2 sd semester 1439 - 2018

1. Lecture 4:Wave Propagation Concept 2sdsemester 1439 - 2018 By: Elham Sunbu

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

3. Wave Propagation 2 1 • What does propagation means? • Toreproduce • To cause tospread. • What is a wave? • A vibration or disturbance. • Sound& lightare 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 candistinguishbetween 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 avacuum 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 • Crest= High point of a wave. • Trough=Lowpoint of a wave. • Amplitude(A)= Distance from the midpoint to the crest. • Wavelength(λ)= The length of one complete wave. PARTS OF AWAVE

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

9. The type of medium changes the way a wavemoves. • Mediums with close molecules travel quickly. • This is why waves travel better in liquidsandsolidsthan in gases. TYPE OF MEDIUM

10. Therearetwoprincipalwaysin 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). • Skywaves- areradiowavesthatare reflectedback to Earth from the ionosphere. RADIO WAVE TRANSMISSION

11. 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 TYPES OF PROPAGATION

12. 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 toprovide relatively local radiocommunications coverage. GROUND WAVE PROPAGATION

14. 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. GROUND (SURFACE) WAVE

15. Surface wave is very dependant upon the nature ofthe ground ofwhich 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 Effects of the Ground

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 throughatmosphere, from transmitter antenna to receiver antenna. • These waves can travel directly or can travel afterreflecting 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 thespace wave propagation.

18. 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. Limitations of space wave propagation

19. 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 Applications

20. : • 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? • Solve: • D=53.2 mi Example

21. 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 SKYWAVE PROPAGATION

22. Advantages and disadvantages

23. RANGE OF WAVE PROPAGATION

24. Thank You