1. FACULTY DEVELOPMENT PROGRAMME on EC6602 - ANTENNA AND WAVE PROPAGATION
VALLIAMMAI ENGINEERING COLLEGE
SRM Nagar, Kattankulathur
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
FACULTY DEVELOPMENT PROGRAMME on EC ANTENNA AND WAVE PROPAGATION
UNIT – V
PROPAGATION OF RADIO WAVES
Presented By
S. RAMESH

2. PRESENTATION OUTLINE INTRODUCTION
Structure of Atmosphere , Radio Frequency (RF) Bands
Different types of Propagation Mechanism, Wave propagation Modes, Waves.
VLF (3 – 30 KHz), LF (30 – 300 KHz), MF (0.3 – 3 MHz), HF (3 – 30 MHz) & VHF(30 – 300 MHz) Propagation.
CONCLUSIONS
References
FDP-EC6602-AWP-U V-Propagation

3. OBJECTIVES To give insight of the propagation of radio waves.
To create awareness about the different types of propagation of radio waves at different frequencies.
FDP-EC6602-AWP-U V-Propagation

4. Introduction
Need-Understanding radio wave propagation can mean the difference between making and missing a contact to a particular part of the world.  
Propagation: The science and study of radio wave reflection, refraction, diffraction, absorption, polarization, and scattering.
Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere.
Like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering.
FDP-EC6602-AWP-U V-Propagation

5. Structure of Atmosphere
Ionosphere ( km)
Sky wave
Mesosphere ( km)
Stratosphere ( km)
Space wave
Ground wave
Transmitter
Receiver
Troposphere ( km)
Earth

6. Radio Frequency (RF) Bands
Classification Band
Initials
Frequency Range
Characteristics
Extremely low
ELF
< 300 Hz
Ground wave
Infra low
ILF
300 Hz - 3 kHz
Very low
VLF
3 kHz - 30 kHz
Low LF
30 kHz kHz
Medium MF
300 kHz - 3 MHz
Ground/Sky wave
High HF
3 MHz - 30 MHz
Sky wave
Very high
VHF
30 MHz MHz
Space wave
Ultra high
UHF
300 MHz - 3 GHz
Super high
SHF
3 GHz - 30 GHz
Extremely high
EHF
30 GHz GHz
Tremendously high
THF
300 GHz GHz

7. Propagation Mechanisms
Reflection
Propagation wave impinges on an object which is large as compared to wavelength.
Ex- the surface of the Earth, buildings, walls, etc.
Refraction
A transition from one medium to another results in the bending of radio waves, just as it does with light
Diffraction
Radio path between transmitter and receiver obstructed by surface with sharp irregular edges.
Waves bend around the obstacle, even when LOS (line of sight) does not exist.
Scattering
Objects smaller than the wavelength of the propagation wave.
Ex- foliage, street signs, lamp posts.

8. Propagation Mechanisms
Reflection
Refraction
Diffraction

9. Radio Propagation Effects
Building
Direct Signal
Reflected Signal hb
Diffracted Signal hm d
Transmitter
Receiver

10. Propagation Modes How Signals Travel? Ground-wave propagation
Line-of-sight propagation
Sky-wave propagation

11. Guided Waves Most VLF and LF propagation occurs via guided wave.
The ground and the ionosphere are highly conductive at this range of frequencies, and they form the “walls” of a spherical waveguide.
RF launched by a vertical antenna is trapped between the conductive shells formed by the ground and the ionosphere and is propagated over long distances.
FDP-EC6602-AWP-U V-Propagation

12. Ground Waves
In the HF region, the ground is a poor conductor and the ground wave is quickly attenuated by ground losses.
Some ground wave communication is possible on 80m, but at frequencies above 5 MHz, the ground wave is irrelevant.
FDP-EC6602-AWP-U V-Propagation

13. Ground Wave Propagation
Follows contour of the earth
Can propagate considerable distances
Frequencies up to 2 MHz
Example
AM radio

14. Ground Waves – Range Chart 80m band
FDP-EC6602-AWP-U V-Propagation

15. Direct Waves
Direct waves follow the line-of-sight (LOS) path between transmitter and receiver.
In order for direct wave communication to occur, antennas at both ends of the path have to have low angles of radiation (so they can “see” each other).
This is difficult to do on the lower bands, and as a result, direct wave communication is normally restricted to bands above 20m.
Its range is determined by the height of both antennas and generally less than 20 miles.
FDP-EC6602-AWP-U V-Propagation

16. Direct Waves – Path Geometry
The distance over which two stations can communicate using direct waves is dependent on the height of the transmitting and receiving antennas:
FDP-EC6602-AWP-U V-Propagation

17. Sky Waves What is ionosphere?
Sky waves are waves that leave the transmitting antenna in a straight line and are returned to the earth at a considerable distance by an electrically charged layer known as the ionosphere.
Communication is possible throughout much of the day to almost anywhere in the world via sky wave.
FDP-EC6602-AWP-U V-Propagation

18. Sky Wave Propagation
Signal reflected from ionized layer of atmosphere back down to earth
Signal can travel a number of hops, back and forth between ionosphere and earth’s surface
Reflection effect caused by refraction
Examples
Amateur radio
CB radio

19. Introduction - VLF and LF propagation
The dominant factor in VLF(3 – 30 KHz) and LF(30– 300 KHz) propagation is the extremely large wavelength of the waves.
l ~ 1 – 10 km (VLF)
l ~ 0.1 – 1 km (LF)
Wavelength is so large, horizontal antennas are not practical (imagine trying to construct a dipole 5km long that is 5km above ground) and only vertical polarization is used.
Although amateurs in the US do not have an LF allocation, some European countries do, at 137 KHz.
FDP-EC6602-AWP-U V-Propagation

20. Introduction - HF propagation
The HF (3–30 MHz) region is the one of two regions of RF frequencies that consistently supports long distance propagation.
The HF region includes:
International broadcasting at on the 120, 90, 60, 49,41,31,25,19,16, and 13 meter bands.
Amateur Radio Service operations on the 80, 40, 30, 20, 17, 15, 12, and 10 meter bands.
Citizens’ Band operation on 11 meters (27 MHz)
Point-to-point military and diplomatic communications
FDP-EC6602-AWP-U V-Propagation

21. Overview of HF Propagation
Characteristics of HF radio propagation
Propagation is possible over thousands of miles.
It is highly variable. It has daily and seasonal variation, as well as a much longer 11 year cycle.
HF radio waves may travel by any of the following modes:
Ground Wave
Direct Wave (line-of-sight)
Sky Wave
     
FDP-EC6602-AWP-U V-Propagation

22. Created by ionization of the upper atmosphere by the sun.
Ionosphere
Created by ionization of the upper atmosphere by the sun.
Electrically active as a result of the ionization.
Bends and attenuates HF radio waves
Above 200 MHz, the ionosphere becomes completely transparent
Creates most propagation phenomena observed at HF, MF, LF and VLF frequencies.
FDP-EC6602-AWP-U V-Propagation

23. Ionospheric Layers Consists of 4 highly ionized regions
The D layer at a height of 38 – 55 mi
The E layer at a height of 62 – 75 mi
The F1 layer at a height of 125 –150 mi (winter) and 160 – 180 mi (summer)
The F2 layer at a height of 150 – 180 mi (winter) and 240 – 260 mi (summer)
The density of ionization is greatest in the F layers and least in the D layer.
FDP-EC6602-AWP-U V-Propagation

24. Ionosphere Layer Formation
Though created by solar radiation, it does not completely disappear shortly after sunset.
The D and E layers disappear very quickly after sunset.
The F1 and F2 layers do not disappear, but merge into a single F layer residing at a distance of 150 – 250 mi above the earth.
Ions recombine much faster at lower altitudes.
Recombination at altitudes of 200 mi is slow that the F layer lasts until dawn.
FDP-EC6602-AWP-U V-Propagation

25. Ionosphere Profiles
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26. D-Layer Extends from 38 – 55 miles’ altitude.
Is created at sunrise, reaches maximum density at noon, and disappears by sunset.
The D layer plays only a negative role in HF communications.
It acts as an attenuator, absorbing the radio signals, rather than returning them to earth.
The absorption is inversely proportional to the square of the frequency, severely restricting communications on the lower HF bands during daylight.
FDP-EC6602-AWP-U V-Propagation

27. E - layer Extends from 38 – 55 miles’ altitude.
Is created at sunrise, reaches maximum density at noon, and disappears by sunset.
It can return lower HF frequencies to the Earth, resulting in daytime short skip on the lower HF bands.
It has very little effect on higher frequency HF radio waves, other than to change slightly their direction of travel.
FDP-EC6602-AWP-U V-Propagation

28. RF Refraction through the E-Layer

29. F Layers
The F1 layer extends from 125 –150 mi (winter) and 160 – 180 mi (summer)
The F2 layer extends from 150 – 180 mi (winter) and mi (summer)
The F layers are primarily responsible for long-haul HF communications.
Because there is only F layer ionization throughout the hours of darkness, it is carries almost all nighttime communications over intercontinental distances.
FDP-EC6602-AWP-U V-Propagation

30. Daily Propagation Effects
Shortly after sunrise, the D and E layers are formed and the F layer splits into two parts.
The D layer acts as a selective absorber, attenuating low frequency signals, making frequencies below 5 or 6 MHz useless during the day for DX work.
The E and F1 layers increase steadily in intensity from sunrise to noon and then decreases thereafter.
Short skip propagation via the E or F1 layers when the local time at the ionospheric refraction point is approximately noon.
The MUF’s for the E and F1 layers are about 5 and 10 MHz respectively.
The F2 layer is sufficiently ionized to HF radio waves and return them to earth.
For MUF’s is above MHz, long distance communications are possible.
MUF’s falls below 5 MHz, the frequencies that can be returned by the F layer are completely attenuated by the D layer.
FDP-EC6602-AWP-U V-Propagation

31. Seasonal Propagation Effects
During the winter months, the atmosphere is colder and denser.
The ionosphere moves closer to the earth increasing the electron density.
During the Northern Hemisphere winter, the earth makes its closest approach to the sun, which increases the intensity of the UV radiation striking the ionosphere.
Electron density during the northern hemisphere winter can be 5 times greater than summer’s.
Winter MUF’s are approximately double summer’s.
FDP-EC6602-AWP-U V-Propagation

32. Propagation Disturbances
A solar flare is a plume of very hot gas ejected from the sun’s surface.
rises through chromosphere into the corona, disturbing both regions.
X-ray emission from the corona increases, which reaches Earth in less than 9 minutes.
If they are intense enough, the ionosphere will become so dense that all HF signals are absorbed by it and worldwide HF communications are blacked out.
Generally ionospheric disturbances affect the lowest HF bands most. Occasionally communications on 10m may be possible.
FDP-EC6602-AWP-U V-Propagation

33. VHF(30 – 300 MHz) Propagation Modes
Every type of propagation is possible in the VHF range:
Line of Sight (LOS)
Tropospheric Propagation (tropo)
Sporadic E
Meteor Scatter
Auroral Scattering
Trans-equatorial F1
Ionospheric F2
LOS and tropo occur throughout the VHF range, while the other modes are most frequently observed below 150 MHz.
FDP-EC6602-AWP-U V-Propagation

34. LOS and Tropospheric Propagation
Line of Sight
LOS coverage is determined primarily by the height of the transmitting and receiving antennas
For typical amateur 6 m stations LOS coverage is about 20 miles
LOS propagation is unaffected by solar conditions.
Tropospheric Propagation
Tropospheric scatter-Variations in humidity of troposphere cause RF to be scattered over the horizon.
Temperature inversions refract RF in VHF range back towards earth. Temperature inversions occur daily in the middle latitudes at sunrise and sunset. Communications are possible over a ranges up to 600 miles.
Over the oceans, stable temperature inversions can create a duct, through which VHF can travel without significant loss up to miles.
FDP-EC6602-AWP-U V-Propagation

35. Tropospheric Ducting Tropospheric Scatter
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36. CONCLUSIONS
Created awareness about the different types of propagation of radio waves at different frequencies
Brief overview of RF propagation. There have been many books written on this subject and a there are many computer resources available, particularly for propagation forecasting.
The Radio Society of Great Britain has an interesting website devoted to propagation,
FDP-EC6602-AWP-U V-Propagation

37. R.E.Collin,”Antennas and Radiowave Propagation”, Mc Graw Hill 1985.
REFERENCES
R.E.Collin,”Antennas and Radiowave Propagation”, Mc Graw Hill 1985.
H.Sizun “Radio Wave Propagation for Telecommunication Applications”, First Indian Reprint, Springer Publications, 2007.
FDP-EC6602-AWP-U V-Propagation

38. THANK YOU
FDP-EC6602-AWP-U V-Propagation