electromagnetic wave propagation, electromagnetic
TRANSCRIPT
M.BRAHIM
Wave Propagation
WAVE
A vibration Or Disturbance in space
EM wave propagated in space :
This diagram shows typical combination system in which signal is transmitted in the form Electromagnetic waves and received.
The electromagnetic transmission in space must be in high frequencies because in low frequency there are two problems.
Size of antenna Low radiation power.
TRANSVERSE WAVE
It is a wave which occurs in directions perpendicular to the direction of the propagation.
Transverse wave is also called travelling wave.
Specific frequency ranges
There are Three basic paths that an EM signal can take through space
Ground wave or Surface wave Space wave Sky wave
Ground wave
A frequency up to about 2MHz, the most important method of propagation is by ground wave which are vertically polarized.
They follow the curvature of earth to propagate.
Relatively high power is required.
Ground wave
Surface wave is very dependent upon the nature of the ground of which the signal travels. Such as :
Ground conductivity
Roughness
Ground wave
Space Wave
The radio waves having high frequencies are called as space wave.
The other name of space wave is Line of sight propagation
Space Wave
Those waves have the ability to propagate through atmosphere, from transmitting antenna to receiving antenna. It can travel directly or can travel after reflecting from earth’s surface to the *troposphere surface of earth.
*the lowest region of the atmosphere(15km)
Space wave
Application
It is useful for FM,T.V and RADAR application.
It is also used in VHF, UHF and microwave signals.
Sky wave
Some waves travel upwards into the space towards the sky and get reflected back to the receiver
Signal reflected ionized layer of atmosphere and back down to the earth.
These wave are called Sky wave.
Sky Wave
Signal that is radiated by the antenna into upper atmosphere where it is bent or reflected back to earth.
This bending of signal caused by a region in the upper atmosphere known as ionosphere
The Ionosphere-How is it Formed?
High energy radiation(Ultraviolet) from our sun(Solar Radiation) strikes atoms of various gasses and vapors in the earth’s upper atmosphere.
Electrons are knocked off the outer orbits of the atoms creating an ion. The process is called ionization.
Because this event takes place in the upper atmosphere, we call the layer ionosphere
D Layer
Ranges from about 30 to 55 miles
Primarily exist only during daylight hours.
E Layer
Ranges from about 55 to 90 miles
It exist only during daylight and almost gone by midnight.
Also called Kennelly-Heaviside Layer.
F Layer
Exists from about 90 to 240 miles
The most highly ionized.
In daytime, this layer split into two
parts: F1 and F2. After sunset, this
layer combines into one.
Sky wave
Application
These waves can have medium as well as high frequencies. So, due to this reason these waves can be used for long distance transmission.
This mode is used in HF band International Broadcasting
THANK YOOU