1. Lecture 4: Wave Propagation Concept
2sd semester
By: Elham Sunbu

2. Outline WAVE PROPAGATION PARTS OF A WAVE ELECTROMAGNETIC SPECTRUM
TYPES OF PROPAGATION

3. Wave Propagation How radio waves travel between two points?2 1
What does propagation means?
To reproduce
To cause to spread.
What is a wave?
A vibration or disturbance.
Sound & light are forms of energy that travel in waves.
How radio waves travel between two points?
They generally do this in four ways:
Directly from one point to another
Follow the curvature of the earth
Become trapped in the atmosphere and traveling longer distances
Refracting off the ionosphere back to earth.

4. Wave Propagation
Wave propagation is any of the ways in which waves travel.
With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transvers waves
For electromagnetic waves, propagation may occur in a vacuum as well as in a material medium. Other wave types cannot propagate through a vacuum and need a transmission medium to exist.

5. The process of communication involves the transmission of information from one location to another. An electromagnetic wave is created by a local disturbance in the electric and magnetic fields. From its origin, the wave will propagate outwards in all directions. If the medium in which it is propagating (air for example) is the same everywhere, the wave will spread out uniformly in all directions.

6. PARTS OF A WAVE

7. PARTS OF A WAVE PARTS OF A WAVE Crest= High point of a wave.
Trough=Low point of a wave.
Amplitude (A)= Distance from the midpoint to the crest.
Wavelength (λ)= The length of one complete wave.
PARTS OF A WAVE

8. ELECTROMAGNETIC SPECTRUM
Energy that is given off by electrons that moves in waves.

9. TYPE OF MEDIUM The type of medium changes the way a wave moves.
Mediums with close molecules travel quickly.
This is why waves travel better in liquids and solids than in gases.

10. RADIO WAVE TRANSMISSION
There are two principal ways in Which electromagnetic (radio) energy travels from a transmitting antenna to a receiving antenna. One way is by GROUND WAVES and the other is by SKY WAVES.
Ground waves - are radio waves that travel near the surface of the Earth (surface and space waves).
Sky waves - are radio waves that are reflected back to Earth from the ionosphere.

11. TYPES OF PROPAGATION
Propagation of Radio waves takes place by different modes, the mechanism being different in each case. Based on that, it can be classified as:
Ground (Surface) waves
Space (Tropospheric) waves
Sky (Ionospheric) waves

12. GROUND WAVE PROPAGATION
Ground Wave propagation is a method of radio frequency propagation that uses the area between the surface of the earth and the ionosphere for transmission.
The ground wave can propagate a considerable distance over the earth's surface particularly in the low frequency and medium frequency portion of the radio spectrum.
Ground wave radio propagation is used to provide relatively local radio communications coverage.

14. GROUND (SURFACE) WAVE
The ground wave is actually composed of two separate component waves. These are known as the SURFACE WAVE and the SPACE WAVE.
A surface wave travels along the surface of the Earth. A space wave travels over the surface.

15. Effects of the Ground
Surface wave is very dependant upon the nature of the ground of which the signal travels. Such as the ff:
Ground conductivity
Terrain roughness
Dielectric constant
at lower frequency ground penetration is greater
at higher frequency ground penetration is smaller

16. SURFACE WAVE PROPAGATION

17. SPACE WAVE PROPAGATION
The radio waves having high frequencies are basically called as space waves.
The other name of space wave propagation is line of sight propagation (LOS)
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. In the diagram of medium wave propagation, c shows the space wave propagation.

18. Limitations of space wave propagation
These waves are limited to the curvature of the earth
These waves have line of sight propagation, means their propagation is along the line of sight distance.
Note:
To extend transmission distances at VHF, UHF, and microwaves, relay stations known as repeater stations are used.

19. Applications D= √2ht +√2hr
It is useful for FM,TV and radar applications. It is also used in VHF,UHF and microwave signals.
The distance between transmitting and receiving antennas has a formula:
D= √2ht +√2hr

20. Example :
Q1) If the transmitting antenna is 150 ft high and the receiving antenna is 40 ft high, the greatest transmission distance is:
Solve:
D=26.2 mi.
Q2) A microwave transmitting antenna is 550 ft high. The receiving antenna is 200 ft high. The maximum transmission distance is?
D=53.2 mi

21. SKY WAVE PROPAGATION
Sky-wave propagation refers to radio wave propagation via the ionosphere.
Each reflection from the ionosphere is a hop.
Reception of sky-wave propagation is called skip.
The higher the region in the ionosphere where the hop occurs, the greater the distance the wave can travel.
F2 skip can travel up to 2500 miles. E skip can travel up to 1200 miles .
Sky-wave propagation can include multiple hops between the Earth and the ionosphere

22. Advantages and disadvantages
Most long-distance shortwave radio communication—between 3 and 30 MHz—is a result of sky wave propagation.
The signal received are subjected to fading, in which signal strength varies with time.
Since the early 1920s amateur radio operators , limited to lower transmitter power than broadcast stations, have taken advantage of sky wave for long distance communication.
The receiving point, a large number of waves follow a different number of paths

23. RANGE OF WAVE PROPAGATION

24. Thank You