earth. So, it is also called as Tropospherical
Propagation. Basically the technique of space wave propagation is used in bands having
very high frequencies. E.g. V.H.F. band, U.H.F band etc. At such higher frequencies the
other wave propagation techniques like sky wave propagation, ground wave propagation
can’t work. Only space wave propagation is left which can handle frequency waves of
higher frequencies.

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5. INTRODUCTIONTO LINE-OF-SIGHT
As we all know that at low frequency (below 3 MHz) to diffraction, radio waves can
travel as ground waves, which follow the contour of the Earth.
Frequencies in the shortwave bands between approximately 1 and 30 MHz can be
reflected back to Earth by the ionosphere, called sky wave or "skip" propagation, thus
giving radio transmissions in this range a potentially global reach.
However, at frequencies above 30 MHz (VHF and higher) and in lower levels of the
atmosphere, neither of these effects are significant. Thus, any obstruction between the
transmitting antenna (transmitter) and the receiving antenna (receiver) will block the
signal, just like the light that the eye may sense. Therefore, since the ability to visually
see a transmitting antenna (disregarding the limitations of the eye's resolution) roughly
corresponds to the ability to receive a radio signal from it, the propagation characteristic
at these frequencies is called "line-of-sight". The farthest possible point of propagation is
referred to as the "radio horizon".
6. LINE-OF-SIGHT PROPAGATION
In line of sight propagation a space wave travels in a straight line from transmitting
antenna to the receiving antenna. At frequencies below 40 MHz For this type of
propagation there should be no obstacle between the transmitting antenna and the
receiving antenna.
Figure 2 : Line-of-sight propagation
In line-of-sight propagation, space waves are very powerful, the signals are very clear, the
bandwidth is very large and a huge amount of information can be transmitted.
In line-of-sight propagation, direct waves get blocked at some point by the curvature of the
earth. If the signal is to be received beyond the horizon then the receiving antenna must be

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high enough to intercept the line-of-sight waves. Range of transmission is dependent upon the
height of the antenna, relation between range and height of antenna is given by –
Figure 3 : Diagram showing the relation between height of antenna and radius of earth
From figure −
(R + h)2 = R2 + r2
∴ R2 + 2hR + h2 = R2 + r2
As we know, radius of earth is approximately 6400km while the height of the antenna is few
meters. So we can neglect h2
∴ 2hR = r2
∴ r = √2hR
Where,
r = range
h = height of antenna
R = radius of earth
7. OBSERVATION
For a greater range of electromagnetic wave, an antenna of large height is required.
Distance between two antennas for line-of-sight propagation is given by −

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r1 = √2h1R
r2 = √2h2R
∴ (r1 + r2) = √2R(h1 + h2)
Where,
r1 = range of antenna 1
r2 = range of antenna 2
h1 = height of antenna 1
h2 = height of antenna 2
R = radius of earth
Area covered by a transmitting antenna is given by −
Area = π r2
We have, r2 = 2hR
∴ Area = π 2hR
8. INTRODUCTION TO RADIO HORIZON
The radio horizon is the locus of points at which direct rays from an antenna are tangential to
the surface of the Earth. If the Earth were a perfect sphere without an atmosphere, the radio
horizon would be a circle.
The radio horizon of the transmitting and receiving antennas can be added together to
increase the effective communication range.
Radio wave propagation is affected by atmospheric conditions, ionosphere absorption, and
the presence of obstructions, for Example Mountains or trees. Simple formulas that include
the effect of the atmosphere give the range as:

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The simple formulas give a best-case approximation of the maximum propagation distance.
9. PRINCIPLE USED IN SPACE WAVE PROPAGATION
Figure 4 : Various propagation modes for EM waves
 The space wave follows two distinct paths from the transmitting antenna to the
receiving antenna – one through the air directly to the receiving antenna, the other
reflected from the ground to the receiving antenna.
 The primary path of the space wave is directly from the transmitting antenna to the
receiving antenna. So, the receiving antenna must be located within the radio horizon
of the transmitting antenna.
 Because space waves are refracted slightly, even when propagated through the
troposphere, the radio horizon is actually about one-third farther than the line-of-sight
or natural horizon. The space wave follows two distinct paths from the transmitting
antenna to the receiving antenna – one through the air directly to the receiving
antenna, the other reflected from the ground to the receiving antenna.

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 The primary path of the space wave is directly from the transmitting antenna to the
receiving antenna. So, the receiving antenna must be located within the radio horizon
of the transmitting antenna.
 Because space waves are refracted slightly, even when propagated through the
troposphere, the radio horizon is actually about one-third farther than the line-of-sight
or natural horizon.
10. INTRODUCTIONTO FRESNEL ZONES
Figure 5: Fresnel Zones
The vertical line in above figure represents the leading edge of a propagating EM plane wave
at a point in time. The rays represent paths passing through potential points of reflection or
diffraction on the wave front and converging on the receiving antenna. The points are chosen
such that the excess path length of the associated ray is equal to a multiple of one-half
wavelength (λ/2). The centre ray represents the direct LOS path. If we let the vertical distance
of each point from the LOS path represent the radius of a circle whose circumference is
tangent to that point, we have described a number of concentric, but mutually exclusive, areas
about the LOS path called Fresnel zones.
In theory, there are an infinite number of Fresnel zones about a given point, but it is the first
(inner-most) Fresnel zone that defines the critical keep-out area for an unobstructed LOS. For
obstacles that intrude into the first Fresnel zone but do not block the LOS path, it is the
constructive or destructive interference from the reflected wavefront that is of concern.A
Fresnel zone constitutes a three-dimensional area, so obstructions can intrude from above,
below, or from the sides of the LOS path.
11. LIMITATIONS OF SPACE WAVES
As a form of electromagnetic radiation, like light waves, radio waves are affected by the
phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering.
There are some limitations of space wave propagation,
i. These waves are limited to the curvature of the earth.

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ii. These waves have line of sight propagation, means their propagation is along the line
of sight distance.
12. EFFECT OF CURVATURE OF EARTH
Effect of curvature of earth when the distance between the transmitting and receiving
antennas is large, curvature of earth has considerable effect on SWP. The field strength at the
receiver becomes small as the direct ray may not be able to reach the receiving antenna. The
earth reflected rays diverge after their incidence on the earth. The curvature of earth creates
shadow zones.
13.LOS WIRELESS TRANSMISSION IMPAIRMENTS
1) Free space loss
2) Scattering –
Reception far beyond optical horizon in VHF and UHF range is
possible due to scatter propagation.
3) Atmospheric absorption –
Due to molecular interaction absorption of energy takes
place at certain wavelengths.
4) Ducting
5) Refraction
6) Reflection
7) Shadowing effect –
At VHF and above, serious disturbances in space wave
Propagation is caused by trees, buildings, hills and mountains. These obstacles cause
reflection, diffraction and absorption. Losses caused by absorption and scattering
increase with the increase of frequency until f exceeds 3 GHz. Beyond this frequency
building walls and wood become opaque to the waves. At higher frequencies the
received signal strength is considerably reduced at position on the shadow side of any
hill.
8) Fading –
A phenomenon of reduction of signals due to variation in refractive index.
14. SUMMARY
The point of this discussion has been to in still some understanding of the real world effects
that must be factored into designing a reliable telemetry link. Free space propagation losses
are the norm for calculating link budgets, but, since most telemetry links exist on the earth’s
surface and not in outer space, such calculations by themselves are insufficient. Indeed, there
are numerous other factors to be considered such as ground-wave reflections and atmospheric
losses due to scattering, absorption and ducting, but we will leave those subjects for future
discussions.