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

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